Internet-Draft IP Addressing Considerations June 2023
Iannone Expires 28 December 2023 [Page]
Network Working Group
Intended Status:
L. Iannone, Ed.

IP Addressing Considerations


The Internet Protocol (IP) has been the major technological success in information technology of the last half century. As the Internet becomes pervasive, IP has been replacing communication technology for many domain-specific solutions, but it also has been extended to better fit the specificities of the different use cases. For Internet addressing in particular, as it is defined in RFC 791 for IPv4 and RFC 8200 for IPv6, respectively, there exist many extensions. Those extensions have been developed to evolve the addressing capabilities beyond the basic properties of Internet addressing. This discusses the properties the IP addressing model, showcasing the continuing need to extend it and the methods used for doing so.

The most important aspect of the analysis and discussion in this document is that it represents a snapshot of the discussion that took place in the IETF (on various mailing lists and several meetings) in the early 2020s. While the community did not converge on specific actions to be taken, the content of this document may nonetheless be of use at some point in the future should the community decide so.

Status of This Memo

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This Internet-Draft will expire on 28 December 2023.

Table of Contents

1. Rationale

The Internet Protocol (IP), positioned as the unified protocol at the (Internet) network layer, is seen by many as key to the innovation stemming from Internet-based applications and services. Even more so, with the success of the TCP/IP protocol stack, IP has been gradually replacing existing domain-specific protocols, evolving into the core protocol of the ever-growing communication eco-system.

At its inception, roughly 40 years ago [RFC0791], the Internet addressing system, represented in the form of the IP address and its locator-base (topological) semantics, has brought about the notion of a 'common namespace for all communications'. Compared to proprietary technology-specific solutions, such 'common namespace for all communications' ensures end-to-end communication from any device connected to the Internet to another.

However, use cases, associated services, node behaviors, and requirements on packet delivery have since been significantly extended, with suitable Internet technology being developed to accommodate them in the framework of addressing that stood at the aforementioned beginning of the Internet's development. This continuing evolution includes addressing and, therefore, the address structure, as well as the semantic that is being used for packet forwarding (e.g., service identification, content location, device type). In this, the topological location centrality of IP is fundamental when reconciling the often-differing semantics for 'addressing' that can be found new use cases. Due to this centrality, use cases often have to adopt specific solutions, e.g., translating/mapping/converting concepts, semantics, and ultimately, solution-specific addressing, and integrate them into the common IP addressing model.

The IETF community has, at various times, discussed the IP addressing model and its possible evolution, while keeping its structure unchanged, so to accommodate future use cases and existing deployments. This document does (or at least tries to) capture the discussion that the IETF community held about IP addressing model in the early 2020s. The discussion originated from two memos proposing an analysis of the extensions developed to better adapt the IP addressing model to specific use cases [I-D.iannone-internet-addressing-considerations] and a (shorter) companion memo trying to formalize a related problem statement [I-D.iannone-scenarios-problems-addressing]. Further, an informal side meeting was organized during IETF 112 [SIDE112] with a panel of experts, which had a lively discussion. That discussion continued, with a very large volume of messages, on the INTArea mailing list and other mailing lists, like architectural discuss, honing into the related question on what desired features a network should provide in the first place (see Appendix A for a summary of the feature listed in that discussion). The IAB also touched briefly the topic in one of their retreats. The momentum and the amplitude of the discussion did raise the question whether or not to go for a formal Working Group, although the community failed to converge on a specific direction that could eventually lead to an evolution of the IP addressing model and at the same time the steam diminished.

The latest revision of the aforementioned individual submissions captured the discussion of the wider community, summarizing mail exchange and including contributions from a large set of co-authors. This separate memo includes a large portion of those documents, in addition to follow-up discussions since, with the purpose to document the inputs, thoughts, and opinions of a part of the IETF community.

2. Introduction

As the Internet Protocol adoption has grown towards the global communication system we know today, its characteristics have evolved subtly, with [RFC6250] documenting various aspects of the IP service model and its frequent misconceptions, including Internet addressing. The very origin of the discussion resulting in this document was the observation that in various use-cases, addressing has evolved and is somehow adapted or extended.

These desired features have implications that go beyond addressing and need to be tackled from a larger architectural point of view. Nevertheless, the discussion that took place only focused on the addressing viewpoint, identifying shortcomings perceived from this perspective, in particular with respect to IP addressing properties. The key properties of Internet addressing, outlined in Section 3, are (i) the fixed length of the IP addresses, (ii) the ambiguity of IP addresses semantic, while still (iii) providing limited IP address semantic support. Those properties are derived directly as a consequence of the respective standards that provide the basis for Internet addressing, most notably [RFC0791] for IPv4 and [RFC8200] for IPv6, respectively. The limitations of the IP addressing properties are discussed in Section 4, including the various use cases and scenarios where such limitations actually show up.

What is interesting to note is that different use-cases may actually been handled with the same type of extension. This shows that, based on an architectural approach, evolving the properties discussed in Section 3 is possible and even desirable since it has the advantage to be designed in a coherent fashion, avoiding point-solutions which may create contention when deployed. To this end, Section 5 discusses Internet addressing properties extensions, associating the different use-cases that take advantage of the property's extensions.

While the various extensions proposed through the years certainly did a fine job in solving the problem at hand, this "patching" approach raises also concerns. Section 6 outlines considerations and concerns that arise with such extension-driven approach, arguing that any requirements for solutions that would revise the basic Internet addressing would require to address those concerns.

3. Current Properties of Internet Protocol Addressing

In this section, the three most acknowledged properties related to Internet addressing are detailed. Those are (i) fixed IP address length, (ii) ambiguous IP address semantic, and (iii) limited IP address semantic support.

3.1. Property 1: Fixed Address Length

The fixed IP address length is specified as a key property of the design of Internet addressing, with 32 bits for IPv4 ([RFC0791]), and 128 bits for IPv6 ([RFC8200]), respectively. Given the capability of the hardware at the time of IPv4 design, a fixed length address was considered as a more appropriate choice for efficient packet forwarding. Although the address length was once considered to be variable during the design of Internet Protocol Next Generation ("IPng", cf., [RFC1752]) in the 1990s, it finally inherited the design of IPv4 and adopted a fixed length address towards the current IPv6. As a consequence, the 128-bit fixed address length of IPv6 is regarded as a balance between fast forwarding (i.e., fixed length) and practically boundless cyberspace (i.e., enabled by using 128-bit addresses).

3.2. Property 2: Ambiguous Address Semantic

Initially, the meaning of an IP address has been to identify an interface on a network device, although, when [RFC0791] was written, there were no explicit definitions of the IP address semantic.

With the global expansion of the Internet protocol, the semantic of the IP address is commonly believed to contain at least two notions, i.e., the explicit 'locator', and the implicit 'identifier'. Because of the increasing use of IP addresses to both identify a node and to indicate the physical (or virtual) location of the node, the intertwined address semantics of identifier and locator was then gradually observed and first documented in [RFC2101] as 'locator/identifier overload' property. With this, the IP address is used as an identification for host and server, very often directly used, e.g., for remote access or maintenance.

3.3. Property 3: Limited Address Semantic Support

Although IPv4 [RFC0791] did not add any semantic to IP addresses beyond interface identification (and location), time has proven that additional semantics are desirable (c.f., the history of 127/8 [HISTORY127] or the introduction of private addresses [RFC1918]). Later on, IPv6 [RFC4291] introduced some form of additional semantics based on specific prefix values, for instance link-local addresses or a more structured multicast addressing. Nevertheless, systematic support for rich address semantics remains limited and basically prefix-based.

4. Perceived IP Addressing Shortcomings

What follows is the list identified during the various exchange, which is however not to be considered exhaustive.

  1. Limiting Alternative Address Semantics: Several communication scenarios pursue the use of alternative semantics (e.g., for privacy, for service identification, or for content identification) preserving what constitute an 'address' of a packet traversing the Internet, which may fall foul of the defined network interface semantic of IP addresses.
  2. Hampering Security: Aligning with the semantic and length limitations of IP addressing may hamper the security objectives of any new semantic, possibly leading to detrimental effects and possible other workarounds (at the risk of introducing fragility rather than security).
  3. Hampering Privacy: The simple use of IP addresses as global stable interface identifiers raises clear privacy concerns. It goes beyond profiling the traffic of end users, since it can even be easily used to obtain the real identity of individuals.
  4. Complicating Traffic Engineering: Utilizing a plethora of non-address inputs (e.g., port numbers, segments ID, payload) into the traffic steering decision in real networks may complicate traffic engineering in that it makes the development of suitable policies more complex, while also leading to possible contention between methods being used.
  5. Hampering Efficiency: Extending IP addressing through point-wise solutions also hampers efficiency, e.g., through needed re-encapsulation (therefore increasing the header processing overhead as well as header-to-payload ratio), through introducing path stretch, or through requiring compression techniques to reduce the header proportion of large addresses when operating in constrained environments.
  6. Fragility: The introduction of point solutions, each of which comes with possibly own usages of address or packet fields, together with extension-specific operations, increases the overall fragility of the resulting system, caused, for instance, through contention between feature extensions that were neither foreseen in the design nor tested during the implementation phase.
  7. Extensibility: Accommodating new requirements through ever new extensions as an extensibility approach to addressing compounds aspects discussed before, i.e., fragility, efficiency etc. It complicates engineering due to the clearly missing boundaries against which contentions with other extensions could be managed. It complicates standardization since extension-based extensibility requires independent, and often lengthy, standardization processes. And ultimately, deployments are complicated due to backward compatibility testing required for any new extension being integrated into the deployed system.

The above shortcomings are not apparent in every possible use case, rather they appear, in a more or less severe form, in specific use cases. Hereafter, a set of such kind of use cases, for which extensions to the IP addressing model have been already proposed on a case-by-case basis, is listed. An extensive discussion about these use cases and related extensions can be found in Appendix B. Here, for each use case, a very short description is provided, while Table 1 shows how the previously identified issues do arise somehow in these use cases.

Table 1: Issues Involved in Challenging Scenarios.
  Issue 1 Issue 2 Issue 3 Issue 4 Issue 5 Issue 6
Constrained Environments       x x x
Dynamically Changing Topologies x   x x x x
Moving Endpoints x   x x x x
Across Services x   x x x x
Traffic Steering x   x x x x
Built-in Security x x   x x x
Alternative Forwarding Architectures x     x   x

5. Existing IP Addressing Extensions

As already stated, during the years various technologies have been developed that circumvent some IP addressing shortcomings, basically extending the properties defined in Section 3. Hereafter, an overview of such existing extensions is provided, grouped by property. For each group, a general description and the methodology used by the various extensions is provided. Details about the cited technologies relates to properties extension can be found in Appendix C.

5.1. Length Extensions

Extensions in this subsection aim at extending the property described in Section 3.1, i.e., the fixed IP address length.

When IPv6 was designed, the main objective was to create an address space that would not lead to the same situation as IPv4, namely to address exhaustion. To this end, while keeping the same addressing model like IPv4, IPv6 adopted a 128-bit address length with the aim of providing a sufficient and future-proof address space. The choice was also founded on the assumption that advances in hardware and Moore's law would still allow to make routing and forwarding faster, and the IPv6 routing table manageable.

We observe, however, that the rise of new use cases but also the number of new devices, e.g., industrial/home or small footprint devices, was possibly unforeseen. Sensor networks and more generally the Internet of Things (IoT) emerged after the core body of work on IPv6, thus different from IPv6 assumptions, 128-bit addresses were costly in certain scenarios. On the other hand, given the huge investments that IPv6 deployment involved, certain solutions are expected to increase the addressing space of IPv4 in a compatible way, and thus extend the lifespan of the sunk investment on IPv4.

At the same time, it may also be possible to use variable and longer address lengths to address current networking demands. For example, in content delivery networks, longer addresses such as URLs are required to fetch content, an approach that Information-Centric Networking (ICN) applied for any data packet sent in the network, using information-based addressing at the network layer. Furthermore, as an approach to address the routing challenges faced in the Internet, structured addresses may be used in order to avoid the need for routing protocols. Using variable length addresses allow as well to have shorter addresses. So, for requirements for smaller network layer headers, shorter addresses could be used, maybe alleviating the need to compress other fields of the header. Furthermore, transport layer port numbers can be considered short addresses, where the high order bits of the extended address are the public IP of a NAT. Hence, in IoT deployments, the addresses of the devices can be really small and based on the port number, but they all share the global address of the gateway to make each one having a globally unique address.

5.1.1. Shorter Address Length Description

In the context of IoT [RFC7228], where bandwidth and energy are very scarce resources, the static length of 128-bit for an IP address is more a hindrance than a benefit since 128-bit for an IP address may occupy a lot of space, even to the point of being the dominant part of a packet. In order to use bandwidth more efficiently and use less energy in end-to-end communication, solutions have been proposed that allow for very small network layer headers instead. Methodology
Header Compression/Translation:

One of the main approaches to reduce header size in the IoT context is by compressing it. Such technique is based on a stateful approach, utilizing what is usually called a 'context' on the IoT sensor and the gateway for communications between an IoT device and a server placed somewhere in the Internet - from the edge to the cloud.

  • The role of the 'context' is to provide a way to 'compress' the original IP header into a smaller one, using shorter address information and/or dropping some field(s); the context here serves as a kind of dictionary.

Separate device from locator identifier:

Approaches that can offer customized address length that is adequate for use in such constrained domains are preferred. Using different namespaces for the 'device identifier' and the 'routing' or 'locator identifier' is one such approach.

5.1.2. Longer Address Length Description

Historically, obtaining adequate address space is considered as the primary and raw motivation to invent IPv6. Longer address (more than 32-bit of IPv4 address), which can accommodate almost inexhaustible devices, used to be considered as the surest direction in 1990s. Nevertheless, to protect the sunk cost of IPv4 deployment, certain efforts focus on IPv4 address space depletion question but engineer IPv4 address length in a more practical way. Such effort, i.e., NAT (Network Address Translation), unexpectedly and significantly slows IPv6 deployment because of its high cost-effectiveness in practice.

Another crucial need for longer address lengths comes from "semantic extensions" to IP addresses, where the extensions themselves do not fit within the length limitation of the IP address. This sub-section focuses on address length extensions that aim at reducing the IPv4 addresses depletion, while Section 5.3, i.e., address sematic extensions, may still refer to extensions when longer address length are suitable to accommodate different address semantic. Methodology
Split address zone by network realm:

This methodology first split the network realm into two types: one public realm (i.e., the Internet), and innumerable private realms (i.e., local networks, which may be embedded and/or having different scope). Then, it splits the IP address space into two type of zones: global address zone (i.e., public address) and local address zone (e.g., private address, reserved address). Based on this, it is assumed that in public realm, all devices attached to it should be assigned an address that belongs to the global address zone. While for devices attached to private realms, only addresses belonging to the local address zone will be assigned. Local realms may have different scope or even be embedded one in another, like for instance, light switches local network being part of the building local network, which in turn connects to the Internet. In the local realms, addresses may have a pure identification purpose. For instance, in the last example, addresses of the light switches identify the switches themselves, while the building local network is used to locate them.

  • Given that the local address zone is not globally unique, certain mechanisms are designed to express the relationship between the global address zone (in public realm) and the local address zone (in any private realm). In this case, global addresses are used for forwarding when a packet is in the public realm, and local addresses are used for forwarding when a packet is in a private realm.

5.1.3. Examples

Table 2 summarizes methodologies and lists examples of IP address length extensions.

Table 2: Summary Length Extensions
  Methodology Examples
Shorter Address Length Header compression/translation 6LoWPAN, ROHC, SCHC
  Separate device from locator identifier EIBP, LISP, ILNP, HIP
Longer Address Length Split address zone by network realm NAT, EzIP

5.2. Identity Extensions

Extensions in this subsection attempt extending the property described in Section 3.2, i.e., 'locator/identifier overload' of the ambiguous address semantic.

From the perspective of Internet users, on the one hand, the implicit identifier semantic results in a privacy concern due to network behavior tracking and association. Despite that IP address assignments may be dynamic, they are nowadays considered as 'personal data' and as such undergoes privacy protection regulations like General Data Protection Regulation ("GDPR" [VOIGT17]). Hence, additional mechanisms are necessary in order to protect end user privacy.

For network regulation of sensitive information, on the other hand, dynamically allocated IP addresses are not sufficient to guarantee device or user identification. As such, different address allocation systems, with stronger identification properties are necessary where security and authentication are at highest priority. Hence, in order to protect information security within a network, additional mechanisms are necessary to identify the users or the devices attached to the network.

5.2.1. Anonymous Address Identity Description

As discussed in Section 3.2, IP addresses reveal both 'network locations' as well as implicit 'identifier' information to both traversed network elements and destination nodes alike. This enables recording, correlation, and profiling of user behaviors and historical network traces, possibly down to individual real user identity. The IETF, e.g., in [RFC7258], has taken a clear stand on preventing any such pervasive monitoring means by classifying them as an attack on end users' right to be left alone (i.e., privacy). Regulations such as the EU's General Data Protection Regulation (GDPR) classifies, for instance, the 'online identifier' as personal data which must be carefully protected; this includes end users' IP addresses [VOIGT17].

Even before pervasive monitoring [RFC7258], IP addresses have been seen as something that some organizational owners of networked system may not want to reveal at the individual level towards any non-member of the same organization. Beyond that, if forwarding is based on semantic extensions, like other fields of the header, extension headers, or any other possible extension, if not adequately protected it may introduce privacy leakage and/or new attack vectors. Methodology
Traffic Proxy:

Detouring the traffic to a trusted proxy is a heuristic solution. Since nodes between trusted proxy and destination (including the destination per se) can only observe the source address of the proxy, the 'identification' of the origin source can thereby be hidden. To obfuscate the nodes between origin and the proxy, the traffic on such route would be encrypted via a key negotiated either in-band or off-band. Considering that all applications' traffic in such route can be seen as a unique flow directed to the same 'unknown' node, i.e., the trusted proxy, eavesdroppers in such route have to make more efforts to correlate user behavior through statistical analysis even if they are capable of identifying the users via their source addresses. The protection lays in the inability to isolate single application specific flows. According to the methodology, such approach is IP version independent and works for both IPv4 and IPv6.

Source Address Rollover:

Privacy concerns related to address 'identifier' semantic can be mitigated through regular change (beyond the typical 24 hours lease of DHCP). Due to the semantics of 'identifier' that an IP address carries, such approach promotes to change the source IP address at a certain frequency. Under such methodology, the refresh cycling window may reach to a balance between privacy protection and address update cost. Due to the limited space that IPv4 contains, such approach usually works for IPv6 only.

Private Address Spaces:

Their introduction in [RFC1918] foresaw private addresses (assigned to specific address spaces by the IANA) as a means to communicate purely locally, e.g., within an enterprise, by separating private from public IP addresses. Considering that private addresses are never directly reachable from the Internet, hosts adopting private addresses are invisible and thus 'anonymous' for the Internet. Besides, hosts for purely local communication used the latter while hosts requiring public Internet service access would still use public IP addresses.

Address Translation:

The aforementioned original intention for using private IP addresses, namely for purely local communication, resulted in a lack of flexibility in changing from local to public Internet access on the basis of what application would require which type of service.

  • If eventually every end-system in an organization would require some form of public Internet access in addition to local one, an adequate number of public Internet addresses would be required for providing to all end systems. Instead, address translation enables to utilize many private IP addresses within an organization, while only relying on one (or few) public IP addresses for the overall organization.

  • In principle, address translation can be applied recursively. This can be seen in modern broadband access where Internet providers may rely on carrier-grade address translation for all their broadband customers, who in turn employ address translation of their internal home or office addresses to those (private again) IP addresses assigned to them by their network provider.

  • Two benefits arise from the use of (private to public IP) address translation, namely (i) the hiding of local end systems at the level of the (address) assigned organization, and (ii) the reduction of public IP addresses necessary for communication across the Internet. While the latter has been seen for long as a driver for address translation, in this section, we focus on the first one, also since we see such privacy benefit as well as objective as still being valid in addressing systems like IPv6 where address scarcity is all but gone [GNATCATCHER].

Separate device from locator identifier:

Solutions that make a clear separation between the routing locator and the identifier, can allow for a device ID of any size, which in turn can be encrypted by a network element deployed at the border of routing domain (e.g., access/edge router). Both source and end-domain addresses can be encrypted and transported, as in the routing domain, only the routing locator is used.

5.2.2. Authenticated Address Identity Description

In some scenarios (e.g., corporate networks) it is desirable to being able authenticate IP addresses in order to prevent malicious attackers spoofing IP addresses. This is usually achieved by using a mechanism that allows to prove ownership of the IP address. Another growing use case where identity verification is necessary for security and safety reasons is in the aeronautical context, for both manned and unmanned aerial vehicles ([RFC9153], [I-D.haindl-lisp-gb-atn]). Methodology
Self-certified addresses:

This method is usually based on the use of nodes' public/private keys. A node creates its own interface ID (IID) by using a cryptographic hash of its public key (with some additional parameters). Messages are then signed using the nodes' private key. The destination of the message will verify the signature through the information in the IP address. Self-certification has the advantage that no third party or additional security infrastructure is needed. Any node can generate its own address locally and then only the address and the public key are needed to verify the binding between the public key and the address.

Collision-resistant addresses:

When self-certification cannot be used, an alternative approach is to generate addresses in a way that is statistically unique (collision-resistant). Authentication of the address then occurs in an out-of-band protocol, where the unique identifier is resolved to authenticating information.

Third party granted addresses:

DHCP (Dynamic Host Configuration Protocol) is widely used to provide IP addresses, however, in its basic form, it does not perform any check and even an unauthorized user without the right to use the network can obtain an IP address. To solve this problem, a trusted third party has to grant access to the network before generating an address (via DHCP or other) that identifies the user. User authentication done securely either based on physical parameters like MAC addresses or based on an explicit login/password mechanism.

5.2.3. Examples

Table 3, summarize the methodologies and lists examples of identity extensions.

Table 3: Summary Identity Extensions
  Methodology Examples
Anonymous Address Identity Traffic Proxy VPN, TOR, ODoH
  Source Address Rollover SLAAC
  Private Address Spaces ULA
  Address Translation NAT
  Separate device from locator identifier EIBP, LISP
Authenticated Address Identity Self-certified Addresses CGA
  Third party granted addresses DHCP-Option

5.3. Semantic Extensions

Extensions in this subsection try extending the property described in Section 3.3, i.e., limited address semantic support.

As explained in Section 3.2, IP addresses carry both locator and identification semantic. Some efforts exist that try to separate these semantics either in different address spaces or through different address formats. Beyond just identification, location, and the fixed address size, other efforts extended the semantic through existing or additional header fields (or header options) outside the Internet address.

How much unique and globally routable an address should be? With the effect of centralization, edges communicate with (rather) local DCs, hence a unique address globally routable is not a requirement anymore. There is no need to use globally unique addresses all the time for communication, however, there is the need of having a unique address as a general way to communicate to any connected entity without caring what transmission networks the packets traverse.

5.3.1. Extended Address Semantics Description

Several extensions have been developed to extend beyond the limited IPv6 semantics. Those approaches may include to apply structure to the address, utilize specific prefixes, or entirely utilize the IPv6 address for different semantics, while re-encapsulating the original packet to restore the semantics in another part of the network. For instance, structured addresses have the capability to introduce delimiters to identify semantic information in the header, therefore not constraining any semantic by size limitations of the address fields.

We note here that extensions often start out as being proposed as an extended header semantic, while standardization may drive the solution to adopt an approach to accommodate their semantic within the limitations of an IP address. This section does include examples of this kind. Methodology
Semantic prefixes:

Semantic prefixes are used to separate the IPv6 address space. Through this, new address families, such as for information-centric networking [CAROFIGLIO19], service routing or other semantically rich addressing, can be defined, albeit limited by the prefix length and structure as well as the overall length limitation of the IPv6 address.

Separate device/resource from locator identifier:

The option to use separate namespaces for the device address would offer more freedom for the use of different semantics. For instance, the static binding of IP addresses to servers creates a strong binding between IP addresses and service/resources, which may be a limitation for large Content Distribution networks (CDNs) [FAYED21].

  • As an extreme form of separating resource from locator identifier, recent engineering approaches, described in [FAYED21], decouple web service (semantics) from the routing address assignments by using virtual hosting capabilities, thereby effectively mapping possibly millions of services onto a single IP address.

Structured addressing:

One approach to address the routing challenges faced in the Internet is the use of structured addresses, e.g., to void the need for routing protocols. Benefits of this approach can be significant, with the structured addresses capturing the relative physical or virtual position of routers in the network as well as being variable in length. Key to the approach, however, is that the structured addresses capturing the relative physical or virtual position of routers in the network, or networks in an internetwork may not fit within the fixed and limited IP address length (cf., Section 5.1.2). Other structured approaches may be the use of application-specific structured binary components for identification, generalizing URL schema used for HTTP-level communication but utilized at the network level for traffic steering decisions.

Localized forwarding semantics:

Layer 2 hardware, such as SDN switches, are limited to the use of specific header fields for forwarding decisions. Hence, devising new localized forwarding mechanisms may be based on re-using differently existing header fields, such as the IPv6 source/destination fields, to achieve the desired forwarding behavior, while encapsulating the original packets in order to be restored at the local forwarding network boundary. Networks in those solutions are limited by the size of the utilized address field, e.g., 256 bits for IPv6, thereby limiting the way such techniques could be used.

5.3.2. Existing or Extended Header Semantics Description

While the former sub-section explored extended address semantic, thereby limiting any such extended semantic with that of the existing IPv6 semantic and length, additional semantics may also be placed into the header of the packet or the packet itself, utilized for the forwarding decision to the appropriate endpoint according to the extended semantic.

Reasons for embedding such new semantics may be related to traffic engineering since it has long been shown that the IP address itself is not enough to steer traffic properly since the IP address itself is not semantically rich enough to adequately describe the forwarding decision to be taken in the network, not only impacting where the packet will need to go, but also how it will need to be sent. Methodology
In-Header extensions:

One way to add additional semantics besides the address fields is to use other fields already present in the header.

Headers option extensions:

Another mechanism to add additional semantics is to actually add additional fields, e.g., through Header Options in IPv4 or through Extension Headers in IPv6.

Re-encapsulation extension:

A more radical approach for additional semantics is the use of a completely new header that is designed so to carry the desired semantics in an efficient manner (often as a shim header).

Structured addressing:

Similar to the methodology that structures addresses within the limitations of the IPv6 address length, outlined in the previous sub-sections, structured addressing can also be applied within existing or extended header semantics, e.g., utilizing a dedicated (extension) header to carry the structured address information.

Localized forwarding semantics:

This set of solutions applies capabilities of newer (programmable) forwarding technology, such as [BOSSHART14], to utilize any header information for a localized forwarding decision. This removes any limitation to use existing header or address information for embedding a new address semantic into the transferred packet.

5.3.3. Examples

Table 4, summarize the methodologies and lists examples of semantic extensions.

Table 4: Summary Semantic Extensions
  Methodology Examples
Utilizing Extended Address Semantics Semantic prefixes HICN
  Separate device from locator identifier EIBP, ILNP, LISP, HIP
  Structured addressing EIBP, ILNP
  Localized forwarding semantics REED
Utilizing Existing or Extended Header Semantics In-Header extensions DetNet
  Headers option extensions SHIM6, SRv6, HIP
  Re-encapsulation extension VxLAN, ICNIP
  Structured addressing EIBP
  Localized forwarding semantics REED

5.4. IP Addressing Extensions Overall Summary

The following Table 5 describes the objectives of the extensions discussed in this memo with respect to the properties of Internet addressing (Section 3). As summarized, extensions may aim to extend one property of the Internet addressing, or extend other properties at the same time.

Table 5: Relationship between Extensions and Internet Addressing
  Length Extension Identity Extension Semantic Extension
6LoWPAN ([RFC6282], [RFC7400], [BADENHOP15], [RFC8376], [RFC8724]) x    
ROHC [RFC5795] x    
EzIP [EZIP] x    
TOR [TOR]   x  
ODoH [RFC9230]   x  
SLAAC [RFC8981]   x  
CGA [RFC3972]   x x
NAT [RFC3083] x x  
CCNx names x x x
EIBP [SHENOY21] x x x
Geo addressing x   x
REED [REED16] x (with P4 [BOSSHART14])   x
DetNet [DETNETWG]   x  
Mobile IP [RFC6275]     x
SHIM6 [RFC5533]     x
SRv6 [RFC8402]     x
HIP [RFC7401]   x x
VxLAN [RFC7348]   x x
LISP ([RFC9300], [RFC8060])   x x
SFC [RFC7665]   x x

6. Concerns Raised by IP Addressing Extensions

While the extensions to the original Internet properties, discussed in Section 5, demonstrate the need of more flexibility in addressing, they also raise a number of concerns, which are discussed in the following sub-sections. To this end, the problems hereafter outlined link to the approaches to extensions summarized in Section 5.4. These considerations may not be present all the time and everywhere, since extensions are developed and deployed in different part of the Internet, which may worsen things.

6.1. Limiting Address Semantics

Many approaches changing the semantics of communication, e.g., through separating host identification from network node identification [RFC7401], separating the device identifier from the routing locator ([SHENOY21], [RFC9299]), or through identifying content and services directly [CAROFIGLIO19], are limited by the existing packet size and semantic constraints of IPv6, e.g., in the form of its source and destination network addresses.

While approaches such as ICNIP [I-D.trossen-icnrg-internet-icn-5glan] may override the addressing semantics, e.g., by replacing IPv6 source and destination information with path identification, a possible unawareness of endpoints still requires the carrying of other address information as part of the payload.

Also, the expressible service or content semantic may be limited, as in [CAROFIGLIO19] or the size of supported networks [REED16] due to relying on the limited bit positions usable in IPv6 addresses.

6.2. Complexity and Efficiency

Realizing the additional addressing semantics may introduce additional complexity. This is particularly a concern since those additional semantics can be observed particularly at the edge of the Internet, utilizing the existing addressing semantic of the Internet to interconnect the domains that require those additional semantics.

Furthermore, any additional complexity often comes with an efficiency and cost penalty, particularly at the edge of the network, where resource constraints may play a significant role. Compression processes, taking [FITZEK05] as an example, require additional resources both for the sender generating the compressed header but also the gateway linking to the general Internet by re-establishing the full IP header.

Conversely, the performance requirements of core networks, in terms of packet processing speed, makes the accommodation of extensions to addressing often prohibitive. This is not only due to the necessary extra processing that is specific to the extension, but also due to the complexity that will need to be managed in doing so at significantly higher speeds than at the edge of the network. The observations on the dropping of packets with IPv6 extension headers in the real world is (partially) due to such an implementation complexity [RFC7872].

Another example for lowering the efficiency of packet forwarding is the routing in systems like Tor [TOR]. As detailed before, traffic in Tor, for anonymity purposes, should be handed over by at least three intermediates before reaching the destination. Frequent relaying enhances the privacy, however, because such kind of solutions are implemented at application level, they come at the cost of lower communication efficiency. May be a different privacy enhanced address semantic would enable efficient implementation of Tor-like solutions at network layer.

Repetitive Encapsulation:

Repetitive encapsulation is a concern since it bloats the packets size due to additional encapsulation headers. Addressing proposals such as those in [I-D.trossen-icnrg-internet-icn-5glan] utilize path identification within an alternative forwarding architecture that acts upon the provided path identification. However, due to the limitation of existing flow-based architectures with respect to the supported header structures (in the form of IPv4 or IPv6 headers), the new routing semantics are being inserted into the existing header structure, while repeating the original, sender-generated header structure, in the payload of the packet as it traverses the local domain, effectively doubling the per-packet header overhead.

  • The problem is also present in a number of solutions tackling different use-cases, e.g., mobility [I-D.ietf-lisp-mn], data center networking ([RFC8926], [RFC7348], [I-D.ietf-intarea-gue]), traffic engineering [RFC8986], and privacy ([TOR], [DANEZIS09]). Certainly, these solutions are able to avoid issues like path lengthening or privacy concerns, as described before, but they come at the price of multiple encapsulations that reduce the effective payload. This, not only hampers efficiency in terms of header-to-payload ratio, but also introduces 'encapsulation points', which in turn add complexity to the (often edge) network as well as fragility due to the addition of possible failure points; this aspect is discussed in further details in Section 6.4.

Compounding Concerns with Header Compression:

IP header overhead requires header compression in constrained environments, such as wireless sensor networks and IoT in general. Together with fragmentation, both tasks constitute significant energy consumption, as shown in [MESRINEJAD11], negatively impacting resource limited devices that often rely on battery for operation. Further, the reliance on the compression/decompression points creates a dependence on such gateways, which may be a problem for intermittent scenarios.

  • According to the implementation of contiki-ng [CONTIKI], an example of operating system for IoT devices, the source codes for 6LowPan requires at least 600Kb to include a header compression process. In certain use cases, such requirement can be an obstacle for extremely constrained devices, especially for the RAM and energy consumption.

Introducing Path Stretch:

Mobile IP [RFC6275], which was designed for connection continuity in the face of moving endpoints, is a typical case for path stretch. Since traffic must follow a triangular route before arriving at the destination, such detour routing inevitably impacts transmission efficiency as well as latency.

Complicating Traffic Engineering:

While many extensions to the original IP address semantic target to enrich the decisions that can be taken to steer traffic, according to requirements like QoS, mobility, chaining, compute/network metrics, flow treatment, path usage, etc., the realization of the mechanisms as individual solutions likely complicates the original goal of traffic engineering when individual solutions are being used in combination. Ultimately, this may even prevent the combined use of more than one mechanism and/or policy with a need to identify and prevent incompatibilities of mechanisms. Key here is not the concerns arising from using conflicting traffic engineering policies, rather conflicting realizations of policies that may well generally work well alongside ([CANINI15], [CURIC18]).

  • This not only increases fragility, as discussed separately in Section 6.4, but also requires careful planning of which mechanisms to use and in which combination, likely needing human-in-the-loop approaches alongside possible automation approaches for the individual solutions.

6.3. Security

The properties described in Section 5 have, obviously, also consequences in terms of security and privacy related concerns, as already mentioned in other parts of this document.

For instance, in the effort of being somehow backward compatible, HIP [RFC7401] uses a 128-bit Host Identity, which may be not sufficiently cryptographically strong in the future, because of the limited size (future computational power may erode 128-bit security). Similarly, CGA [RFC3972] also aligns to the 128-bit limit, but may use only 59 bits of them, hence, the packet signature may not be sufficiently robust to attacks [I-D.rafiee-6man-cga-attack].

IP addresses, even temporary ones meant to protect privacy, have been long recognized as a 'Personal Identification Information' that allows even to geolocate the communicating endpoints [RFC8280]. The use of temporary addresses provides sufficient privacy protection only if the renewal rate is high [I-D.gont-v6ops-ipv6-addressing-considerations]. However, this may raise some issues, like the large overhead due to the Duplicate Address Detection, the impact on the Neighbor Discovery mechanism, in particular the cache, which can even lead to communication disruption. With such drawbacks, the extensions may even lead to defeat the target, actually lowering security rather than increasing it.

The introduction of alternative addressing semantics has also been used to help in (D)DoS attacks mitigation. This leverages on changing the service identification model so to avoid topological information exposure, making the potential disruptions likely remain limited [HAO21]. However, this increased robustness to DDoS comes at the price of important communication setup latency and fragility, as discussed next.

6.4. Fragility

From the extensions discussed in Section 5, it is evident that having alternative or additional address semantic and formats available for making routing as well as forwarding decisions dependent on these, is common place in the Internet. This, however, adds many extension-specific translation/adaptation points, mapping the semantic and format in one context into what is meaningful in another context, but also, more importantly, creating a dependency towards an additional component, often without explicit exposure to the endpoints that originally intended to communicate.

For instance, the re-writing of IP addresses to facilitate the use of private address spaces throughout the public Internet, realized through network address translators (NATs), conflicts with the end-to-end nature of communication between two endpoints. Additional (flow) state is required at the NAT middle-box to smoothly allow communication, which in turn creates a dependency between the NAT and the end-to-end communication between those endpoints, thus increasing the fragility of the communication relation.

A similar situation arises when supporting constrained environments through a header compression mechanism, adding the need for, e.g., a ROHC [RFC5795] element in the communication path, with communication-related compression state being held outside the communicating endpoints. Failure will introduce some inefficiencies due to context regeneration, which may affect the communicating endpoints, increasing fragility of the system overall.

Such translation/adaptation between semantic extensions to the original 'semantic' of an IP address is generally not avoidable when accommodating more than a single universal semantic. However, the solution-specific nature of every single extension is likely to noticeably increase the fragility of the overall system, since individual extensions will need to interact with other extensions that may be deployed in parallel, but were not designed taking into account such deployment scenario (cf., [I-D.ietf-intarea-tunnels]). Considering that extensions to traditional per-hop-behavior (based on IP addresses) can essentially be realized over almost 'any' packet field, the possible number of conflicting behaviors or diverging interpretation of the semantic and/or content of such fields, among different extensions, may soon become an issue, requiring careful testing and delineation at the boundaries of the network within which the specific extension has been realized.

6.5. Summary of Concerns

Table 6, derived from the previous sections, summarizes the concerns discussed in this section related to each extension listed in Section 5.4. While each extension involves at least one concern, some others, like ICNIP [I-D.trossen-icnrg-internet-icn-5glan], may create several at the same time.

Table 6: Concerns in Extensions to Internet Addressing
  Limiting Address Semantics Complexity and Efficiency Security Fragility
6LoWPAN   x   x
ROHC   x   x
EzIP   x    
TOR   x   x
ODoH   x    
SLAAC   x    
CGA x   x  
NAT   x   x
HICN x      
ICNIP x x    
CCNx name x      
EIBP       x
Geo addressing x     x
REED x      
DetNet   x    
Mobile IP   x   x
SHIM6       x
SRv6       x
HIP     x x
VxLAN   x    
LISP   x   x
SFC   x   x

7. Discussion

The examples of extensions discussed in Section 5 to the original Internet addressing scheme show that extensibility beyond the original model (and its underlying per-hop behavior) is a desired capability for networking technologies and has been so for a long time. Generally, we can observe that those extensions are driven by the requirements of stakeholders, derived from the aforementioned problems and communication scenarios, thus, expecting a desirable extended functionality from the introduction of the specific extension. If interoperability is required, those extensions require standardization of possibly new fields, new semantics as well as (network and/or end system) operations alike.

This points to the conclusion that the existence of the many extensions to the original Internet addressing is clear evidence for wanting to develop evolution paths over time by the wider Internet community, each of which come with a raft of issues that we need to deal with daily. This makes it desirable to develop an architectural and, more importantly, a sustainable approach to make Internet addressing extensible in order to capture the many new use cases that will still be identified for the Internet to come.

This is not to 'second guess' the market and its possible evolution, but to outline clear features from which to derive clear principles for a design. Any such design must not skew the technical capabilities of addressing to the current economic situation of the Internet and its technical realization, e.g., being a mere ephemeral token for accessing PoP-based services (as indicated in related arch-d mailing list discussions), since this bears the danger of locking down innovation capabilities as an outcome of those technical limitations introduced. Instead, addressing must be aligned with enabling the model of permissionless innovation that the IETF has been promoting, ultimately enabling the serendipity of new applications that has led to many of those applications we can see in the Internet today.

Having a more systematic approach, rather than point extensions, would allow the Internet community to identify an overall evolutionary path able to accommodate existing and future use cases, without disruptive solutions breaking existing deployments, rather with a well-thought out set of incremental steps.

An architectural evolution of the IP addressing model may bring clear benefits in various scenarios. Examples of such benefits are provided hereafter, for a short sample of use cases. An extensive discussion about these use cases can be found in Appendix B.

Finally, it is important to remark that any change in the addressing, hence at the data plane level, leads to changes and challenges at the control plane level, i.e., routing. The latter is an even harder problem than just addressing and might need more research efforts that are beyond what is discussed in this document, which focuses solely on the data plane.

8. Looking Forward

At this stage, this document does not provide a definite answer nor does it propose or promote specific solutions to the issues it portrays. Instead, this document captures the discussion on the perceived needs for addressing, with the possibility to fundamentally re-think the addressing in the Internet beyond the objectives of IPv6, in order to provide the flexibility to suitably support the many new forms of communication that will emerge.

It has been observed during the interactions of this wider exercise within the IETF that the considerations documented in this memo, with the various extension-specific solutions, have the merit to capture the views and opinions of a large part of the IETF community at the time of writing this document.

Although some of the discussions hinted at "something should be done", those same discussions never converged to answer the "what should be done" aspect. However, we assert from experiences in the past that the community may at some point in the future re-open discussions surrounding the IP addressing model and its possible evolution.

For the reason to possibly provide a useful starting point, thus to help jump start any initial future discussion, this document provides an archive of those specific discussions in the early 2020s as a recollection of discussions held at that point in time.

We hope that any such future discussions and the possible input from the recollections in this document, may bring the IETF community to converge on concrete actions to be done.

9. Security Considerations

The present memo does not introduce any new technology and/or mechanism and as such does not introduce any new security threat to the TCP/IP protocol suite.

As an additional note, and as discussed in this document, security and privacy aspects were not considered as part of the key properties for Internet addressing, which led to the introduction of a number of extensions intending to fix those gaps. The analysis presented in this memo (non-exhaustively) shows those concerns are either solved in an ad-hoc manner at application level, or at transport layer, while at network level only few extensions tackling specific aspects exist, albeit often with limitations due to the adherence to the Internet addressing model and its properties.

10. IANA Considerations

This document does not include any IANA request.


Thanks to all the people that shared insightful comments both privately to the authors as well as on various mailing list, especially on the INTArea Mailing List. Thanks as well, for the interesting discussions, to Carsten Borman, Brian E. Carpenter, and Eric Vyncke.

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Carpenter, B., "Internet Transparency", RFC 2775, DOI 10.17487/RFC2775, , <>.
Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, DOI 10.17487/RFC2865, , <>.
Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, , <>.
Woundy, R., "Baseline Privacy Interface Management Information Base for DOCSIS Compliant Cable Modems and Cable Modem Termination Systems", RFC 3083, DOI 10.17487/RFC3083, , <>.
Droms, R., Ed. and W. Arbaugh, Ed., "Authentication for DHCP Messages", RFC 3118, DOI 10.17487/RFC3118, , <>.
Aura, T., "Cryptographically Generated Addresses (CGA)", RFC 3972, DOI 10.17487/RFC3972, , <>.
Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, , <>.
Droms, R. and J. Schnizlein, "Remote Authentication Dial-In User Service (RADIUS) Attributes Suboption for the Dynamic Host Configuration Protocol (DHCP) Relay Agent Information Option", RFC 4014, DOI 10.17487/RFC4014, , <>.
Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast Addresses", RFC 4193, DOI 10.17487/RFC4193, , <>.
Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, , <>.
Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, , <>.
Bagnulo, M. and J. Arkko, "Cryptographically Generated Addresses (CGA) Extension Field Format", RFC 4581, DOI 10.17487/RFC4581, , <>.
Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and Goals", RFC 4919, DOI 10.17487/RFC4919, , <>.
Bagnulo, M. and J. Arkko, "Support for Multiple Hash Algorithms in Cryptographically Generated Addresses (CGAs)", RFC 4982, DOI 10.17487/RFC4982, , <>.
Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M. Kozuka, "Stream Control Transmission Protocol (SCTP) Dynamic Address Reconfiguration", RFC 5061, DOI 10.17487/RFC5061, , <>.
Leung, K., Dommety, G., Narayanan, V., and A. Petrescu, "Network Mobility (NEMO) Extensions for Mobile IPv4", RFC 5177, DOI 10.17487/RFC5177, , <>.
Turner, S., "CMS Symmetric Key Management and Distribution", RFC 5275, DOI 10.17487/RFC5275, , <>.
HomChaudhuri, S. and M. Foschiano, "Cisco Systems' Private VLANs: Scalable Security in a Multi-Client Environment", RFC 5517, DOI 10.17487/RFC5517, , <>.
Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming Shim Protocol for IPv6", RFC 5533, DOI 10.17487/RFC5533, , <>.
Sandlund, K., Pelletier, G., and L-E. Jonsson, "The RObust Header Compression (ROHC) Framework", RFC 5795, DOI 10.17487/RFC5795, , <>.
Perkins, C., Ed., "IP Mobility Support for IPv4, Revised", RFC 5944, DOI 10.17487/RFC5944, , <>.
DeKok, A., Ed. and G. Weber, "RADIUS Design Guidelines", BCP 158, RFC 6158, DOI 10.17487/RFC6158, , <>.
Ford, A., Raiciu, C., Handley, M., Barre, S., and J. Iyengar, "Architectural Guidelines for Multipath TCP Development", RFC 6182, DOI 10.17487/RFC6182, , <>.
Thaler, D., "Evolution of the IP Model", RFC 6250, DOI 10.17487/RFC6250, , <>.
Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, , <>.
Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, DOI 10.17487/RFC6282, , <>.
Tsirtsis, G., Park, V., Narayanan, V., and K. Leung, "Dynamic Prefix Allocation for Network Mobility for Mobile IPv4 (NEMOv4)", RFC 6626, DOI 10.17487/RFC6626, , <>.
Atkinson, RJ. and SN. Bhatti, "Identifier-Locator Network Protocol (ILNP) Architectural Description", RFC 6740, DOI 10.17487/RFC6740, , <>.
Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., Morris, J., Hansen, M., and R. Smith, "Privacy Considerations for Internet Protocols", RFC 6973, DOI 10.17487/RFC6973, , <>.
Bormann, C., Ersue, M., and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, , <>.
Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, , <>.
Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, , <>.
Laganier, J. and F. Dupont, "An IPv6 Prefix for Overlay Routable Cryptographic Hash Identifiers Version 2 (ORCHIDv2)", RFC 7343, DOI 10.17487/RFC7343, , <>.
Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger, L., Sridhar, T., Bursell, M., and C. Wright, "Virtual eXtensible Local Area Network (VXLAN): A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 Networks", RFC 7348, DOI 10.17487/RFC7348, , <>.
Bormann, C., "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, , <>.
Moskowitz, R., Ed., Heer, T., Jokela, P., and T. Henderson, "Host Identity Protocol Version 2 (HIPv2)", RFC 7401, DOI 10.17487/RFC7401, , <>.
Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S., Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software-Defined Networking (SDN): Layers and Architecture Terminology", RFC 7426, DOI 10.17487/RFC7426, , <>.
Liu, D., Ed., Zuniga, JC., Ed., Seite, P., Chan, H., and CJ. Bernardos, "Distributed Mobility Management: Current Practices and Gap Analysis", RFC 7429, DOI 10.17487/RFC7429, , <>.
Pentikousis, K., Ed., Ohlman, B., Corujo, D., Boggia, G., Tyson, G., Davies, E., Molinaro, A., and S. Eum, "Information-Centric Networking: Baseline Scenarios", RFC 7476, DOI 10.17487/RFC7476, , <>.
Halpern, J., Ed. and C. Pignataro, Ed., "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, , <>.
Gont, F., Linkova, J., Chown, T., and W. Liu, "Observations on the Dropping of Packets with IPv6 Extension Headers in the Real World", RFC 7872, DOI 10.17487/RFC7872, , <>.
Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060, , <>.
Farinacci, D. and B. Weis, "Locator/ID Separation Protocol (LISP) Data-Plane Confidentiality", RFC 8061, DOI 10.17487/RFC8061, , <>.
Mariager, P., Petersen, J., Ed., Shelby, Z., Van de Logt, M., and D. Barthel, "Transmission of IPv6 Packets over Digital Enhanced Cordless Telecommunications (DECT) Ultra Low Energy (ULE)", RFC 8105, DOI 10.17487/RFC8105, , <>.
Lynn, K., Ed., Martocci, J., Neilson, C., and S. Donaldson, "Transmission of IPv6 over Master-Slave/Token-Passing (MS/TP) Networks", RFC 8163, DOI 10.17487/RFC8163, , <>.
Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, , <>.
ten Oever, N. and C. Cath, "Research into Human Rights Protocol Considerations", RFC 8280, DOI 10.17487/RFC8280, , <>.
Farrell, S., Ed., "Low-Power Wide Area Network (LPWAN) Overview", RFC 8376, DOI 10.17487/RFC8376, , <>.
Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, , <>.
Hoffman, P. and P. McManus, "DNS Queries over HTTPS (DoH)", RFC 8484, DOI 10.17487/RFC8484, , <>.
Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based Forwarding Plane for Service Function Chaining", RFC 8595, DOI 10.17487/RFC8595, , <>.
Mosko, M., Solis, I., and C. Wood, "Content-Centric Networking (CCNx) Messages in TLV Format", RFC 8609, DOI 10.17487/RFC8609, , <>.
Trossen, D., Purkayastha, D., and A. Rahman, "Name-Based Service Function Forwarder (nSFF) Component within a Service Function Chaining (SFC) Framework", RFC 8677, DOI 10.17487/RFC8677, , <>.
Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC. Zuniga, "SCHC: Generic Framework for Static Context Header Compression and Fragmentation", RFC 8724, DOI 10.17487/RFC8724, , <>.
Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header (SRH)", RFC 8754, DOI 10.17487/RFC8754, , <>.
Rahman, A., Trossen, D., Kutscher, D., and R. Ravindran, "Deployment Considerations for Information-Centric Networking (ICN)", RFC 8763, DOI 10.17487/RFC8763, , <>.
Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed., "Geneve: Generic Network Virtualization Encapsulation", RFC 8926, DOI 10.17487/RFC8926, , <>.
Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S. Bryant, "Deterministic Networking (DetNet) Data Plane: IP", RFC 8939, DOI 10.17487/RFC8939, , <>.
Gont, F., Krishnan, S., Narten, T., and R. Draves, "Temporary Address Extensions for Stateless Address Autoconfiguration in IPv6", RFC 8981, DOI 10.17487/RFC8981, , <>.
Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer, D., Matsushima, S., and Z. Li, "Segment Routing over IPv6 (SRv6) Network Programming", RFC 8986, DOI 10.17487/RFC8986, , <>.
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, , <>.
Card, S., Ed., Wiethuechter, A., Moskowitz, R., and A. Gurtov, "Drone Remote Identification Protocol (DRIP) Requirements and Terminology", RFC 9153, DOI 10.17487/RFC9153, , <>.
Kinnear, E., McManus, P., Pauly, T., Verma, T., and C.A. Wood, "Oblivious DNS over HTTPS", RFC 9230, DOI 10.17487/RFC9230, , <>.
Hinden, R. and G. Fairhurst, "IPv6 Minimum Path MTU Hop-by-Hop Option", RFC 9268, DOI 10.17487/RFC9268, , <>.
Cabellos, A. and D. Saucez, Ed., "An Architectural Introduction to the Locator/ID Separation Protocol (LISP)", RFC 9299, DOI 10.17487/RFC9299, , <>.
Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A. Cabellos, Ed., "The Locator/ID Separation Protocol (LISP)", RFC 9300, DOI 10.17487/RFC9300, , <>.
Farinacci, D., Maino, F., Fuller, V., and A. Cabellos, Ed., "Locator/ID Separation Protocol (LISP) Control Plane", RFC 9301, DOI 10.17487/RFC9301, , <>.
Hou, J., Liu, B., Hong, Y-G., Tang, X., and C. Perkins, "Transmission of IPv6 Packets over Power Line Communication (PLC) Networks", RFC 9354, DOI 10.17487/RFC9354, , <>.
Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov, "DRIP Entity Tag (DET) for Unmanned Aircraft System Remote ID (UAS RID)", RFC 9374, DOI 10.17487/RFC9374, , <>.
Shenoy, N., Chandraiah, S., and P. Willis, "A Structured Approach to Routing in the Internet", 2021 IEEE 22nd International Conference on High Performance Switching and Routing (HPSR), DOI 10.1109/hpsr52026.2021.9481818, , <>.
IETF 112 Side Meetings, "Internet Addressing: problems and gap analysis", , <>.
"Deutsche Telekom tests TeraStream, the network of the future, in Croatia", n.d., <>.
"The Tor Project", n.d., <>.
Trossen, D., Sarela, M., and K. Sollins, "Arguments for an information-centric internetworking architecture", ACM SIGCOMM Computer Communication Review vol. 40, no. 2, pp. 26-33, DOI 10.1145/1764873.1764878, , <>.
Voigt, P. and A. von dem Bussche, "The EU General Data Protection Regulation (GDPR)", Springer International Publishing book, DOI 10.1007/978-3-319-57959-7, , <>.
Wang, P., Zhang, J., Zhang, X., Yan, Z., Evans, B., and W. Wang, "Convergence of Satellite and Terrestrial Networks: A Comprehensive Survey", IEEE Access vol. 8, pp. 5550-5588, DOI 10.1109/access.2019.2963223, , <>.
Wion, A., Bouet, M., Iannone, L., and V. Conan, "Distributed Function Chaining with Anycast Routing", Proceedings of the 2019 ACM Symposium on SDN Research, DOI 10.1145/3314148.3314355, , <>.

Appendix A. Desirable Networking Features

The present section outlines the general features that are desirable in a networked system at large, i.e., not specific to any application/usage. Such list is a "by-product" of the addressing discussion and completely created through mail exchanges.

  1. Always-On: The world is getting more and more connected, leading to being connected to the Internet, anywhere, by any technology (e.g., cable, fiber, or radio), even simultaneously, "all the time", and, most importantly, automatically (without any switch turning). However, when defining "all the time" there is a clear and important difference to be made between availability and reliability vs "desired usage". In other words, "always on" can be seen as a desirable perception at the end user level or as a characteristic of the underlying system. From an end user perspective, clearly the former is of importance, not necessarily leading to an "always on" system notion but instead "always-app-available", merely requiring the needed availability and reliability to realize the perception of being "always on" (e.g., for earthquake alerts), possibly complemented by app-specific methods to realize the "always on" perception (e.g., using local caching rather than communication over the network).
  2. Transparency: Being agnostic with respect to local domains network protocols (Bluetooth, ZigBee, Thread, Airdrop, Airplay, or any others) is key to provide an easy and straightforward method for contacting people and devices without any knowledge of network issues, particularly those specific to network-specific solutions. While having a flexible addressing model that accommodates a wide range of use cases is important, the centrality of the IP protocol remains key as a mean to provide global connectivity.
  3. Multi-homing: Seamless multi-homing capability for the host is key to best use the connectivity options that may be available to an end user, e.g., for increasing resilience in cases of failures of one available option. Protocols like LISP, SHIM6, QUIC, MPTCP, SCTP (to cite a few) have been successful at providing this capability in an incremental way, but too much of that capability is realized within the specific application domain, making it hard to leverage across all applications. While today each transport protocol has its own way to perform multi-address discovery, the network layer should provide the multi-homing feature (e.g., SHIM6 can be used to discover all addresses on both ends), and then leave the address selection to the transport. With that, multi-address discovery remains a network feature exposed to the upper layers. This may also mean to update the Socket API (which may be actually the first thing to do), which does not necessarily mean to expose more network details to the applications but instead be more address agnostic, yet, more expressive.
  4. Mobility: A lot of work has been put in MobileIP ([RFC5944], [RFC6275]) to provide seamless and lossless communications for moving nodes (vehicle, satellites). However, it has never been widely deployed for several reasons, like complexity of the protocol and the fact that the problem has often been tackled at higher layers, with applications resilient to address changes. However, similar to multi-homing, solving the problem at higher layers means that each and every transport protocol and application have their own way to deal with mobility, leading to similar observations as those for the previous multi-homing aspect.
  5. Security and Privacy: The COVID-19 pandemic has boosted end users' desire to be protected and protect their privacy. The balance among privacy, security, and accountability is not simple to achieve. There exist different views on what those properties should be, however the network should provide the means to provide what is felt as the best trade-off for the specific use case.
  6. Performance: While certainly desirable, "performance" is a complex issue that depends on the objectives of those building for but also paying for performance. Examples are (i) speed (shorter paths/direct communications), (ii) bandwidth (10petabit/s for a link), (iii) efficiency (less overlays/encapsulations), (iv) high efficacy or sustainability (avoid waste). From an addressing perspective, length/format/semantics that may adapt to the specific use case (e.g. use short addresses for low power IoT, or, where needed, longer for addresses embedding certificates for strong authentication, authorization and accountability) may contribute to the performance aspects that end users desire, such as reducing waste through not needed encapsulation or needed conversion at network boundaries.
  7. Availability, Reliability, Predictability: These three properties are important to enable wide-range of services and applications according to the desired usage (cf. point 1).
  8. Do not do harm: Access to the Internet is considered a human right [RFC8280]. Access to and expression through it should align with this core principle. This issue transcends through a variety of previously discussed 'features' that are desired, such as privacy, security but also availability and reliability. However, lifting the feature of network access onto a basic rights level also brings in the aspect of "do not do harm" through the use of the Internet with respect to wider societal objectives. Similar to other industries, such as electricity or cars, preventing harm usually requires an interplay of commercial, technological, and regulatory efforts, such as the enforcement of seat belt wearing to reduce accident death. As a first step, the potential harmfulness of a novel method must be recognized and weighted against the benefits of its introduction and use. One increasingly important consideration in the technology domain is "sustainability" of resource usage for an end user's consumption of and participation in Internet services. As an example, Distributed Ledger Technologies (DLT) are seen as an important tool for a variety of applications, including Internet decentralization ([DINRG]). However, the non-linear increase in energy consumption means that extending proof-of-work systems to the entire population of the planet would not only be impractical but also possibly highly wasteful, not just at the level of computation but also communication resource usage [I-D.trossen-rtgwg-impact-of-dlts]. This poses the question on how novel methods for addressing may improve on sustainability of such technologies, particularly if adopted more widely.
  9. Maximum Transmission Unit (MTU): One long standing issue in the Internet is related to the MTU and how to discover the path MTU in order to avoid fragmentation ([RFC9268], [I-D.templin-6man-aero]). While it makes sense to always leverage as much performance from local systems as possible, this should come without sacrificing the ability to communicate with all systems. Having a solid solution to solve the issue would make the overall interconnection of systems more robust.

Appendix B. IP Addressing Extensions driven by Use-Cases

Over the years, a plethora of extensions has been proposed in order to move beyond the native properties of IP addresses. The development of those extensions can be interpreted as attempts, in a limited scope, to go beyond the original properties of Internet addressing and desired new capabilities that those developing the extensions identified as being missing and yet needed and desirable.

The following sub-sections provide a more detailed and in-depth discussion about IP Addressing Extensions dvelopped to cope with the specific requirements of the use cases listed in Section 4.

B.1. Communication in Constrained Environments

In a number of communication scenarios, such as those encountered in the Internet of Things (IoT), a simple, communication network demanding minimal resources is required, allowing for a group of IoT network devices to form a network of constrained nodes, with the participating network and end nodes requiring as little computational power as possible and having small memory requirements in order to reduce the total cost of ownership of the network.Furthermore, in the context of industrial IoT, real-time requirements and scalability make IP technology not naturally suitable as communication technology ([OCADO]).

In the context of IoT, there are various technologies that allow to connect small objects. In addition to IEEE 802.15.4, i.e., Low-Rate Wireless Personal Area Network [IEEE-802.15.4-LR], several limited domains exist through utilizing link layer technologies such as Bluetooth Low Energy (BLE) [BLE], Digital European Cordless Telecommunications (DECT) - Ultra Low Energy (ULE) [DECT-ULE], Master-Slave/Token-Passing (MS/TP) [BACnet], Near-Field-Communication (NFC) [ECMA-340], and Power Line Communication (PLC) [IEEE-1901.1].

The end-to-end principle (detailed in [RFC2775]) requires IP addresses (e.g., IPv6 [RFC8200]) to be used on such constrained nodes networks, allowing IoT devices using multiple communication technologies to talk on the Internet. Often, devices located at the edge of constrained networks act as gateway devices, usually performing header compression ([RFC4919]). To ensure security and reliability, multiple gateways must be deployed. IoT devices on the network must select one of those gateways for traffic passthrough by the devices on the (limited domain) network.

Given the constraints imposed on the computational and possibly also communication technology, the usage of a single addressing semantic in the form of a 128-bit endpoint identifier, i.e., IPv6 address, may pose a challenge when operating such networks.

Another type of (differently) constrained environment is an aircraft, which encompasses not only passenger communication but also the integration of real-time data exchange to ensure that processes and functions in the cabin are automatically monitored or actuated. For aircraft networks, the goal is to be able to send and receive information reliably and seamlessly. From this perspective, the medium with which these packets of information are sent is of little consequence so long as there is a level of determinism to it. However, there is currently no effective method in implementing wireless inter- and intra-communications between all subsystems. The emerging wireless sensor network technology in commercial applications such as smart thermostat systems, and smart washer/dryer units could be transposed onto aircraft and fleet operations. The proposal for having an Wireless Avionics Intra-Communications (WAIC) system promises reduction in the complexity of electrical wiring harness design and fabrication, reduction in wiring weight, increased configuration, and potential monitoring of otherwise inaccessible moving or rotating aircraft parts. Similar to the IoT concept, WAIC systems consist of short-range communications and are a potential candidate for passenger entertainment systems, smoke detectors, engine health monitors, tire pressure monitoring systems, and other kinds of aircraft maintenance systems.

While there are still many obstacles in terms of network security, traffic control, and technical challenges, future WAIC can enable real-time seamless communications between aircraft and between ground teams and aircraft as opposed to the discrete points of data leveraged today in aircraft communications. For that, WAIC infrastructure should also be connected to outside IP based networks in order to access edge/cloud facilities for data storage and mining.

However, the restricted capacity (energy, communication) of most aircraft devices (e.g. sensors) and the nature of the transmitted data – periodic transmission of small packets – may pose some challenges for the usage of a single addressing semantic in the form of a 128-bit endpoint identifier, i.e., an IPv6 address. Moreover, most of the aircraft applications and services are focused on the data (e.g. temperature of gas tank on left wing) and not on the topological location of the data source. This means that the current topological location semantic of IP addresses is not beneficial for aircraft applications and services.

B.2. Communication within Dynamically Changing Topologies

Communication may occur over networks that exhibit dynamically changing
topologies. One such example is that of satellite networks, providing global Internet connections through a combination of inter-satellite and ground station communication. With the convergence of space-based and terrestrial networks, users can experience seamless broadband access, e.g., on cruise ships, flights, and within cars, often complemented by and seamlessly switching between Wi-Fi, cellular, or satellite based networks at any time [WANG19].

The satellite network service provider will plan the transmission path of user traffic based on the network coverage, satellite orbit, route, and link load, providing potentially high-quality Internet connections for users in areas that are not, or hard to be, covered by terrestrial networks. With large scale LEO (Low Earth Orbit) satellites, the involved topologies of the satellite network will be changing constantly while observing a regular flight pattern in relation to other satellites and predictable overflight patterns to ground users [CHEN21].

Although satellite bearer services are capable of transporting IPv4 and IPv6 [CCSDS-702.1-B-1], as well as associated protocols such as IP Multicast, DNS services and routing information, no IP functionality is implemented on-board the spacecraft, limiting the capability of leveraging for instance large scale satellite constellations.

One of the major constraints of deploying routing capability on board of a satellite is power consumption. Due to this, space routers may end up being intermittently powered up during a daytime sunlit pass. Another limitation of the first generation of IP routers in space was the lack of capability to remotely manage and upgrade software while in operation. Further, in order to reduce latency, which is the major impairment of satellite networks, there was a need of a networking solution able to perform in a scenario encompassing mobile devices with the capability of storing data, leading to a significant reduction of latency.

The limitations faced in early development of IP based satellite communication payloads, showed the need to develop a flexible networking solution that would enable delay tolerant communications in the presence of intermittent connectivity. Further, in order to reduce latency, which is the major impairment of satellite networks, there was a need of a networking solution able to perform in a scenario encompassing mobile devices with the capability of storing data, leading to a significant reduction of latency.

Moreover, due to the current IP addressing scheme and its focus on IP unicast addressing with extended deployment of IP multicast and some IP anycast, current deployments do not take advantage of the broadcast nature of satellite networks.

As a result of these constraints, the Consultative Committee for Space Data Systems (CCSDS) has produced its own communication standards distinct from those of the IETF. The conceptual model shares many similarities with the Open Systems Interconnection model, and individual CCSDS protocols often address comparable concerns to those standardized by the IETF, but always under the distinct concerns that connectivity may be intermittent, and while throughput rates may be high, so is latency.

Furthermore, the aerospace industry necessarily distinguishes strictly between "system" and "payload", largely for reasons of operational safety. The "system" here consists of aerospace and ground segments that together ensure the reliable operation of a craft within its designated space. At the same time, the "payload" describes any sensor or tool carried by a vehicle that is unrelated to craft operations, even if it may constitute a vital part of the overall mission.

The common practice today is to address system connectivity with the CCSDS protocol stack, while treating payload connectivity increasingly as an IP problem. It was to this end that [CCSDS-702.1-B-1] was developed. By layering IP within the CCSDS stack, it becomes just an opaque payload which may or may not be transmitted depending on current mission parameters. The distinct downside of this approach from a payload deployment perspective is that it is next to impossible in practice to route between an IP-based payload endpoints located on different satellites. The typical deployment scenarios treat each craft's payload and associated ground services as a private network, with no routing between them.

Networking platforms based on a name (data or service) based addressing scheme would bring several potential benefits to satellite network payloads aiming to tackle some of their major challenges, including high propagation delay.

Concerning the vehicular networks use-case, the communication may include Road Side Units (RSU) with the possibility to create ephemeral connections to those RSUs for the purpose of workload offloading, joint computation over multiple (vehicular) inputs, and other purposes [I-D.ietf-lisp-nexagon]. Communication here may exhibit a multi-hop nature, not just involving the vehicle and the RSU over a direct link.

Those topologies are naturally changing constantly due to the dynamic nature of the involved communication nodes.

The advent of Flying Ad-hoc NETworks (FANETs) has opened up an opportunity to create new added-value services [CHRIKI19]. Although these networks share common features with vehicular ad hoc networks, they present several unique characteristics such as energy efficiency, mobility degree, the capability of swarming, and the potential large scale of swarm networks.

Due to high mobility of FANET nodes, the network topology changes more frequently than in a typical vehicular ad hoc network. From a routing point of view, although ad-hoc reactive and proactive routing approaches can be used, there are other type of routing protocols that have been developed for FANETS, such as hybrid routing protocols and position based routing protocols, aiming to increase efficiency in large scale networks with dynamic topologies.

Both type of protocols challenge the current Internet addressing semantic: in the case of hybrid protocols, two different routing strategies are used inside and outside a network zone. While inside a zone packets are routed to a specific destination IP address, between zones, query packets are routed to a subset of neighbors as determined by a broadcast algorithm. In the case of position based routing protocol, the IP addressing scheme is not used at all, since packets are routed to a different identifier, corresponding to the geographic location of the destination and not its topological location. Hence, what is needed is to consolidate the geo-spatial addressing with that of a locator-based addressing in order to optimize routing policies across the zones.

Moreover most of the application/services deployed in FANETs tend to be agnostic of the topological location of nodes, rather focusing on the location of data or services. This distinction is even more important because is dynamic network such as FANET robust networking solutions may rely on the redundancy of data and services, meaning that they may be found in more than one device in the network. This in turn may bring into play a possible service-centric semantic for addressing the packets that need routing in the dynamic network towards a node providing said service (or content).

In the aforementioned network technologies, there is a significant difference between the high dynamics of the underlying network topologies, compared to the relative static nature of terrestrial network topology, as reported in [HANDLEY18]. As a consequence, the notion of a topological network location becomes restrictive in the sense that not only the relation between network nodes and user endpoint may change, but also the relation between the nodes that form the network itself. This may lead to the challenge of maintaining and updating the topological addresses in this constantly changing network topology.

In attempts to utilize entirely different semantics for the addressing itself, geographic-based routing, such as in [HUGHES03], has been proposed for MANETs (Mobile Ad-hoc NETworks) through providing geographic coordinates based addresses to achieve better routing performance, lower overhead, and lower latency [ABDALLAH16].

B.3. Communication among Moving Endpoints

When packet switching was first introduced, back in the 60s/70s, it was intended to replace the rigid circuit switching with a communication infrastructure that was more resilient to failures. As such, the design never really considered communication endpoints as mobile. Even in the pioneering ALOHA [KUO95] system, despite considering wireless and satellite links, the network was considered static (with the exception of failures and satellites, which fall in what is discussed in Appendix B.2). Ever since, a lot of efforts have been devoted to overcome such limitations once it became clear that endpoint mobility will become a main (if not THE main) characteristic of ubiquitous communication systems.

The IETF has for a long time worked on solutions that would allow extending the IP layer with mobility support. Because of the topological semantic of IP addresses, endpoints need to change addresses each time they visit a different network. However, because routing and endpoint identification is also IP address based, this leads to a communication disruption.

The lack of an efficient mobility management solution at network layer enabled the opportunity to involve the transport layer in mobility solutions, either by introducing explicit in-band signaling to allow for communicating IP address changes (e.g., in SCTP [RFC5061] and MPTCP [RFC6182]), or by introducing some form of connection ID that allows for identifying a communication independently from IP addresses (e.g., the connection ID used in QUIC [RFC9000]).

Concerning network layer only solutions, anchor-based Mobile IP mechanisms have been introduced ([RFC5177], [RFC6626] [RFC5944], [RFC5275]). Mobile IP is based on a relatively complex and heavy mechanism that makes it hard to deploy and it is not very efficient. Furthermore, it is even less suitable than native IP in constrained environments like the ones discussed in Appendix B.1.

Alternative approaches to Mobile IP often leverage the introduction of some form of overlay. LISP [RFC9299], by separating the topological semantic from the identification semantic of IP addresses, is able to cope with endpoint mobility by dynamically mapping endpoint identifiers with routing locators [I-D.ietf-lisp-mn]. This comes at the price of an overlay that needs its own additional control plane [RFC9301].

Similarly, the NVO3 (Network Virtualization Overlays) Working Group, while focusing on Data Center environments, also explored an overlay-based solution for multi-tenancy purposes, but also resilient to mobility since relocating Virtual Machines (VMs) is common practice. NVO3 considered for a long time several data planes that implement slightly different flavors of overlays ([RFC8926], [RFC7348], [I-D.ietf-intarea-gue]), but lacks an efficient control plane specifically tailored for DCs.

Alternative mobility architectures have also been proposed in order to cope with endpoint mobility outside the IP layer itself. The Host Identity Protocol (HIP) [RFC7401] introduced a new namespace in order to identify endpoints, namely the Host Identity (HI), while leveraging the IP layer for topological location. On the one hand, such an approach needs to revise the way applications interact with the network layer, by modifying the DNS (now returning an HI instead of an IP address) and applications to use the HIP socket extension. On the other hand, early adopters do not necessarily gain any benefit unless all communicating endpoints upgrade to use HIP. In spite of this, such a solution may work in the context of a limited domain.

Another alternative approach is adopted by Information-Centric Networking (ICN) [RFC7476]. By making content a first class citizen of the communication architecture, the "what" rather than the "where" becomes the real focus of the communication. However, as explained in the next sub-section, ICN can run either over the IP layer or completely replace it, which in turn can be seen as running the Internet and ICN as logically completely separated limited domains.

Unmanned Aircraft Systems (UAS) are examples of moving devices that require a stable mobility management scheme since they consist of a number of Unmanned Aerial Vehicles (UAV; or drones) subordinated to a Ground Control Station (GCS) [MAROJEVIC20]. The information produced by the different sensors and electronic devices available at each UAV is collected and processed by a software or hardware data acquisition unit, being transmitted towards the GCS, where it is inspected and/or analyzed. Analogously, control information transmitted from the GCS to the UAV enables the execution of control operations over the aircraft, such as changing the route planning or the direction pointed by a camera.

Drones may be classified into several distinct categories, with implications on regulatory requirements. Vehicles carrying people generally fall under manned aircraft regulations whether they manually or automatically piloted. At the opposite end of the spectrum, toy drones require Line-of-Sight operations.

In the middle there are a variety of specialized UAVs that, although may have redundant links to maintain communications in long-range missions (e.g., satellite), perform most of the communications with the GCS over wireless data links, e.g., based on a radio line-of-sight technology such as Wi-Fi or 3G/4G/5G. While in some scenarios, UAVs will operate always under the range of the same cellular base station, in missions with large range, UAVs will move between different cellular or wireless ground infrastructure, meaning that the UAV needs to upload its topological locator and re-start the ongoing communication sessions.

In particular, in Beyond Visual Line of Sight (BVLOS) operations, legal requirements may include the use of multiple redundant radio links (even employing different radio bands), but still require unique identification of the vehicle. This implies that some resolution mechanism is required that securely resolves drone identifiers to link locators.

To this end, Drone Remote Identification Protocol [I-D.ietf-drip-arch] uses hierarchical DRIP Entity Tags, which are hierarchical versions of Host Identity Tags, and thus compatible with HIP [RFC7401]. DRIP does not mandate the use of HIP, but suggests its use in several places. Using the mobility extensions of HIP provides for one way to ensure secure identifier resolution.

In addition to such connectivity considerations, data-centric communication plays an increasing role, where information is named and decoupled from its location, and applications/services operate over these named data rather than on host-to-host communications.

In this context, the Data Distribution Service ([ALMADANI20]) has emerged as an industry-oriented open standard that follows this approach. The space and time decoupling allowed by DDS is very relevant in any dynamic and distributed system, since interacting entities are not forced to know each other and are not forced to be simultaneously present to exchange data. Time decoupling can significantly simplify the management of intermittent data-links, in particular for wireless connectivity between UAS. This model of communication, in turn, questions the locator-based addressing used in IP and instead utilizes a data-centric naming.

In order to clarify and contrast these distinct approaches, it is worth highlighting that in the aerospace industry, it is common practice to distinguish between "system" and "payload" considerations (see above). In principle, command, control (and communications) (C2/C3) link connectivity is limited to system operations, while payload communications is largely out of scope of regulatory frameworks. Practically speaking, especially in light UAV, both types of communications may be overlaid on the same data links.

From this follow legal reliability requirements that apply to systems and C3 links which may make data-centric naming infeasible and making the use of authenticated host-to-host communications a requirement (such as via HIP). For payload communications, named data approaches may be more desirable for their time decoupling properties above.

Both approaches share a need to resolve identifiers to locators. When it comes to C3 link reliability, this translates into an end-point selection problem, as multiple underlying links may be available, but the determination of the "best" link depends on specific radio characteristics [FINKHAUSER21] or even the vehicle's spatial location.

In the case of using IP, mobility of UAVs introduces a significant challenge. Consider the case where a GCS is receiving telemetry information from a specific UAV. Assuming that the UAV moves and changes its point of attachment to the network, it will have to configure a new IP address on its wireless interface. However, this is problematic, as the telemetry information is still being sent by to the previous IP address of the UAV. This simple example illustrates the necessity to deploy mobility management solutions to handle this type of situations.

However, those technologies may not be suitable when the communication includes interconnections of public Internet and private networks (aka private limited domains), or when the movement is so fast that the locator and/or topology update becomes the limitation factor.

Scenarios from research projects such as [COMP4DRONES] and [ADACORSA] regarding connectivity assume worse conditions. Consider an emergency scenario in which 3GPP towers are inoperable. Emergency services need to deploy a mobile ground control station that issues emergency landing overrides to all UAV in the area. UAV must be able to authenticate this mobile GCS to prevent malicious interference with their opreations, but must be able to do so without access to internet-connected authentication databases. HIP provides a means to secure communications to this mobile GCS, with no means for establishing its authority. While such considerations are not directly part of the mechanism by which identifiers may be mapped to locators, they illustrate the need for carrying authenticating and authorizing information within identifiers.

Furthermore, mobility management solutions increase the complexity of the deployment and may impact the performance of data distribution, both in terms of signaling/data overhead and communication path delay. Considering the specific case of multicast data streams, mobility of content producers and consumers is inherently handled by multicast routing protocols, which are able to react to changes of location of mobile nodes by reconstructing the corresponding multicast delivery trees. Nevertheless, this comes with a cost in terms of signaling and data overhead (data may still flow through branches of a multicast delivery tree where there are no receivers while the routing protocol is still converging).

Another alternative is to perform the mobility management of producers and consumers not at the application layer based on IP multicast trees, but on the network layer based on an Information Centric Network approach, which was already mentioned in this section.

Some limited relief may be offered by in-network processing. Sensor data used in autononmous operations becomes ever richer, while available transmission throughput rates do not increase at the same pace. For this reason, the general trend in autonomous vehicles is to move away from transmitting raw sensor data and processing at the ground station. Instead, aggregated Situational Awareness Data is instead transmitted. In networking terms this implies in-network processing, as individual sensor nodes on board a UAV network no longer employ direct communications with a GCS. A similar approach is taken in IoT sensors, where low-powered sensors may send raw data via CoAP [RFC7252] or similar protocols to a processing router, and a UAV collects aggregated data from this router to transmit it to where it may be further processed.

B.4. Communication Across Services

As a communication infrastructure spanning many facets of life, the Internet integrates services and resources from various aspects such as remote collaboration, shopping, content production as well as delivery, education, and many more. Accessing those services and resources directly through URIs has been proposed by methods such as those defined in ICN [RFC7476], where providers of services and resources can advertise those through unified identifiers without additional planning of identifiers and locations for underlying data and their replicas. Users can access required services and resources by virtue of using the URI-based identification, with an ephemeral relationship built between user and provider, while the building of such relationship may be constrained with user- as well as service-specific requirements, such as proximity (finding nearest provider), load (finding fastest provider), and others.

While systems like ICN [JACOBSON09] provide an alternative to the topological addressing of IP, its deployment requires an overlay (over IP) or native deployment (alongside IP), the latter with dedicated gateways needed for translation. Underlay deployments are also envisioned in [RFC8763], where ICN solutions are being used to facilitate communication between IP addressed network endpoints or URI-based service endpoints, still requiring gateway solutions for interconnection with ICN-based networks as well as IP routing based networks (cf., [I-D.irtf-icnrg-5gc-icn][I-D.trossen-icnrg-internet-icn-5glan]).

Although various approaches combining service and location-based addressing have been devised, the key challenge here is to facilitate a "natural", i.e., direct communication, without the need for gateways above the network layer.

Another aspect of communication across services is that of chaining individual services to a larger service. Here, an identifier would be used that serves as a link to next hop destination within the chain of single services, as done in the work on Service Function Chaining (SFC). With this, services are identified at the level of Layer 2/3 ([RFC7665], [RFC8754], [RFC8595]) or at the level of name-based service identifiers like URLs [RFC8677] although the service chain identification is carried as a Network Service header (NSH) [RFC7665], separate to the packet identifiers. The forwarding with the chain of services utilizes individual locator-based IP addressing (for L3 chaining) to communicate the chained operations from one Service Function Forwarder [RFC7665] to another, leading to concerns regarding overhead incurred through the stacking of those chained identifiers in terms of packet overhead and therefore efficiency in handling in the intermediary nodes.

B.5. Communication Traffic Steering

Steering traffic within a communication scenario may involve at least two aspects, namely (i) limiting certain traffic towards a certain set of communication nodes and (ii) restraining the sending of packets towards a given destination (or a chain of destinations) with metrics that would allow the selection among one or more possible destinations.

One possibility for limiting traffic inside limited domains, towards specific objects, e.g., devices, users, or group of them, is subnet partition with techniques such as VLAN [RFC5517], VxLAN [RFC7348], or more evolved solution like TeraStream [TERASTREAM] realizing such partitioning. Such mechanisms usually involve significant configuration, and even small changes in network and user nodes could result in a repartition and possibly additional configuration efforts. Another key aspect is the complete lack of correlation of the topological address and any likely more semantic-rich identification that could be used to make policy decisions regarding traffic steering. Suitably enriching the semantics of the packet address, either that of the sender or receiver, so that such decision could be made while minimizing the involvement of higher layer mechanisms, is a crucial challenge for improving on network operations and speed of such limited domain traffic.

When making decisions to select one out of a set of possible destinations for a packet, IP anycast semantics can be applied albeit being limited to the locator semantic of the IP address itself. Recent work in [WION19] suggests utilizing the notion of IP anycast address to encode a "service identifier", which is dynamically mapped onto network locations where service instances fulfilling the service request may be located. Scenarios where this capability may be utilized are provided in [WION19] and include, but are not limited to, scenarios such as edge-assisted VR/AR, transportation, smart cities, smart homes, smart wearables, and digital twins.

The challenge here lies in the possible encoding of not only the service information itself but the constraint information that helps the selection of the "best" service instance and which is likely a service-specific constraint in relation to the particular scenario. The notion of an address here is a conditional (on those constraints) one where this conditional part is an essential aspect of the forwarding action to be taken. It needs therefore consideration in the definition of what an address is, what is its semantic, and how the address structure ought to look like.

As outlined in the previous sub-section, chaining services are another aspect of steering traffic along a chain of constituent services, where the chain is identified through either a stack of individual identifiers, such as in Segment Routing [RFC8402], or as an identifier that serves as a link to next hop destination within the chain, such as in Service Function Chaining (SFC). The latter can be applied to services identified at the level of Layer 2/3 ([RFC7665], [RFC8754], [RFC8595]) or at the level of name-based service identifiers like URLs [RFC8677]. However, the overhead incurred through the stacking of those chained identifiers is a concern in terms of packet overhead and therefore efficiency in handling in the intermediary nodes.

B.6. Communication with built-in security

Today, strong security in the Internet is usually implemented as a general network service ([KRAHENBUHL21], [RFC6158]). Among the various reasons for such approach is the limited semantic of current IP addresses, which do not allow to natively express security features or trust relationships. In specific contexts strong identification and tracking is necessary for safety and security purposes, like for instance for UAS [RFC9153] or aeronautical telecommunications networks [I-D.haindl-lisp-gb-atn]. This becomes very cumbersome when communication goes beyond limited domains and in the public Internet, where security and trust associated to those identifier may be lost or just impossible to verify.

Efforts like Cryptographically Generated Addresses (CGA) [RFC3972], provide some security features by embedding a truncated public key in the last 57-bit of IPv6 address, thereby greatly enhancing authentication and security within an IP network via asymmetric cryptography and IPsec [RFC4301]. The development of the Host Identity Protocol (HIP) [RFC7401] saw the introduction of cryptographic identifiers for the newly introduced Host Identity (HI) to allow for enhanced accountability, and therefore trust. The use of those HIs, however, is limited by the size of IPv6 128bit addresses.

Through a greater flexibility in addressing, any security-related key, certificate, or identifier could instead be included in a suitable address structure without any information loss (i.e., as-is, without any truncation or operation as such), avoiding therefore compromises such as those in HIP. Instead, CGAs could be created using full length certificates, or being able to support larger HIP addresses in a limited domain that uses it. This could significantly help in constructing a trusted and secure communication at the network layer, leading to connections that could be considered as absolute secure (assuming the cryptography involved is secure). Even more, anti-abuse mechanisms and/or DDoS protection mechanisms like the one under discussion in PEARG ([PEARG]) Research Group may leverage a greater flexibility of the overall Internet addressing, if provided, in order to be more effective.

B.7. Communication protecting user privacy

The last decade has witnessed increasing concerns for user privacy ([RFC7258], [RFC6973]). IP Addresses are particularly exposed because they can easily be associated to end users, allowing fingerprinting and cross-site linking ([BUJLOW17], [MISHRA20]). Indeed, while encryption is widely used to conceal the traffic payload, the IP header remain, and particularly IP addresses, must be transmitted in clear in order to forward packets.

One widely used approach to obfuscate the mapping between end users and IP addresses is the use of temporary addresses [RFC8981]. The idea here is to reduce the time window during which eavesdroppers and information collectors can correlate network activity based on the simple IP address. Ephemeral IP addresses have been in the working for more than 30 years [I-D.irtf-pearg-numeric-ids-history], showing that having a temporal semantic in IP addresses can provide improved privacy protection.

B.8. Communication in Alternative Forwarding Architectures

The performance of communication networks has long been a focus for optimization, due to the immediate impact on cost of ownership for communication service providers. Technologies like MPLS [RFC3031] have been introduced to optimize lower layer communication, e.g., by mapping L3 traffic into aggregated labels of forwarding traffic for the purposes of, e.g., traffic engineering.

Even further, other works have emerged in recent years that have replaced the notion of packets with other concepts for the same purpose of improved traffic engineering and therefore efficiency gains. One such area is that of Software Defined Networks (SDN) [RFC7426], which has highlighted how a majority of Internet traffic is better identified by flows, rather than packets. Based on such observation, alternate forwarding architectures have been devised that are flow-based or path-based. With this approach, all data belonging to the same traffic stream is delivered over the same path, and traffic flows are identified by some connection or path identifier rather than by complete routing information, possibly enabling fast hardware based switching (e.g. [DETNETWG], [PANRG]).

On the one hand, such a communication model may be more suitable for real-time traffic like in the context of Deterministic Networks ([DETNETWG]), where indeed a lot of work has focused on how to "identify" packets belonging to the same DETNET flow in order to jointly manage the forwarding within the desired deterministic boundaries.

On the other hand, it may improve the communication efficiency in constrained wireless environments (cf., Appendix B.1), by reducing the overhead, hence increasing the number of useful bits per second per Hertz.

Also, the delivery of information across similar flows may be combined into a multipoint delivery of a single return flow, e.g., for scenarios of requests for a video chunk from many clients being responded to with a single (multi-destination) flow, as outlined in [I-D.ietf-bier-multicast-http-response] as an example. Another opportunity to improve communication efficiency is being pursued in ongoing IETF/IRTF work to deliver IP- or HTTP-level packets directly over path-based or flow-based transport network solutions, such as in [TROSSEN10], [I-D.ietf-bier-multicast-http-response],[I-D.trossen-icnrg-internet-icn-5glan], and [I-D.irtf-icnrg-5gc-icn], with the capability to bundle unicast forward communication streams flexibly together in return path multipoint relations. Such capability is particularly opportune in scenarios such as chunk-based video retrieval or distributed data storage. However, those solutions currently require gateways to "translate" the flow communication into the packet-level addressing semantic in the peering IP networks. Furthermore, the use of those alternative forwarding mechanisms often require the encapsulation of Internet addressing information, leading to wastage of bandwidth as well as processing resources.

Providing an alternative way of forwarding data has also been the motivation for the efforts created in the European Telecommunication Standards Institute (ETSI), which formed an Industry Specification Group (ISG) named Non-IP Networking (NIN) [ETSI-NIN]. This group sets out to develop and standardize a set of protocols leveraging an alternative forwarding architecture, such as provided by a flow-based switching paradigm. The deployment of such protocols may be seen to form limited domains, still leaving the need to interoperate with the (packet-based forwarding) Internet; a situation possibly enabled through a greater flexibility of the addressing used across Internet-based and alternative limited domains alike.

As an alternative to IP routing, EIBP (Extended Internet Bypass Protocol) [SHENOY21] offers a communications model that can work with IP in parallel and entirely transparent and independent to any operation at network layer. For this, EIBP proposes the use of physical and/or virtual structures in networks and among networks to auto assign routable addresses that capture the relative position of routers in a network or networks in a connected set of networks, which can be used to route the packets between end domains. EIBP operates at Layer 2.5 and provides encapsulation (at source domain), routing, and de-encapsulation (at destination domain) for packets. EIBP can forward any type of packets between domains. A resolver to map the domain ID to EIBP's edge router addresses is required. When queried for a specific domain, the resolver will return the corresponding edge router structured addresses.

EIBP decouples routing operations from end domain operations, offering to serve any domain, without point solutions to specific domains. EIBP also decouples routing IDs or addresses from end device/domain addresses. This allows for accommodation of new and upcoming domains. A domain can extend EIBP's structured addresses into the domain, by joining as a nested domain under one or more edge routers, or by extending the edge router's structure addresses to its devices.

Appendix C. Examples of Internet Addressing Properties Extensions

C.1. Length Extensions

C.1.1. Shorter Address Length Examples

  • Header Compression/Translation: Considering one base station is supposed to serve hundreds of user devices, maximizing the effectiveness for specific spectrum directly improves user quality of experience. To achieve the optimal utilization of the spectrum resource in the wireless area, the RObust Header Compression (ROHC) [RFC5795] mechanism, which has been widely adopted in cellar network like WCDMA, LTE, and 5G, utilizes header compression to shrink existing IPv6 headers onto shorter ones.
  • Similarly, header compression techniques for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPAN) have been around for several years now, constituting a main example of using the notion of a 'shared context' in order to reduce the size of the network layer header ([RFC6282], [RFC7400], [BADENHOP15]). More recently, other compression solutions have been proposed for Low Power Wide Area Networks (LPWAN - [RFC8376]). Among them, the Static Context Header Compression (SCHC - [RFC8724]) generalized the compression mechanism developed by 6lo. Instead of a standard compression behavior implemented in all 6lo nodes, SCHC introduces the notion of rules shared by two nodes. The SCHC compression technique is generic and can be applied to IPv6 and layers above. Regarding the nature of the traffic, IPv6 addresses (source and destination) can be elided, partially sent, or replaced by a small index. Instead of the versatile IP packet, SCHC defines new packet formats dedicated to specific applications. SCHC rules are equivalence functions mapping this format to standard IP packets.

  • Also, constraints coming from either devices or carrier links would lead to mixed scenarios and compound requirements for extraordinary header compression. For native IPv6 communications on DECT ULE and MS/TP Networks [RFC6282], dedicated compression mechanisms are specified in [RFC8105] and [RFC8163], while the transmission of IPv6 packets over NFC and PLC, specifications are being developed in [I-D.ietf-6lo-nfc] and [RFC9354].

  • Separate device from locator identifier: Solutions such as proposed in Expedited Internet Bypass Protocol [SHENOY21] and [RFC9300] can utilize a separation of device from locator, where only the latter is used for routing between the different domains using the same technology, therefore enabling the use of shorter addresses in the (possibly constrained) local environment. Device IDs used within such domains are carried as part of the payload by EIBP and hence can be of shorter size suited to the domain, while, for instance, in LISP a flexible address encoding [RFC8060] allows shorter addresses to be supported in the LISP control plane [RFC9301].

C.1.2. Longer Address Length Examples

  • Split address zone by network realm: Network Address Translation (NAT), which was first laid out in [RFC2663], using private address and a stateful address binding to translate between the realms. As outlined in [RFC2663], basic address translation is usually extended to include port number information in the translation process, supporting bidirectional or simple outbound traffic only. Because the 16-bits port number is used in the address translation, NAT theoretically increase IPv4 address length from 32-bit to 48-bit, i.e., 281 trillion address space.
  • Similarly, EzIP [I-D.chen-ati-adaptive-ipv4-address-space] expects to utilize a reserved address block, i.e., 240/4, and an IPv4 header option to include it. Based on this, it can be regarded as EzIP is carrying a hierarchical address with two parts, where each part is a partial 32-bit IPv4 address. The first part is a public address residing in the "address field" of the header from globally routable IPv4 pool [IPv4pool], i.e., ca. 3.84 billion address space. The second part is the reserved address residing in "option field" and belongs to the 240/4 prefix, i.e., ca. 2^28=268 million. Based on that, each EzIP deployment is tethered on the existing Internet via one single IPv4 address, and EzIP then have 3.84B * 268M address, ca. 1,000,000 trillion. Collectively, the 240/4 can also be used as end point identifier and form an overlay network providing services parallel to the current Internet, yet independent of the latter in other aspects.

  • Compared to NAT, EzIP is able to establish a communication session from either side of it, hence being completely transparent, and facilitating a full end-to-end networking configuration.

C.2. Identity Extensions

C.2.1. Anonymous Address Identity Examples

  • Traffic Proxy: Although not initially designed as a traffic proxy approach, a Virtual Private Network (VPN [KHANVILKAR04]) is widely utilized for packets origin hiding as a traffic detouring methodology. As it evolved, VPN derivatives like WireGuard [DONENFELD17] have become a mainstream instance for user privacy and security enhancement.
  • With such methodology in mind, onion routing [GOLDSCHLAG99], instantiated in the Tor Project [TOR], achieves high anonymity through traffic hand over via intermediates, before reaching the destination. Since the architecture of Tor requires at least three proxies, none of them is aware of the entire route. Given that the proxies themselves can be deployed all over cyberspace, trust is not the prerequisite if proxies are randomly selected.

  • In addition, dedicated protocols are also expected to be customized for privacy improvement via traffic proxy. For example, Oblivious DNS over HTTPS (ODoH [RFC9230]) use a third-party proxy to obscure identifications of user source addresses during DNS over HTTPS (DoH [RFC8484]) resolution. Similarly, Oblivious HTTP (OHTTP [I-D.thomson-http-oblivious]) involve proxy alike in the HTTP environment.

  • Source Address Rollover: As for source address rollover, it has been standardized that IP addresses for Internet users should be dynamic and temporary every time they are being generated [RFC8981]. This benefits from the available address space in the case of IPv6, through which address generation or assignment should be unpredictable and stochastic for outside observers.
  • More radically, [I-D.gont-v6ops-ipv6-addressing-considerations] advocates an 'ephemeral address', changing over time, for each process. Through this, correlating user behaviors conducted by different identifiers (i.e., source address) becomes much harder, if not impossible, if based on the IP packet header alone.

  • Private Addresses: The use and assignment of private addresses for IPv4 is laid out in [RFC1918], while unique local addresses (ULAs) in IPv6 [RFC4193] take over the role of private address spaces in IPv4.
  • Network Address Translation: Given address translation can be performed several times in cascade, NATs may exist as part of existing customer premise equipment (CPE), such as a cable or an Ethernet router, with private wired/wireless connectivity, or may be provided in a carrier environment to further translate ISP-internal private addresses to a pool of (assigned) public IP addresses. The latter is often dynamically assigned to CPEs during its bootstrapping.
  • Separate device from locator identifier: EIBP [SHENOY21] utilizes a structured approach to addressing. It separates the routing ID from the device ID, where only the former is used for routing. As such, the device IDs can be encrypted, protecting the end device identity. Similarly, LISP uses separate namespaces for routing and identification allowing to 'hide' identifiers in encrypted LISP packets that expose only known routing information [RFC8061].

C.2.2. Authenticated Address Identity Examples

  • Self-certified Addresses: As an example of this methodology serves [RFC3972], defining IPv6 cryptographically Generated Addresses (CGA). A Cryptographically Generated Address is formed by replacing the least-significant 64 bits of an IPv6 address with the cryptographic hash of the public key of the address owner. Packets are then signed with the private key of the sender. Packets can be authenticate by the receiver by using the public key of the sender and the address of the sender. The original specifications have been already amended (cf., [RFC4581] and [RFC4982]) in order to support multiple (stronger) cryptographic algorithms.
  • Collision-resistant addresses: In order to provide a mechanism for IP mobility considerations, [RFC7343] defines Overlay Routable Cryptographic Hash Identifiers (ORCHIDv2). ORCHIDs use a determinstic scheme for generating statistically unique addresses by concatenating a designated IPv6 prefix, a hash function identifier, and a truncated hash. The hash input is a unique, statically assigned context identifier concatenated with random data. A variation of this scheme is proposed to solve requirements of [RFC9153] in identification of unmanned aerial vehicles using Drone Remote Identification Protocol Entity Tags (DRIP Entity Tag; DET) [RFC9374]. This variation proposes a distinct IPv6 prefix and new hash functions, but the major change is to further truncate the hash, and use the freed bits for a two-level registration authority hierarchy. The hierarchy is intended for delegation both when registering and validating DETs globally.
  • Third party granted addresses: [RFC3118] defines a DHCP option through which authorization tickets can be generated and newly attached hosts with proper authorization can be automatically configured from an authenticated DHCP server. Solutions exist where separate servers are used for user authentication like [KOMORI02] and [RFC4014]. The former proposing to enhance the DHCP system using registered user login and password before actually providing an IP address lease and recording the MAC address of the device the user used to sign-in. The latter, couples the RADIUS authentication protocol ([RFC2865]) with DHCP, basically piggybacking RADIUS attributes in a DHCP sub-option, with the DHCP server contacting the RADIUS server to authenticate the user.

C.3. Semantic Extensions

C.3.1. Extended Address Semantics Examples

  • Semantic prefixes: Newer approaches to IP anycast suggest the use of service identification in combination with a binding IP address model [WION19] as a way to allow for metric-based traffic steering decisions; approaches for Service Function Chaining (SFC) [RFC7665] utilize the Network Service Header (NSH) information and packet classification to determine the destination of the next service.
  • Another example of the usage of different packet header extensions based on IP addressing is Segment Routing. In this case, the source chooses a path and encodes it in the packet header as an ordered list of segments. Segments are encoded using new Routing Extensions Header type, the Segment Routing Header (SRH), which contains the Segment List, similar to what is already specified in [RFC8200], i.e., a list of segment ID (SID) that dictate the path to follow in the network. Such segment IDs are coded as 128 bit IPv6 addresses [RFC8986].

  • Approaches such as [CAROFIGLIO19] utilize semantic prefixing to allow for ICN forwarding behavior within an IPv6 network. In this case, an HICN name is the hierarchical concatenation of a name prefix and a name suffix, in which the name prefix is encoded as an IPv6 128 bits word and carried in IPv6 header fields, while the name suffix is encoded in transport headers fields such as TCP. However, it is a challenge to determine which IPv6 prefixes should be used as name prefixes. In order to know which IPv6 packets should be interpreted based on an ICN semantic, it is desirable to be able to recognize that an IPv6 prefix is a name prefix, e.g. to define a specific address family (AF_HICN, b0001::/16). This establishment of a specific address family allows the management and control plane to locally configure HICN prefixes and announce them to neighbors for interconnection.

  • Separate device from locator identifier: EIBP [SHENOY21] separates the routing locator from the device identifier, relaxing therefore any semantic constraints on the device identifier. Similarly, LISP uses a flexible encoding named LISP Canonical Address Format (LCAF [RFC8061]), which allows to associate to routing locators any possible form (and length) of identifier. ILNP [RFC6740] introduces as well a different semantic of IP addresses, while aligning to the IPv6 address format (128 bits). Basically, ILNP introduces a sharper logical separation between the 64 most significant bits and the 64 least significant bits of an IPv6 address. The former being a global locator, while the latter being an identifier that can have different semantics (rather than just being an interface identifier).
  • Structured addressing: Network topology captures the physical connectivity among devices in the network. There is a structure associated with the topology. Examples are the core-distribution-access router structure commonly used in enterprise networks and clos topologies that are used to provide multiple connections between Top of Rack (ToR) devices and multiple layers of spine devices. Internet service providers use a tier structure that defines their business relationships. A clear structure of connected networks can be noticed in the Internet. EIBP [SHENOY21] proposes to leverage the physical structure (or a virtual structure overlaid on the physical structure) to auto assign addresses to routers in a network or networks in an internetwork to capture their relative position in the physical/virtual topology. EIBP proposes to administratively identify routers/networks with a tier value based on the structure.
  • Localized forwarding semantics: Approaches such as those outlined in [REED16] suggest using a novel forwarding semantic based on path information carried in the packet itself, said path information consists in a fixed size bit-field (see [REED16] for more information on how to represent the path information in said bit-field). In order to utilize existing, e.g., SDN-based, forwarding switches, the direct use of the IPv6 source/destination address is suggested for building appropriate match-action rules (over the suitable binary information representing the local output ports), while preserving the original IPv6 information in the encapsulated packet. As mentioned above, such use of the existing IPv6 address fields limits the size of the network to a maximum of 256 bits (therefore paths in the network over which such packets can be forwarded). [I-D.trossen-icnrg-internet-icn-5glan], however, goes a step further by suggesting to use the local forwarding as direct network layer mechanism, removing the IP packet and only leaving the transport/application layer, with the path identifier constituting the network-level identifier albeit limited by using the existing IP header for backward compatibility reasons (the next section outlines the removal of this limitation).

C.3.2. Existing or Extended Header Semantics Examples

  • In-Header extensions: In order to allow additional semantic with respect to the pure Internet addressing, the original design of IPv4 included the field 'Type of Service' [RFC2474], while IPv6 introduced the 'Flow label' and the 'Traffic Class' [RFC8200] fields. In a certain way, those fields can be considered 'semantic extensions' of IP addresses, and they are 'in-header' because natively present in the IP header (differently from options and extension headers). However, they proved not to be sufficient. Very often a variety of network operations are performed on the well-known 5-tuple (source and destination addresses; source and destination port number; and protocol number). In some contexts all of the above-mentioned fields are used in order to have a very fine grained solution ([RFC8939]).
  • Headers option extensions: Header options have been largely under-exploited in IPv4. However, the introduction of the more efficient extension header model in IPv6 along with technology progress made the use of header extensions more widespread in IPv6. Segment Routing re-introduced the possibility to add path semantic to the packet by encoding a loosely defined source routing ([RFC8402]). Similarly, in the aim to overcome the inherent shortcoming of the multi-homing in the IP context, SHIM6 ([RFC5533]) also proposed the use of an extension header able to carry multi-homing information which cannot be accommodated natively in the IPv6 header.
  • To serve a moving endpoint, mechanisms like Mobile IPv6 [RFC6275] are used for maintaining connection continuity by a dedicated IPv6 extension header. In such case, the IP address of the home agent in Mobile IPv6 is basically an identification of the on-going communication. In order to go beyond the interface identification model of IP, the Host Identity Protocol (HIP) tries to introduce an identification layer to provide (as the name says) host identification. The architecture here relies on the use of another type of extension header [RFC7401].

  • Re-encapsulation extension: Differently from the previous approach, re-encapsulation prepends complete new IP headers to the original packet introducing a completely custom shim header between the outer and inner header. This is the case for LISP, adding a LISP specific header right after an IP+UDP header ([RFC9300]). A similar design is used by VxLAN ([RFC7348]) and GENEVE ([RFC8926]), even if they are designed for a data center context. IP packets can also be wrapped with headers using more generic and semantically rich names, for instance with ICN [I-D.trossen-icnrg-internet-icn-5glan].
  • Structured addressing: Solutions such as those described in the previous sub-section, e.g., EIBP [SHENOY21], can provide structured addresses that are not limited to the IPv6 address length but instead carry the information in an extension header to remove such limitation.
  • Also, Information-Centric Networking (ICN) naming approaches usually introduce structures in the (information) names without limiting themselves to the IP address length; more so, ICN proposes its own header format and therefore radically breaks with not only IP addressing semantic but the format of the packet header overall. For this, approaches such as those described in [RFC8609] define a TLV-based binary application component structure that is carried as a 'name' part of the CCN messages. Such a name is a hierarchical structure for identifying and locating a data object, which contains a sequence of name components. Names are coded based on 2-level nested Type-Length-Value (TLV) encodings, where the name-type field in the outer TLV indicates this is a name, while the inner TLVs are name components including a generic name component, an implicit SHA-256 digest component and a SHA-256 digest of Interest parameters. For textual representation, URIs are normally used to represent names, as defined in [RFC3986].

  • In geographic addressing, position based routing protocols use the geographic location of nodes as their addresses, and packets are forwarded when possible in a greedy manner towards the destination. For this purpose, the packet header includes a field coding the geographic coordinates (x, y, z) of the destination node, as defined in [RFC2009]. Some proposals also rely on extra fields in the packet header to code the distance towards the destination, in which case only the geographic coordinates of neighbors are exchanged. This way the location of the destination is protected even if routing packets are eavesdropped.

  • Localized forwarding semantics: Unlike the original suggestion in [REED16] to use existing SDN switches, the proliferation of P4 [BOSSHART14] opens up the possibility to utilize a locally limited address semantic, e.g., expressed through the path identifier, as an entirely new header (including its new address) with an encapsulation of the IP packet for E2E delivery (including further delivery outside the localized forwarding network) or positioning the limited address semantic directly as the network address semantic for the packet, i.e., removing any IP packet encapsulation from the forwarded packet, as done in [I-D.trossen-icnrg-internet-icn-5glan]. Removing the IPv6 address size limitation by not utilizing the existing IP header for the forwarding decision also allows for extensible length approaches for building the path identifier with the potential for increasing the supported network size. On the downside, this approach requires to encapsulate the original IP packet header for communication beyond the local domain in which the new header is being used, such as discussed in the previous point above on 're-encapsulation extension'.


Dirk Trossen
Huawei Technologies Duesseldorf GmbH
Riesstr. 25C
80992 Munich
Paulo Mendes
Willy-Messerschmitt Strasse 1
81663 Munich
Nirmala Shenoy
Rochester Institute of Technology
New-York, 14623
United States of America
Laurent Toutain
2 rue de la Chataigneraie
CS 17607
35576 Cesson-Sevigne Cedex
Abraham Y. Chen
Avinta Communications, Inc.
142 N. Milpitas Blvd.
Milpitas, CA, 95035-4401
United States of America
Dino Farinacci
United States of America
Jens Finkhaeuser
AnyWi Technologies B.V.
3e Binnenvestgracht 23H
2312 NR Leiden
Peng Liu
China Mobile
32 Xuanwumen West Ave
Xicheng, Beijing
P.R. China
Yihao Jia
Donald E. Eastlake 3rd
Futurewei Technologies
2386 Panoramic Circle
Apopka, FL, 32703
United States of America

Author's Address

Luigi Iannone (editor)
Huawei Technologies France S.A.S.U.
18, Quai du Point du Jour
92100 Boulogne-Billancourt