IPv4 and IPv6 Options to support Information Centric Networking

In this memo we propose a new approach to Information Centric Networking , based on extending the IP protocol by using a new IP Option called CONET IP option (defined both for IPv4 and IPv6 ). The CONET IP option can be used by routers to support content aware networking, in addition to classical address based networking. The proposed solution has been described in . The CONET IP option is used to identify the content which is the object of the data transfer. Its usage allows efficient in-network caching and replication of content. The architecture foresees End-Nodes, Serving Nodes and CONET nodes (see ). End-Nodes request for content. Serving Nodes provide content. CONET nodes: i) forward content requests from End-Nodes to Serving Nodes; ii) deliver content from Serving Nodes to End-Nodes; iii) may cache content and therefore provide it to End-Nodes without contacting the Serving Node. CONET nodes can be further classified in Border Nodes and Internal nodes. Border Nodes are able to perform both "forward-by-name" and caching, Internal nodes are not able to perform "forward-by-name" (but only plain IP routing) and can only perform caching.

content is provided <------------------- +----+ +----+ +----+ | | --| |------| | +----+\ / +----+ +----+ \ +----+ +----+ / ----| |------| |/ +----+ +----+ End-Node legacy Intermediate Border Serving IP router Node Node Node | | +---------CONET next hop----------->+ | CONET Sub System (CCS) x | CCS y | ]]> As shown in , the CONET Information Centric Network can be seen as the inteconnection of CONET Sub Systems (CSSs). A CSS contains CONET nodes and exploits an under-CONET technology to transfer data among CONET nodes. A CSS could be: i) a couple of nodes interconnected by a point-to-point link, e.g. a PPP link or a UDP/IP overlay link; ii) a layer-2 network, e.g. Ethernet; iii) a layer-3 network, e.g. a private/public IPv4 or IPv6 network, or a whole IP Autonomous System, or even the whole current Internet. In addition to the new CONET IP option, the proposed solution needs a new Internet Protocol Number to identify the CONET protocol.

The CONET IPv4 option has the following format:

The CONET IPv6 option has the following format:

ppp : CONET Information Unit Type - This three bits field is used to differentiate between different types of CONET Information Units (CIUs)

LL : ICN-ID Length Specification - This two bits field provides the length of ICN Identifier (ICN-ID) field or specifies how the ICN-ID length is provided.

S : Sequence number indication - This one bit field tells if a chunk Sequence Number fiels is present in the Option after the ICN-ID field

C : cache indication - This one bit field is used to control cache operations.

Within Information Units that request for content (e.g. interest CIU), if the bit is set to "No cache" it indicates to the crossed nodes not to look for the content in the cache, but to forward the request toward the source. Within Information Units that carry content (e.g. named-data CIU), if the bit is set to "No cache" it indicates to the crossed nodes not to cache the content. r : reserved - This one bit field in the first byte after the option length is reserved. DS&T : Diffserv and Type - This one byte field is used to differentiate quality of services that can be provided by the network to the delivered content and to identify the content type. This field can be used to encode the content type and the priority as follows:

The righmost bit can be considere as a flag F. If the flag bit F is set to 0 the three rightmost bits encode 8 priority levels and other 4 bits are for the content-type. If the flag bit is set to one, no preallocated semantic to the remaining bits is given. ICN-ID : ICN Identifier (ICN-ID) field - The ICN-ID is a unique identifier for the content. The ICN-ID is carried in the ICN-ID field. How to determine the length of this field is defined by the ICN-ID Length Specification field. If the ICN-ID Length Specification field determines the field length, the ICN-ID field only carries the ICN-ID. If the ICN-ID Length Specification field indicates that the field length is carried in the field itself, the ICN-ID field starts with a one byte field that determines its length.

The ICN-ID starts with a two bytes field called ICN-ID namespace ID that determines the structure of the rest of the ICN-ID. ICN-ID namespace values needs to be assigned by the IANA. Note that in most circumstances, the ICN-ID can be processed by the routers as an opaque object, as described in . This is why the ICN-ID namespace ID has been included at the beginning of the ICN-ID itself. In other cases the nodes are requested to perform a forward-by-name procedure, which may require a semantic understanding of the ICN-ID.

CSN : Chunk Sequence Number - This optional field carries the Chunk Sequence Number that identifies a portion of the content. When a content is split in a sequence of smaller unit called "chunks", this field can explitly carry the sequence number of the chunk (another solution is obvioulsy to embed the chunk number in the ICN-ID). The Chunk Sequence Number is represented with a variable number of bytes. An initial bit pattern determines the length of the CSN field.

Binary patterns from 11110010 to 11111111 are reserved. They can be used to extend the CSN range if needed. With the above defined option, we can have up to 2^40 chunks in a content. Assuming a relatively small chunk size of 1 KBytes, it is possible to have a content of 1099 TeraBytes, while assuming a more reasonable chunk size of 256 Kbyte it is possible to have a content of 281474 TeraBytes (218 PetaBytes). The rationale for having a variable length encoding is the following. The CSN range for a given content is determined by the content size divided by the chunk size. As content of very different sizes can be transmitted, the CSN range can be very different. Therefore it is not efficient to dimension this field considering the maximum number of chunks in which a content can be split.

The IPv6 CONET option has to be interpreted by all routers in the path that are ICN capable. Therefore we it naturally fits into the the IPv6 Hop-by-hop header, which is the first extension header that can be present after the fixed part of the header. The Hop-by-hop header is meant to be read by all routers in the path.

In the previous section, we have seen the description of the CONET IP option that is carried in the header of IP packets. The payload of IP packets is the CONET protocol and a specific IP protocol number is assigned to it: CONET IP protocol number : xxx (to be assigned by IANA). The figure below shows the CONET protocol stack. CONET protocol is divided in two sub-layers, whose data unit are respectively denoted as "Carrier Packets" and "CONET Information Units". A CONET Information Unit (CIU) can be split into different Carrier Packets. Each Carrier Packet is transported by an IP packet. There are different types of CONET Information Units, the CIU type information is carried in the CONET Information Unit Type field in the CONET IP option.

The generic structure of a Carrier Packet (CP) is reported hereafter:

The information contained in the CP Payload header is specific for each CIU type and can depend on the "transport" protocol. It will be described in other specification documents. The definition of an ICN transport protocol caller RDITP (Receiver Driven ICN Transport Protocol) is proposed in . The CP payload header contains the length of the CP Payload and allows to identify the start of the CP Path state field. The CP Path state field is used in End-Nodes, Border Nodes and Serving Nodes to assist in the forwarding operation of carrier packet, therefore it is described here. The CP Path State field stores the End-Node address and the addresses of the set of crossed Border Nodes in the path from End-Node to the Serving Node (or to a border or Intermediate Node that provides a requested content). The format of the CP path state field is reported hereafter (assuming that IPv4 addresses are carried).

The length field specifies the length of the CP Path State field in bytes. If the first bit of the len field is 0, the remaining 7 bits of the first byte are used as len field and both the length field and the pointer field are one byte length. In this case the maximum value of the length of the CP Path State field is 127. If the first bit of the len field is 1, both the length field and the pointer field are two bytes length. In this case the maximum value of the length of the CP Path State field is 32767. The pointer field specifies the offset, starting from the start of the CP Path State field where the last address has been inserted. Each address is represented as a couple (ad-type, address) it could be represented by a triple (ad-type, ad-length, address) if the address type is of variable length. The ad-type field is one byte size and currently admitted values are:

An end-node that wants to retrieve a content (or better a Chunk of a content) issues an Interest CIU, the ICN-ID and the Chunk Sequence Number of the required Content are respectively transported in the ICN Identifier (ICN-ID) field and in the CSN field of the CONET IP option. The end-node stores its IP address in CP path state field, initializing the pointer field. Assuming for simplicity that the Interest CIU will fit into a single Carrier Packet, the Interest CIU will be included in the Carrier Packet that in turn is inserted into an IP packet. The end-node must now determine the destination IP address for the Carrier Packet. The end-node performs a forward-by-name operation, trying to associate the ICN-ID with a next hop (i.e. with the IP address of the next hop). The next hop can be the Serving Node (if the Serving Node is in the same CONET Sub System of the end-node) or a Border Node of the CONET Sub System (if the Serving Node is in a different CONET Sub System). Typically the End-Node does not participate to the content routing protocols, therefore it cannot resolve the ICN-ID into the address of the next hop, but it has to ask an external entity, behaving in a similar way of a current name server (such external entity could be a part of a system that handles the content routing, called Routing Name System). Once this information is retrieved, the end-note can fill the IP destination address in the IP header and sends the packet. The end-node may cache the mapping (ICN-ID -> next hop) into its memory as well.

If the Serving Node is in the same CONET than the end-node, the Serving Node IP address will be used a destination IP address by the end-node. The Serving Node will receive an IP packet directed to itself, whose IP protocol number is "CONET". Therefore the packet will be internally dispatched toward the "CONET entity" in the Serving Node. The CONET entity reads the CONET information unit type from the CONET IP options and recognizes that the received packet is an interest packet. Then it reads the ICN-ID and Chunk Sequence Number in the CONET IP option, the ICN-ID will correspond to a content provided by the Serving Node. The CONET entity will then process the CONET transport protocol information carried in the IP payload, which may for example specify a requested offset within the chunk. Finally the CONET entity will respond to the interest packet by sending the requested named-data CIU.

If the Serving Node is in a different CONET Sub System than the end-node, the address of a CONET Border Node will be used a destination IP address by the end-node. The Border Node will receive an IP packet directed to itself, whose IP protocol number is "CONET". Therefore the packet will be internally dispatched toward the "CONET entity" in the Border Node. The CONET entity reads the CONET information unit type from the CONET IP options and recognizes that the received packet is an interest packet. Then it reads the ICN-ID and Chunk Sequence Number in the CONET IP option and is able to understand which content and which part of the available content it needs to provide. If the Cache indication field is set to "No Cache" or if the field is set to "Cache" but the chunk is not available in the cache, the Border Node starts the forward-by-name process. It will resolve the next hop of the interest packet, which can be a Serving Node in a different CONET Sub System (with respect to the one from which the interest packet was received) connected to the Border Node, or another Border Node in the path toward the Serving Node. Before sending out the packet, the Border Node adds its IP address in the CP Path State field and updates the pointer field. Note that these procedures needs to be performed in the "fast path" of the Border Node (in this case the CONET entity in the Border Node can be seen as an integral part of the enhanced IP protocol). If the Cache indication field is set to "Cache" and the Border Node has found that the chunk corresponding to the ICN-ID/CSN is available in its cache, the Border Node will process the CONET transport protocol information carried in the IP payload, which may for example specify a requested offset within the chunk and it will respond to the interest packet by sending the requested named-data CIU.

When a packet is sent to the CONET next hop (as selected by the End-Node or by a Border Node) using the IP destination address of the next hop resolved by the forward-by-name, it can cross different IP routers in the path from the sending node and the next hop. A crossed router that is aware of the CONET IP option, is a CONET Intermediate Node. This node may have cached the the chunk that is requested by the interest packet. The Intermediate Node works as follows. When processing the IP header for the received packet, it finds that the packet contains the CONET IP option. If the Cache indication field is set to "No Cache", the Intermediate Node forwards the packet using the destination IP address. If the Cache indication field is set to "Cache", the Intermediate Node checks the presence of the chunk in its cache before forwarding the IP packet. Therefore, it reads the ICN-ID and Chunk Sequence Number in the CONET IP option and checks if the chunk is present in its cache. If the chunk is not present, the normal IP processing is continued. Note that these operations needs to be performed in the "fast path" of the router and they only require information that is transported in the IP option. If the chunk is present in the CONET router cache, the router will process the CONET transport protocol information carried in the IP payload, which may for example specify a requested offset within the chunk and it will respond to the interest packet by sending the requested named-data CIU.

The responding node is the node that is able to provide a content (identified by ICN-ID and Chunk Sequence Number) to a requesting end-node. Therefore the responding node can be a Serving Node which provides an original copy of the content, or a Border Node / Intermediate Node that provide a cached copy of the content. The responding node will use the Path State information contained in the received carrier packet carrying the Interest CIU to forward back the carrier packets containing the named-data CIU towards the requesting end-node. In particular, it will use the pointer field to read the last address in the list and will use it as IP destination address for the Carrier packet carrying the named-data CIU. We can denote this address as "CONET previous hop". Then it will update the pointer field so that the next node will use the previous address in the list. It may choose to strip the used address from the list in the CP Path state, thereby reducing the CP Path State field length.

The Border Node will receive an IP packet directed to itself, whose IP protocol number is "CONET". Therefore the packet will be internally dispatched toward the "CONET entity" in the Border Node. The CONET entity reads the CONET information unit type from the CONET IP options and recognizes that the received packet is a named-data packet. Again, we stress that this processing should be performed in the fast path. Being a named-data packet, the Border Node will read the CP Path State field in the Carrier Packet and by using the pointer field will identify the CONET previous hop in the path towards the requesting end-node. Before sending out the packet, it will update the pointer field in the CP Path State field. The destination IP address of the packet will be set to the CONET previous hop retrieved from the CP Path State field. If the Cache indication bit in the IP option is set to "Cache", the Border Node may choose to cache the CIU that is transported by the carried packet. In this case, it is reccomended that the Border Node dispatches the packet as soon as possible and operates on a local copy to perform cache related operations.

An Intermediate Node, i.e. a router in the path between a Serving Node or a Border Node and the CONET previous hop, which is aware of the CONET option, may decide to cache the named data CIU transported by a carrier packet. The Intermediate Node will receive an IP packet with an IP destination equal to the CONET previous hop and will immediately forward this packet using IP routing. Then, if the Cache indication bit in the IP option is set to "Cache", the Intermediate Node may choose to cache the CIU that is transported by the carried packet.

When a packet is sent to the CONET previous hop (as selected by the Serving Node or by a Border Node) using the IP destination address of the previous hop obtained using the CP Path State information, it can cross different IP routers in the path from the sending node and the previous hop. If a crossed router is a legacy router not aware of the CONET IP option, it will simply forward the packet looking at the IP destination address. Note that a requirement for such legacy router is to be configured not to drop IP packets carrying unidentified IP options.

The forward-by-name process is performed in the end-node and in Border Nodes in order to resolve a ICN-ID into the next hop towards a Serving Node for the given ICN-ID. This document provides a framework under which the forward-by-name procedures can be performed, and assures that different forward-by-name procedures and approaches may coexist. These different approaches needs to be separately specified. The format and the semantic of the ICN-ID may need to be specified when defining a specific forward-by-name approach. This is made possible by the concept of ICN-ID name space ID, which is carried within the ICN-ID. The basic procedure that a forward-by-name framework needs to offer is called resolveICN-ID, it takes as input the ICN-ID and returns the next_hop_address. This procedure is performed by end-nodes and by Border Nodes that are not able to provide a cached response for a content requested by an End-Node. resolveICN-ID (ICN-ID) -> next_hop_address The tables on which the forward-by-name procedures are based are populated by Serving Nodes and by Border Nodes. The procedure is initiated by Serving Nodes that advertize the hosted content with the advertizeICN-ID procedure. In turn, the procedure is replicated by the Border Nodes that spread the received advertising toward other Border Nodes. This procedure takes as input a ICN-ID, the address of the node performing the procedure, and the path information towards the Serving Node as seen by the node performing the procedure. Depending on the specific content routing approach, the path information can be simply an hop count, or it could be the path list (as in the BGP AS-PATH). advertizeICN-ID (ICN-ID, node_address, path_info) In the following section we define two CONET default name spaces. It could be more appropriate that in future version of this document this specification is provided in a separate document.

We define two default ICN-ID name spaces for CONET, one is based on variable length strings as ICN-ID, as it was proposed in , the second one is based on fixed length hashes. The two namespaces are assigned the following ICN-ID name space IDs.

In the VLL (Variable Length Label) CONET namespace the ICN-ID is simply the string representation of a resource. As described in ICN-IDs are hierarchically structured so that an individual name is composed of a number of components (see for further details. An authority is needed to ensure the uniqueness of the ICN-IDs. The approach should be similar on how the uniqueness of DNS names is granted in today's Internet. In the Principal/Label Hash Based CONET namespace the ICN-ID is the composition of two hash values, as follows: ICN-ID = ( hash (Principal) , hash (Label) ) In the Principal/Label Hash Based CONET namespace the Hash(principal) is a 8 bytes hash of a string representing the Principal. The Label is a 6 bytes hash of a string representing the label. A central authority is needed to ensure the uniqueness of the Hash(principal), i.e. a Principal cannot be assigned if its hash collides with an already assigned hash. The Principal is responsible to ensuring that each Hash(Label) belonging to the Principal are unique. Therefore a Label cannot be used by a Principal if its hash collides with the Hash of an already used Label.

We acknowledge the financial support by the EU in the context of the CONVERGENCE research project.

IP Options have often been criticized because their support in current routers would impose a performance penalty, but we can assume here that routers will be modified to support Information Centric Networking. Compared with "clean slate" approaches where CCN nodes could be completely different with respect to routers, we believe that we are able to provide all the functionality we need for Information Centric Networking, with reasonable modification in router architectures and preserving all the functionality of current IP networking.

This document requires the allocation of one IP option by the IANA. This document requires the allocation of one IP protocol number by the IANA. This document requires that IANA will maintain the registry of CONET namespaces.

Security considerations to be provided