< draft-king-irtf-challenges-in-routing-07.txt   draft-king-irtf-challenges-in-routing-08.txt >
IRTF D. King RTGWG D. King
Internet-Draft Lancaster University Internet-Draft Lancaster University
Intended status: Informational A. Farrel Intended status: Informational A. Farrel
Expires: 26 July 2022 Old Dog Consulting Expires: 27 October 2022 Old Dog Consulting
C. Jacquenet C. Jacquenet
Orange Orange
22 January 2022 25 April 2022
Challenges for the Internet Routing Infrastructure Introduced by Challenges for the Internet Routing Systems Introduced by Semantic
Semantic Routing Routing
draft-king-irtf-challenges-in-routing-07 draft-king-irtf-challenges-in-routing-08
Abstract Abstract
Historically, the meaning of an IP address has been to identify an Historically, the meaning of an IP address has been to identify an
interface on a network device. Routing protocols were developed interface on a network device. Routing protocols were developed
based on the assumption that a destination address had this semantic. based on the assumption that a destination address had this semantic.
Over time, routing decisions were enhanced to route packets according Over time, routing decisions have been enhanced to determine paths on
to additional information carried within the packets and dependent on which packets could be forwarded according to additional information
carried principally within the packet headers, and dependent on
policy coded in, configured at, or signaled to the routers. policy coded in, configured at, or signaled to the routers.
Many proposals have been made to add semantics to IP packets by Many proposals have been made to add semantics to IP packets by
placing additional information into existing fields, by adding placing additional information into existing fields, by adding
semantics to IP addresses, or by adding fields to the packets. The semantics to IP addresses, or by adding fields to the packets. The
intent is to facilitate routing decisions based on these additional intent is always to facilitate routing decisions based on these
semantics in order to provide differentiated paths for different additional semantics in order to provide differentiated paths to
packet flows distinct from shortest path first or path vector enable forwarding of different packet flows on paths that may be
distinct from those derived by shortest path first or path vector
routing. We call this approach "Semantic Routing". routing. We call this approach "Semantic Routing".
This document describes the challenges to the existing routing system This document describes the challenges to the existing routing system
that are introduced by Semantic Routing. It then summarizes the that are introduced by Semantic Routing. It then summarizes the
opportunities for research into new or modified routing protocols to opportunities for research into new or modified routing and
make use of additional semantics. forwarding approaches that make use of additional semantics.
This document is presented as a study to support further research This document is presented as a study to support further research
into clarifying and understanding the issues. It does not pass into clarifying and understanding the issues. It does not pass
comment on the advisability or practicality of any of the proposals comment on the advisability or practicality of any of the proposals
and does not define any technical solutions. and does not define any technical solutions.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
skipping to change at page 2, line 15 skipping to change at page 2, line 15
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on 26 July 2022. This Internet-Draft will expire on 27 October 2022.
Copyright Notice Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/ Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document. license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
skipping to change at page 2, line 39 skipping to change at page 2, line 39
provided without warranty as described in the Revised BSD License. provided without warranty as described in the Revised BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Current Challenges to IP Routing . . . . . . . . . . . . . . 4 2. Current Challenges to IP Routing . . . . . . . . . . . . . . 4
3. What is Semantic Routing? . . . . . . . . . . . . . . . . . . 7 3. What is Semantic Routing? . . . . . . . . . . . . . . . . . . 7
3.1. Architectural Considerations . . . . . . . . . . . . . . 9 3.1. Architectural Considerations . . . . . . . . . . . . . . 9
4. Challenges for Internet Routing Research . . . . . . . . . . 10 4. Challenges for Internet Routing Research . . . . . . . . . . 10
4.1. Research Principles . . . . . . . . . . . . . . . . . . . 10 4.1. Research Principles . . . . . . . . . . . . . . . . . . . 10
4.2. Routing Research Questions to be Addressed . . . . . . . 10 4.2. Routing Research Questions to be Addressed . . . . . . . 11
5. Security and Privacy Considerations . . . . . . . . . . . . . 15 5. Security and Privacy Considerations . . . . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16
9. Informative References . . . . . . . . . . . . . . . . . . . 16 9. Informative References . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
Historically, the meaning of an IP address has been to identify an Historically, the meaning of an IP address has been to identify an
interface on a network device. Routing protocols were developed to interface on a network device. Routing protocols were to compute,
compute, establish, and maintain paths through networks toward establish, and maintain paths through networks toward destination
destination prefixes until IP packets eventually reach their prefixes until IP packets eventually reach their destination, and
destination. Anycast and multicast addresses were also defined, and were based on the assumption that a destination address had this
semantic. Anycast and multicast addresses were also defined, and
those address semantics sometimes required variations to the routing those address semantics sometimes required variations to the routing
protocols or even encouraged the development of new protocols. protocols or even encouraged the development of new protocols.
Over time, the mechanisms that enabled routing decisions were Over time, the mechanisms that enabled routing decisions were
enhanced to forward packets according to additional information enhanced to determine paths on which packets could be forwarded
carried within the packets or within 'shim' headers, and dependent on according to additional information carried principally within the
policy coded in, configured at, or signaled to the routers. Perhaps packets headers or within 'shim' headers, and dependent on policy
one of the most iconic examples is Equal-Cost Multipath (ECMP) where coded in, configured at, or signaled to the routers. Perhaps one of
a router makes a choice for forwarding packets over a number of the most iconic examples is Equal-Cost Multipath (ECMP) where a
router makes a choice about how to forward a packet over a number of
parallel links or paths based on the values of a set of fields in the parallel links or paths based on the values of a set of fields in the
packet header. packet header.
Many proposals have been made to add semantics to IP packets by Many proposals have been made to add semantics to IP packets by
placing additional information into existing fields, by adding placing additional information into existing fields, by adding
semantics to IP addresses, or by adding fields to the packets. The semantics to IP addresses, or by adding fields to the packets. The
intent is to improve route computation and forwarding choices based intent is always to facilitate routing decisions based on these
on these additional semantics which may lead to the establishment of additional semantics in order to provide differentiated paths to
distinct paths for different packet flows: for example, shortest path enable forwarding of different packet flows on paths that may be
first or path vector routing. We call this approach "Semantic distinct from those derived by shortest path first or path vector
Routing" [I-D.farrel-irtf-introduction-to-semantic-routing]. routing. We call this approach "Semantic Routing"
[I-D.farrel-irtf-introduction-to-semantic-routing].
There are many approaches to adding semantics to packet headers. There are many approaches to adding semantics to packet headers: the
These range from assigning an address prefix to have a special additional information may be derived from the destination addresses,
purpose and meaning (such as is done for multicast addressing) from other fields in the packet header, or the packet itself.
through allowing the owner of a prefix to use the low-order bits of Mechanisms for using the destination address range from assigning an
an address for specific purposes (e.g., to provide an indication of address prefix to have a special purpose and meaning (such as is done
the nature of the service that is associated with these packets). for multicast addressing) through allowing the owner of a prefix to
Some proposals suggest variable address lengths, others offer new use the low-order bits of an address for specific purposes (e.g., to
hierarchical address formats, and some introduce a structure to provide an indication of the nature of the service that is associated
addresses so that they can carry additional information in a common with these packets). Some proposals suggest variable address
way. Other approaches perform routing decisions on fields in the lengths, others offer new hierarchical address formats, and some
packet header (such as the IPv6 Flow Label, or the Traffic Class introduce a structure to addresses so that they can carry additional
field), overload packet fields, or add new information to packet information in a common way. Alternatively, forwarding decisions can
headers. be performed based on fields in the packet header (such as the IPv6
Flow Label, or the Traffic Class field), overloading of existing
packet fields, or new fields added to the packet headers.
A survey of ways in which routing decisions have been made based on A survey of ways in which routing and forwarding decisions have been
additional information carried in packets can be found in made based on additional information carried in packets can be found
[I-D.king-irtf-semantic-routing-survey]. in [I-D.king-irtf-semantic-routing-survey].
Some Semantic Routing proposals are intended to be deployed in Some Semantic Routing proposals are intended to be deployed in
administratively scoped IP domains whose network components (routers, administratively scoped IP domains whose network components (routers,
switches, etc.) are operated by a single administrative entity switches, etc.) are operated by a single administrative entity
(sometimes referred to as 'limited domains' [RFC8799]), while other (sometimes referred to as 'limited domains' [RFC8799]), while other
proposals are intended for use across the Internet. The impact the proposals are intended for use across the Internet. The impact the
proposals have on routing systems may require clean-slate solutions, proposals have on routing systems may require clean-slate solutions,
hybrid solutions, extensions to existing routing protocols, or hybrid solutions, extensions to existing routing protocols, or
potentially no changes at all. potentially no changes at all.
This document describes some of the key challenges to routing that This document describes some of the key challenges to the routing
are present in today's IP networks. It then defines the concept of system that are already present in today's IP networks. It then
"Semantic Routing" and presents some of the challenges to the briefly outlines the concept of "Semantic Routing" with reference to
existing routing system that Semantic Routing may present. Finally, [I-D.farrel-irtf-introduction-to-semantic-routing] and presents some
this document presents a list of related research questions that of the additional challenges to the existing routing system that
offer opportunities for future research into new or modified routing Semantic Routing may introduce. Finally, this document presents a
protocols that make use of Semantic Routing. list of research questions that offer opportunities for future
research into new or modified routing protocols and forwarding
systems that make use of Semantic Routing.
In this document, the focus is on routing and forwarding at the IP In this document, the focus is on routing and forwarding at the IP
layer. A variety of overlay mechanisms exist to perform service or layer. A variety of overlay mechanisms exists to perform service or
path routing at higher layers, and those approaches may be based on path routing at higher layers, and those approaches may be based on
similar extensions to packet semantics, but that is out of scope for similar extensions to packet semantics, but that is out of scope for
this document. Similarly, it is possible that Semantic Routing can this document. Similarly, it is possible that Semantic Routing can
be applied in a number of underlay network technologies, and that, be applied in a number of underlay network technologies, and that,
too, is out of scope for this document. too, is out of scope for this document.
This document is presented as a study to support further research This document is presented as a study to support further research
into clarifying and understanding the issues. It does not pass into clarifying and understanding the issues. It does not pass
comment on the advisability or practicality of any of the proposals comment on the advisability or practicality of any of the proposals
and does not define any technical solutions. and does not define any technical solutions.
2. Current Challenges to IP Routing 2. Current Challenges to IP Routing
Today's IP routing faces several significant challenges which are a Today's IP routing faces several significant challenges which are a
consequence of architectural design decisions and the continued consequence of architectural design decisions and the continued
exponential traffic growth. These challenges include mobility, exponential growth in traffic. These challenges include mobility,
multihoming, programmable paths, scalability, and security, and were multihoming, programmable paths, scalability, and security, and were
not the focus of the original design of the Internet. Nevertheless, not the focus of the original design of the Internet. Nevertheless,
IP networks have, in general, coped well in an incremental manner IP networks have, in general, coped well in an incremental manner
whenever a new challenge has arisen. The following list is presented whenever a new challenge has arisen. The following list is presented
to give context to the continuing requirements that routing protocols to give context to the continuing requirements that routing protocols
must meet as new semantics are applied to the routing process. must meet as new semantics are applied to the routing process.
* Mobility - Mobility introduces several challenges, including * Mobility - Mobility introduces several challenges, including
maintaining a relationship between a sender and a receiver in maintaining a relationship between a sender and a receiver in
cases where the sender or receiver changes their point of network cases where the sender or receiver changes their point of network
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table sizes also grow, even more so when prefixes are not always table sizes also grow, even more so when prefixes are not always
amenable to aggregation. This problem is exacerbated by some amenable to aggregation. This problem is exacerbated by some
services (such as those supported by the IoT where several services (such as those supported by the IoT where several
thousands of objects/sensors may be networked), where, as more thousands of objects/sensors may be networked), where, as more
devices are added to the network, the size of the routing table devices are added to the network, the size of the routing table
may affect the operation of certain routing protocols. It may be may affect the operation of certain routing protocols. It may be
noted that scaling issues are also exacerbated by multihoming noted that scaling issues are also exacerbated by multihoming
practices if a host that is multihomed is allocated a different practices if a host that is multihomed is allocated a different
address for each point of attachment. address for each point of attachment.
* Manageability, Maintainability, and Extensibility - Operational
manageability is a key requirement for network technologies:
network operators must be able to determine the status of their
network and understand the causes of any disruptions or problems.
Further, it must be possible to maintain the networks and the
technologies running in them without disrupting the services being
delivered by the networks. Additionally, the network technologies
developed and deployed need to be extensible so that new features
can be added and new services supported without the need to invent
whole new technologies.
* Security - Issues of security and privacy have been largely * Security - Issues of security and privacy have been largely
overlooked by the routing systems. However, there is increasing overlooked by the routing systems. However, there is increasing
concern that attacks on routing systems can not only be disruptive concern that attacks on routing systems can not only be disruptive
(for example, causing traffic to be dropped), but may cause (for example, causing traffic to be dropped), but may cause
traffic to be redirected to inspection points that can breach the traffic to be redirected to inspection points that can breach the
security or privacy of the payloads. security or privacy of the payloads.
Some of the challenges outlined here were previously considered Some of the challenges outlined here were previously considered
within the IETF by the IAB's "Routing and Addressing Workshop" held within the IETF by the IAB's "Routing and Addressing Workshop" held
in Amsterdam, The Netherlands on October 18-19, 2006 [RFC4984]. in Amsterdam, The Netherlands on October 18-19, 2006 [RFC4984].
Several architectures and protocols have since been developed and Several architectures and protocols have since been developed and
worked on within and outside the IETF, and these are examined in worked on within and outside the IETF, and these are examined in
[I-D.king-irtf-semantic-routing-survey]. [I-D.king-irtf-semantic-routing-survey].
3. What is Semantic Routing? 3. What is Semantic Routing?
Semantic Routing is the term applied to routing in an IP network that Semantic Routing is the term applied to routing in an IP network that
relies upon additional information to feed the route computation relies upon additional information to feed the route computation
process and route selection decisions. Such information may be process, to enhance route selection decisions, and to direct the
present in the packet and configured or programmed into the routers forwarding process. In addition to the routable part of the
in addition to the routable part of the destination IP address (the destination IP address (the prefix), such information may be present
prefix). Semantic Routing includes mechanisms such as "Preferential in other fields in the packet (chiefly the packet header) and
Routing", "Policy-based Routing", and "Flow steering". configured or programmed into the routers/forwarders. Semantic
Routing includes mechanisms such as "Preferential Routing", "Policy-
based Routing", and "Flow steering".
In semantic routing, a packet forwarding engine may examine a variety In Semantic Routing, a packet forwarding engine may examine a variety
of fields in a packet and match them against forwarding instructions. of fields in a packet and match them against forwarding instructions.
Those forwarding instructions may be installed by routing protocols, Those forwarding instructions may be installed by routing protocols,
configured through management protocols or a software defined configured through management protocols or a software defined
networking (SDN) controller, or derived by a software component on networking (SDN) controller, or derived by a software component on
the router that considers network conditions and traffic loads. The the router that considers network conditions and traffic loads. The
packet fields concerned may be the fields of an IP header, those same packet fields concerned may be the fields of an IP header, those same
fields but with additional semantics, elements of the packet payload, fields but with additional semantics, elements of the packet payload,
or new fields defined for inclusion in the packet header. In the or new fields defined for inclusion in the packet header or as a
case of additional semantics included in existing packet header "shim" between the header and payload. In the case of additional
fields, the approach implies some "overloading" of those fields to semantics included in existing packet header fields, the approach
include meaning beyond the original definition. In all cases, a implies some "overloading" of those fields to include meaning beyond
well-known definition of the encoding of the additional information the original definition. In all cases, a well-known definition of
is required to enable consistent interpretation within the network. the encoding of the additional information is required to enable
consistent interpretation within the network.
A more detailed description of semantic routing can be found in A more detailed description of Semantic routing can be found in
[I-D.farrel-irtf-introduction-to-semantic-routing] and a survey of [I-D.farrel-irtf-introduction-to-semantic-routing] and a survey of
semantic routing proposals and research projects can be found in Semantic Routing proposals and research projects can be found in
[I-D.king-irtf-semantic-routing-survey]. [I-D.king-irtf-semantic-routing-survey].
Many technical challenges exist for semantic routing in IP networks Many technical challenges exist for Semantic Routing in IP networks
depending on which approach is taken. These include (but are not depending on which approach is taken. These challenges include (but
limited to): are not limited to):
* The continual growth of routing tables. * The continual growth of routing tables.
* Convergence times for large networks. * Convergence times for large networks.
* Granularity of routing decisions. * Granularity of routing decisions.
* Address consumption caused by lower address utility rate. The * Address consumption caused by lower address utility rate. The
wastage mainly comes from aligning finite allocation for semantic wastage mainly comes from aligning finite allocation for semantic
address blocks. address blocks.
* Encoding too many semantics into prefixes will require evaluation * Encoding too many semantics into prefixes will require evaluation
of which to prioritize. of which to prioritize.
* Risk of privacy/information leakage. * Risk of privacy/information leakage.
* Lack of visibility of the semantic routing information when end- * Lack of visibility of the Semantic Routing information when end-
to-end or edge-to-edge encryption is used. to-end or edge-to-edge encryption is used.
* Burdening the user, application, or prefix assignment node. * Burdening the user, application, or prefix assignment node.
* Source address spoofing prevention mechanisms are required. * Source address spoofing prevention mechanisms are required.
* Overloading of routing protocols causing stability and scaling * Overloading of routing protocols causing stability and scaling
problems. problems.
* Depending on encoding mechanisms, there may be challenges for data * Depending on encoding mechanisms, there may be challenges for data
planes to scale the processes of finding, reading, and looking up planes to scale the processes of finding, reading, and looking up
semantic data in order to forward packets at line speed. semantic data in order to forward packets at line speed.
* Backwards compatibility with existing IP networking and routing * Backwards compatibility with existing IP networking and routing
protocols. protocols.
* Extensibility to support additional functions in the future.
* Manageability and network diagnostics to be able to determine how
the network is functioning and to isolate the causes of any
problems.
3.1. Architectural Considerations 3.1. Architectural Considerations
Semantic data may be taken into account to integrate with existing Semantic data may be taken into account to integrate with existing
routing architectures. An overlay can be built such that semantic routing architectures. An overlay can be built such that Semantic
routing is used to forward traffic between nodes in the overlay, but Routing is used to forward traffic between nodes in the overlay, but
regular IP is used in the underlay. The application of semantics may regular IP is used in the underlay. The application of semantics may
also be constrained to within a limited domain. In some cases, such also be constrained to within a limited domain. In some cases, such
a domain will use IP, but be disconnected from the Internet. In a domain will use IP, but be disconnected from the Internet. In
other cases, traffic from within the domain is exchanged with other other cases, traffic from within the domain is exchanged with other
domains that are connected together across an IP network using domains that are connected together across an IP network using
tunnels or via application gateways. And in still another case tunnels or via application gateways. And in still another case
traffic from the domain is forwarded across the Internet to other traffic from the domain is forwarded across the Internet to other
nodes and this requires backward-compatible routing approaches. nodes and this requires backward-compatible routing approaches.
Isolated Domains: Some IP network domains are entirely isolated from Isolated Domains: Some IP network domains are entirely isolated from
the Internet and other IP networks. In these cases, packets the Internet and other IP networks. In these cases, packets
cannot "escape" from the isolated domain into external networks cannot "escape" from the isolated domain into external networks
and so the semantic routing schemes applied within the domain can and so the Semantic Routing schemes applied within the domain can
have no detrimental effects on external domains. Thus, the have no detrimental effects on external domains. Thus, the
challenges are limited to enabling the desired function within the challenges are limited to enabling the desired function within the
domain. domain.
Bridged Domains: In some deployments, it will be desirable to Bridged Domains: In some deployments, it will be desirable to
connect together multiple isolated domains to build a larger connect together multiple isolated domains to build a larger
network. These domains may be connected (or bridged) over an IP network. These domains may be connected (or bridged) over an IP
network or even over the Internet, possibly using tunnels. An network or even over the Internet, possibly using tunnels. An
alternative to tunneling is achieved using gateway functionality alternative to tunneling is achieved using gateway functionality
where packets from a domain are mapped at the domain boundary to where packets from a domain are mapped at the domain boundary to
produce regular IP packets that are sent across the IP network. produce regular IP packets that are sent across the IP network.
Semantic Prefix Domains: A semantic prefix domain is a portion of Semantic Prefix Domains: A semantic prefix domain is a portion of
the Internet over which a consistent set of semantic-based the Internet over which a consistent set of semantic-based
policies are administered in a coordinated fashion. This is policies are administered in a coordinated fashion. This is
achieved by assigning a routable address prefix (or a set of achieved by assigning a routable address prefix (or a set of
prefixes) for use with semantic routing so that packets may be prefixes) for use with Semantic Routing so that packets may be
forwarded through the regular IP network (or the Internet). Once forwarded through the regular IP network (or the Internet). Once
delivered to the semantic prefix domain, a packet can be subjected delivered to the semantic prefix domain, a packet can be subjected
to whatever semantic routing is enabled in the domain. to whatever Semantic Routing is enabled in the domain.
Further discussion of architectures for semantic routing can be found Further discussion of architectures for Semantic Routing can be found
in [I-D.farrel-irtf-introduction-to-semantic-routing]. in [I-D.farrel-irtf-introduction-to-semantic-routing].
4. Challenges for Internet Routing Research 4. Challenges for Internet Routing Research
It may not be possible to embrace all emerging scenarios with a It may not be possible to embrace all emerging scenarios with a
single approach or solution. Requirements such as 5G mobility, near- single approach or solution. Requirements such as 5G mobility, near-
space-networking, and networking for outer-space (inter-planetary space-networking, and networking for outer-space (inter-planetary
networking), may need to be handled using different network networking), may need to be handled using different network
technologies. Improving IP network capabilities and capacity to technologies. Improving IP network capabilities and capacity to
scale, and address a set of growing requirements presents significant scale, and address a set of growing requirements presents significant
research challenges, and will require contributions from the research challenges, and will require contributions from the
networking research community. Solutions need to be both networking research community. Solutions need to be both
economically feasible and have the support of the networking economically feasible and have the support of the networking
equipment vendors as well as the network operators. equipment vendors as well as the network operators.
4.1. Research Principles 4.1. Research Principles
Research into semantic routing should be founded on regular Research into Semantic Routing should be founded on regular
scientific research principles [royalsoc]. Given the importance of scientific research principles [royalsoc]. Given the importance of
the Internet today, it is critical that research is targeted, the Internet today, it is critical that research is targeted,
rigorous, and reproducible. rigorous, and reproducible.
The most valuable research will go beyond an initial hypothesis, a The most valuable research will go beyond an initial hypothesis, a
report of the work done, and the results observed. Although that is report of the work done, and the results observed. Although that is
a required foundation, networking research needs to be independently a required foundation, networking research needs to be independently
reproducible so that claims can be verified or falsified. Further, reproducible so that claims can be verified or falsified. Further,
the networks on which the research is carried out need to both the networks on which the research is carried out need to both
reflect the characteristics that are being explicitly tested, and reflect the characteristics that are being explicitly tested, and
reproduce the variety of real networks that constitute the Internet. reproduce the variety of real networks that constitute the Internet.
Thus, when conducting experiments and research to address the Thus, when conducting experiments and research to address the
questions in Section 4.2, attention should be given to how the work questions in Section 4.2, attention should be given to how the work
is documented and how meaningful the test environment is, with a is documented and how meaningful the test environment is, with a
strong emphasis on making it possible for others to reproduce and strong emphasis on making it possible for others to reproduce and
validate the work. validate the work.
4.2. Routing Research Questions to be Addressed 4.2. Routing Research Questions to be Addressed
As research into the scenarios and possible uses of semantic routing As research into the scenarios and possible uses of Semantic Routing
progresses, a number of questions need to be answered. These progresses, a number of questions need to be answered. These
questions go beyond "Why do we need this function?" and "What could questions go beyond "Why do we need this function?" and "What could
we achieve by carrying additional semantic in an IP address?" The we achieve by carrying additional semantics in an IP address?" The
questions are also distinct from issues of how the additional questions are also distinct from issues of how the additional
semantics can be encoded within an IP address. All of those issues semantics can be encoded within an IP address. All of those issues
are, of course, important considerations in the debate about semantic are, of course, important considerations in the debate about Semantic
routing, but they form only part of the essential groundwork of Routing, but they form only part of the essential groundwork of
research into semantic routing itself. research into Semantic Routing itself.
This section sets out some of the concerns about how the wider the This section sets out some of the concerns about how the wider the
use of semantic routing might impact a routing system. These use of Semantic Routing might impact a routing system. These
questions need to be answered in separate research work or folded questions need to be answered in separate research work or folded
into the discussion of each semantic routing proposal. into the discussion of each Semantic Routing proposal.
1. What is the scope of the semantic routing proposal? This 1. What is the scope of the Semantic Routing proposal? This
question may lead to various answers: question may lead to various answers:
Global: It is intended to apply to all uses of IP. Global: It is intended to apply to all uses of IP.
Backbone: It is intended to apply to IP network connectivity. Backbone: It is intended to apply to IP network connectivity.
Overlay: It is to be used as an overlay network using tunneling Overlay: It is to be used as an overlay network using tunneling
over IP or other underlay technologies. over IP or other underlay technologies.
Gateway: The semantic routing will be used within a specific Gateway: The Semantic Routing will be used within a specific
domain, and communications with the wider Internet will be domain, and communications with the wider Internet will be
handled by IP and probably application gateways. handled by IP and probably application gateways.
Domain: The use of the semantic routing is strictly limited to Domain: The use of the Semantic Routing is strictly limited to
within a domain or private network. within a domain or private network.
Underlying this question is a broader question about the Underlying this question is a broader question about the
boundaries of the use of IP, and the limit of "the Internet". If boundaries of the use of IP, and the limit of "the Internet".
a limited domain is used, is it a semantic prefix domain If a limited domain is used, is it a semantic prefix domain
[RFC8799] where a part of the IP address space identifies the [RFC8799] where a part of the IP address space identifies the
domain so that an address is routable to the domain, but the domain so that an address is routable to the domain, but the
additional semantics are used only within the domain, or is the additional semantics are used only within the domain, or is the
address used exclusively within the domain so that the external address used exclusively within the domain so that the external
impact of the routability of the address and the additional impact of the routability of the address and the additional
semantics is not important? semantics is not important?
2. What will be the impact on existing routing systems? What would 2. What will be the impact on existing routing systems? What would
happen if a packet carrying additional semantics was subjected to happen if a packet carrying additional semantics was subjected
normal routing operations? How would the existing routing to normal routing operations? How would the existing routing
systems react if such a packet escaped (accidentally or systems react if such a packet escaped (accidentally or
maliciously) from the planned scope of the proposal? For maliciously) from the planned scope of the proposal? For
example: how are the semantic parts of an address distinguished example: how are the semantic parts of an address distinguished
from the routable parts (if, indeed, they are separable)?; is from the routable parts (if, indeed, they are separable)?; is
there an impact on the size and maintenance of routing tables due there an impact on the size and maintenance of routing tables
to the addition of semantics?; how are cryptographically due to the addition of semantics?; how are cryptographically
generated addresses (such as [RFC3972]) made routable and kept generated addresses (such as [RFC3972]) made routable and kept
simple enough for management?. simple enough for management?.
3. What path characteristics are needed to describe the desired 3. What path characteristics are needed to describe the desired
paths and as input to route computation? Since one of the paths and as input to route computation? Since one of the
implications of adding semantics to IP packets is to cause implications of adding semantics to IP packets is to cause
special processing by routers, it is important to understand what special processing by routers, it is important to understand
behaviors are wanted. Such path characteristics include (but are what behaviors are wanted. Such path characteristics include
not limited to): (but are not limited to):
Quality: Expressed in terms of throughput, latency, jitter, drop Quality: Expressed in terms of throughput, latency, jitter,
precedence, etc. drop precedence, etc.
Resilience: Expressed in terms of survival of network failures Resilience: Expressed in terms of survival of network failures
and delivery guarantees. and delivery guarantees.
Destination: How is a destination address to be interpreted if Destination: How is a destination address to be interpreted if
it encodes a choice of actual destinations? Can traffic be it encodes a choice of actual destinations? Can traffic be
forwarded over multiple distinct paths if multiple destination forwarded over multiple distinct paths if multiple
addresses are encoded? destination addresses are encoded?
Security: What choices of path reduce the vulnerability of the Security: What choices of path reduce the vulnerability of the
traffic to security or privacy attacks? traffic to security or privacy attacks?
In these cases, how do the routers utilize the additional In these cases, how do the routers utilize the additional
semantics to determine the desired characteristics? Or are such semantics to determine the desired characteristics? Or are such
characteristics used to feed the route computation logic, for characteristics used to feed the route computation logic, for
example, by means of metrics? What additional information about example, by means of metrics? What additional information about
the network do the routing protocols need to gather? What the network do the routing protocols need to gather? What
changes to the routing algorithm are needed to deliver packets changes to the routing algorithm are needed to deliver packets
according to the desired characteristics? How can routes be according to the desired characteristics? How can routes be
computed with characteristics that accommodate traffic patterns, computed with characteristics that accommodate traffic patterns,
requirements, and constraints? requirements, and constraints?
4. Can we solve these routing challenges with existing routing tools 4. Can we solve these routing challenges with existing routing
and methods? We can break this question into a set of more tools and methods? We can break this question into a set of
detailed questions. more detailed questions.
* Is new hardware needed? Existing deployed hardware has * Is new hardware needed? Existing deployed hardware has
certain assumptions about how forwarding is carried out based certain assumptions about how forwarding is carried out based
on IP addresses and routing tables. But hardware is on IP addresses and routing tables. But hardware is
increasingly programmable so that it may be possible to increasingly programmable so that it may be possible to
instruct the forwarding components to act on a variety of instruct the forwarding components to act on a variety of
elements of the packets. elements of the packets.
* Do we need new routing protocols? We might ask some * Do we need new routing protocols? We might ask some
subsidiary questions: subsidiary questions:
- Can we make do with existing protocols, possibly by tuning - Can we make do with existing protocols, possibly by tuning
configuration parameters or using them out of the box? configuration parameters or using them out of the box?
- Can we make backwards-compatible modifications to existing - Can we make backwards-compatible modifications to existing
protocols such that they work equally for today's IP protocols such that they work equally for today's IP
addresses or addresses with extra semantics? addresses or addresses with extra semantics?
- Do we need entirely new protocols or radical evolutions of - Do we need entirely new protocols or radical evolutions of
existing protocols in order to enforce advanced semantic existing protocols in order to enforce advanced Semantic
routing policies? Routing policies?
- Should we focus on the benefits of routing solutions that - Should we focus on the benefits of routing solutions that
are optimized for specific environments (network are optimized for specific environments (network
topologies, technologies, use cases), or should we attempt topologies, technologies, use cases), or should we attempt
to generalize to enable wider applicability? to generalize to enable wider applicability?
5. Do we need new management tools and techniques? How practical is 5. Do we need new management tools and techniques? How practical
it to debug and operate the routing system? Management of the is it to debug and operate the routing system? Management of
routing system (especially diagnostic management) is a crucial the routing system (especially diagnostic management) is a
and often neglected part of the problem space. A critical part crucial and often neglected part of the problem space. A
of this issue is how packets within the network can be inspected critical part of this issue is how packets within the network
by diagnostic tools (or human operators) and mapped to the can be inspected by diagnostic tools (or human operators) and
routing and forwarding decisions that were made within the mapped to the routing and forwarding decisions that were made
network in order to understand the actions made at and by within the network in order to understand the actions made at
upstream routers. and by upstream routers.
6. What is the impact of semantic routing on the security of the 6. What is the impact of Semantic Routing on the security of the
routing system? routing system?
* Does the introduction of semantic routing provide a greater * Does the introduction of Semantic Routing provide a greater
attack surface? attack surface?
* Can semantic routing provide greater opportunities for * Can Semantic Routing provide greater opportunities for
security by fine-grain forwarding of flows to be inspected by security by fine-grain forwarding of flows to be inspected by
different security functions? different security functions?
* Can semantic routing improve security and privacy by obscuring * Can Semantic Routing improve security and privacy by
information in the packets, or does the inclusion of obscuring information in the packets, or does the inclusion
additional information risk compromising security and privacy? of additional information risk compromising security and
privacy?
* To what extent does deployment within a limited domain * To what extent does deployment within a limited domain
strengthen security or make it less of a concern? strengthen security or make it less of a concern?
* Does the use of semantic routing make it easier or harder to * Does the use of Semantic Routing make it easier or harder to
impose censorship, prohibit access to the Internet by specific impose censorship, prohibit access to the Internet by
parties, or block access to certain resources or types of specific parties, or block access to certain resources or
service? types of service?
7. What is the scalability impact of semantic routing on routing 7. What is the scalability impact of Semantic Routing on routing
systems? Scalability can be measured as: systems? Scalability can be measured as:
* Routing table size. How many entries need to be maintained in * Routing table size. How many entries need to be maintained
the routing tables by different routers serving different in the routing tables by different routers serving different
roles in the network? Some approaches to semantic routing may roles in the network? Some approaches to Semantic Routing
be explicitly intended to address this problem. may be explicitly intended to address this problem.
* Forwarding table size. The size of the forwarding table may * Forwarding table size. The size of the forwarding table may
be less of an issue considering modern hardware, however the be less of an issue considering modern hardware, however the
more granular the routing/forwarding decisions made in a more granular the routing/forwarding decisions made in a
router, the greater the size of this table. The size of the router, the greater the size of this table. The size of the
forwarding table has implications for memory in the forwarding forwarding table has implications for memory in the
engine, but also for the lookup time for forwarding each forwarding engine, but also for the lookup time for
packet. forwarding each packet.
* Routing performance. Routing performance may be considered in * Routing performance. Routing performance may be considered
terms of the volume of data that has to be exchanged both to in terms of the volume of data that has to be exchanged both
construct and maintain the routing tables at the participating to construct and maintain the routing tables at the
routers. It may also be measured in terms of how much participating routers. It may also be measured in terms of
processing is required to compute new routes when there is a how much processing is required to compute new routes when
change in the network. there is a change in the network.
* Routing convergence. This is the time that it takes for a * Routing convergence. This is the time that it takes for a
routing protocol to discover changes (especially faults) in routing protocol to discover changes (especially faults) in
the network, to distribute the information about any changes the network, to distribute the information about any changes
to its peers, and to reach a stable state across the network to its peers, and to reach a stable state across the network
such that packets are forwarded consistently. such that packets are forwarded consistently.
For all questions about routing scalability, research that For all questions about routing scalability, research that
presents figures based on credible example networks is highly presents figures based on credible example networks is highly
desirable. Similar questions may be asked about the amount of desirable. Similar questions may be asked about the amount of
forwarding state that has to be maintained in the routers. forwarding state that has to be maintained in the routers.
8. To what extent can semantic routing be applied to multicast 8. To what extent can Semantic Routing be applied to multicast
transmission schemes: transmission schemes:
* Can semantic routing facilitate the computation and the * Can Semantic Routing facilitate the computation and the
establishment of (service-inferred) multicast distribution establishment of (service-inferred) multicast distribution
trees? trees?
* Can specific semantics be carried in multicast addresses? * Can specific semantics be carried in multicast addresses?
9. What aspects need to be standardized? It is important to 9. Is the approach extensible and maintainable? Can new features
understand the necessity of standardization within this research. be added without increasing the complexity and in a backward
What degree of interoperability is expected between devices and compatible way? Could the approach be modified to handle
networks? Is a given domain so constrained (for example, to a evolutions in the rest of the networking infrastructure?
single equipment vendor) that standardization would be Considerations might include the ability to encode additional
meaningless? Is the application so narrow (for example, in niche options or variants within protocol fields, and the ability to
hardware environments) such that interoperability is best handled add new fields. Such considerations must be actively traded
by agreements among small groups of vendors such as in industry against the processing overhead associated with certain encoding
consortia? types.
10. What aspects need to be standardized? It is important to
understand the necessity of standardization within this
research. What degree of interoperability is expected between
devices and networks? Is a given domain so constrained (for
example, to a single equipment vendor) that standardization
would be meaningless? Is the application so narrow (for
example, in niche hardware environments) such that
interoperability is best handled by agreements among small
groups of vendors such as in industry consortia?
5. Security and Privacy Considerations 5. Security and Privacy Considerations
Research into semantic routing must give full consideration to the Research into Semantic Routing must give full consideration to the
security and privacy issues that are introduced by these mechanisms. security and privacy issues that are introduced by these mechanisms.
Placing additional information into packet header fields might reveal Placing additional information into packet header fields might reveal
details of what the packet is for, what function the user is details of what the packet is for, what function the user is
performing, who the user is, etc. Furthermore, in-flight performing, who the user is, etc. Furthermore, in-flight
modification of the additional information might not directly change modification of the additional information might not directly change
the destination of the packet, but might change how the packet is the destination of the packet, but might change how the packet is
handled within the network and at the destination. handled within the network and at the destination.
It should also be considered how packet encryption techniques that It should also be considered how packet encryption techniques that
are increasingly popular for end-to-end or edge-to-edge security may are increasingly popular for end-to-end or edge-to-edge security may
obscure the semantic information carried in some fields of the packet obscure the semantic information carried in some fields of the packet
header or found deeper in the packet. This may render some semantic header or found deeper in the packet. This may render some semantic
routing techniques impractical and may dictate other methods of routing techniques impractical and may dictate other methods of
carrying the necessary information to enable semantic routing. carrying the necessary information to enable Semantic Routing.
6. IANA Considerations 6. IANA Considerations
This document makes no requests for IANA action. This document makes no requests for IANA action.
7. Acknowledgements 7. Acknowledgements
Thanks to Stewart Bryant for useful conversations. Luigi Iannone, Thanks to Stewart Bryant for useful conversations. Luigi Iannone,
Robert Raszuk, Dirk Trossen, Ron Bonica, Marie-Jose Montpetit, Yizhou Robert Raszuk, Dirk Trossen, Ron Bonica, Marie-Jose Montpetit, Yizhou
Li, Toerless Eckert, Tony Li, Joel Halpern, Stephen Farrell, Carsten Li, Toerless Eckert, Tony Li, Joel Halpern, Stephen Farrell, Carsten
Bormann, David Hutchison, Jeffery He, Dino Farinacci, and Greg Mirsky Bormann, David Hutchison, Jeffery He, Dino Farinacci, Greg Mirsky,
made helpful suggestions. and Jeff Haas made helpful suggestions.
This work is partially supported by the European Commission under This work is partially supported by the European Commission under
Horizon 2020 grant agreement number 101015857 Secured autonomic Horizon 2020 grant agreement number 101015857 Secured autonomic
traffic management for a Tera of SDN flows (Teraflow). traffic management for a Tera of SDN flows (Teraflow).
8. Contributors 8. Contributors
Joanna Dang Joanna Dang
Email: dangjuanna@huawei.com Email: dangjuanna@huawei.com
9. Informative References 9. Informative References
[I-D.farrel-irtf-introduction-to-semantic-routing] [I-D.farrel-irtf-introduction-to-semantic-routing]
Farrel, A. and D. King, "An Introduction to Semantic Farrel, A. and D. King, "An Introduction to Semantic
Routing", Work in Progress, Internet-Draft, draft-farrel- Routing", Work in Progress, Internet-Draft, draft-farrel-
irtf-introduction-to-semantic-routing-02, 14 January 2022, irtf-introduction-to-semantic-routing-03, 22 January 2022,
<https://www.ietf.org/archive/id/draft-farrel-irtf- <https://www.ietf.org/archive/id/draft-farrel-irtf-
introduction-to-semantic-routing-02.txt>. introduction-to-semantic-routing-03.txt>.
[I-D.king-irtf-semantic-routing-survey] [I-D.king-irtf-semantic-routing-survey]
King, D. and A. Farrel, "A Survey of Semantic Internet King, D. and A. Farrel, "A Survey of Semantic Internet
Routing Techniques", Work in Progress, Internet-Draft, Routing Techniques", Work in Progress, Internet-Draft,
draft-king-irtf-semantic-routing-survey-03, 26 November draft-king-irtf-semantic-routing-survey-03, 26 November
2021, <https://www.ietf.org/archive/id/draft-king-irtf- 2021, <https://www.ietf.org/archive/id/draft-king-irtf-
semantic-routing-survey-03.txt>. semantic-routing-survey-03.txt>.
[RFC3467] Klensin, J., "Role of the Domain Name System (DNS)", [RFC3467] Klensin, J., "Role of the Domain Name System (DNS)",
RFC 3467, DOI 10.17487/RFC3467, February 2003, RFC 3467, DOI 10.17487/RFC3467, February 2003,
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