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Host Identity Protocol (HIP) Multi-Hop Routing Extension
RFC 6028

Document Type RFC - Experimental (October 2010)
Authors Gonzalo Camarillo , Ari Keränen
Last updated 2015-10-14
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
IESG Responsible AD Ralph Droms
Send notices to (None)
RFC 6028
Internet Engineering Task Force (IETF)                      G. Camarillo
Request for Comments: 6028                                    A. Keranen
Category: Experimental                                          Ericsson
ISSN: 2070-1721                                             October 2010

        Host Identity Protocol (HIP) Multi-Hop Routing Extension


   This document specifies two extensions to the Host Identity Protocol
   (HIP) to implement multi-hop routing.  The first extension allows
   implementing source routing in HIP.  That is, a node sending a HIP
   packet can define a set of nodes that the HIP packet should traverse.
   The second extension allows a HIP packet to carry and record the list
   of nodes that forwarded it.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  It represents the consensus of the IETF
   community.  It has received public review and has been approved for
   publication by the Internet Engineering Steering Group (IESG).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................3
      2.1. Requirements Language ......................................3
      2.2. Definitions ................................................3
   3. Protocol Definitions ............................................3
      3.1. Creating and Processing Via Lists ..........................4
      3.2. Creating Destination Lists .................................4
      3.3. Processing Destination Lists ...............................5
      3.4. Fragmentation Considerations ...............................5
   4. Packet Formats ..................................................5
      4.1. Source and Destination Route List Parameters ...............6
   5. IANA Considerations .............................................7
   6. Security Considerations .........................................8
      6.1. Forged Destination and Via Lists ...........................8
      6.2. Forwarding Loops ...........................................8
   7. Acknowledgments .................................................9
   8. References ......................................................9
      8.1. Normative References .......................................9
      8.2. Informative References .....................................9

1.  Introduction

   When the Host Identity Protocol (HIP) [RFC5201] is used in certain
   contexts, nodes need the ability to perform source routing.  That is,
   a node needs the ability to send a HIP signaling packet that will
   traverse a set of nodes before reaching its destination.  Such
   features are needed, e.g., in the HIP-Based Overlay Networking
   Environment (HIP BONE) [HIP-BONE] or if two nodes wish to keep a
   third, or more, HIP nodes on the signaling path.  This document
   defines an extension that provides HIP with this functionality.

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   Additionally, when HIP signaling packets are routed through multiple
   nodes, some of these nodes (e.g., the destination host) need the
   ability to know the nodes that a particular packet traversed.  This
   document defines another extension that provides HIP with this

   These two extensions enable multi-hop routing in HIP.  Before these
   extensions were specified, there were standardized ways for
   supporting only a single intermediate node (e.g., a rendezvous server
   [RFC5204]) between the source of a HIP packet and its destination.

2.  Terminology

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.2.  Definitions

   The following terms used in this document are similar to those
   defined by REsource LOcation And Discovery (RELOAD) [P2PSIP-BASE] but
   are used here in the context of HIP.

   Destination list:  A list of Host Identity Tags (HITs) of the nodes
      that a HIP packet should traverse.

   Via list:  A list of HITs of the nodes that a HIP packet has

   Symmetric routing:  A response to a message is routed back using the
      same set of intermediary nodes as the original message used,
      except in reversed order.  Also known as symmetric recursive

3.  Protocol Definitions

   The multi-hop routing extensions may be used in different contexts,
   and whether a new HIP signaling packet should, for example, include a
   Via list or have different options enabled can depend on the
   particular use case, local policies, and different protocols using
   the extension.  This section defines how the new parameters are
   handled, but when to use these extensions, or how to configure them,
   is out of scope for this document.

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3.1.  Creating and Processing Via Lists

   When a node sending a HIP packet needs to record the nodes that are
   on the path that the HIP packet traverses, it includes an empty
   ROUTE_VIA parameter in the packet.

   A node that receives a packet with a ROUTE_VIA parameter SHOULD add
   its own HIT to the end of the ROUTE_VIA parameter, unless it is the
   final recipient of the packet.  If the node uses a different HIT on
   the HIP association it used for receiving the packet than for sending
   it forward, it SHOULD also add the receiving HIT to the route list
   before the sending HIT.

   If the node is the final recipient of the packet, and the received
   packet generates a response HIP packet, the node checks the SYMMETRIC
   flag from the ROUTE_VIA parameter.  If the SYMMETRIC flag is set, the
   node MUST create a ROUTE_DST parameter from the ROUTE_VIA parameter,
   as described in Section 3.2, and include it in the response packet.
   Also, if an intermediary node generates a new HIP packet (e.g., an
   error NOTIFY packet) due to a HIP packet that had a ROUTE_VIA
   parameter with the SYMMETRIC flag set, and the new packet is intended
   for the sender of the original HIP packet, the node SHOULD construct
   and add a ROUTE_DST parameter into the new packet as in the previous

3.2.  Creating Destination Lists

   A node that needs to define the other nodes that should be on the
   path a HIP packet traverses adds a ROUTE_DST parameter to the HIP
   packet.  The node may either decide the path independently, or it may
   create the path based on a ROUTE_VIA parameter.  Only the originator
   of a signed HIP packet can add a ROUTE_DST parameter to the HIP
   packet, and none of the nodes on the path can modify it, since the
   parameter is covered by the signature.

   When a node creates a ROUTE_DST parameter due to receiving a packet
   with a ROUTE_VIA parameter, it copies all the HITs in the ROUTE_VIA
   parameter to the ROUTE_DST parameter, but in reversed order.  This
   results in the HIP response packet being forwarded using the same
   path as the packet for which the response was generated.  If exactly
   the same set of nodes should be traversed by the response packet, the
   MUST_FOLLOW flag (see Table 1) also SHOULD be set in the ROUTE_VIA
   parameter (and eventually copied to the ROUTE_DST parameter) to
   prevent the response packet from possibly skipping some nodes on the

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3.3.  Processing Destination Lists

   When a node receives a HIP packet that contains a ROUTE_DST
   parameter, it first looks up its own HIT from the route list.  If the
   node's own HIT is not in the list and the node is not the receiver of
   the packet, the packet was incorrectly forwarded and MUST be dropped.
   If the node's HIT is in the list more than once, the list is invalid
   and the packet MUST be dropped to avoid forwarding loops.  The next
   hop for the packet is the HIT after the node's own HIT in the list.
   If the node's HIT was the last HIT in the list, the next hop is the
   receiver's HIT in the HIP header.

   If the MUST_FOLLOW flag in the ROUTE_DST parameter is not set, the
   node SHOULD check whether it has a valid locator for one of the nodes
   later in the list, or for the receiver of the packet, and it MAY
   select such a node as the next hop.  If the MUST_FOLLOW flag is set,
   the node MUST NOT skip any nodes in the list.

   If the node has a valid locator for the next hop, it MUST forward the
   HIP packet to the next-hop node.  If the node cannot determine a
   valid locator for the next-hop node, it SHOULD drop the packet and
   SHOULD send back a NOTIFY error packet with type UNKNOWN_NEXT_HOP
   (value 90).  The Notification Data field for the error notifications
   SHOULD contain the HIP header of the rejected packet and the
   ROUTE_DST parameter.

3.4.  Fragmentation Considerations

   Via and Destination lists with multiple HITs can substantially
   increase the size of the HIP packets, and thus fragmentation issues
   (see Section 5.1.3 of [RFC5201]) should be taken into consideration
   when these extensions are used.  Via lists in particular should be
   used with care, since the final size of the packet is not known
   unless the maximum possible amount of hops is known beforehand.  Both
   parameters do still have a maximum size based on the maximum number
   of allowed HITs (see Section 4.1).

4.  Packet Formats

   This memo defines two new HIP parameters that are used for recording
   a route via multiple nodes (ROUTE_VIA) and for defining a route that
   a packet should traverse by the sender of the packet (ROUTE_DST).

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   The ROUTE_DST parameter is integrity protected with the signature
   (where present) but ROUTE_VIA is not, so that intermediary nodes can
   add their own HITs to the list.  Both ROUTE_DST and ROUTE_VIA are
   critical parameters (as defined in Section 5.2.1 of [RFC5201]), since
   the packet will not be properly routed unless all nodes on the path
   recognize the parameters.

4.1.  Source and Destination Route List Parameters

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |             Type              |             Length            |
     |             Flags             |            Reserved           |
     |                                                               |
     |                            HIT #1                             |
     |                                                               |
     |                                                               |
     .                               .                               .
     .                               .                               .
     |                                                               |
     |                            HIT #n                             |
     |                                                               |
     |                                                               |

     Type      ROUTE_DST: 4601
               ROUTE_VIA: 64017
     Length    length in octets, excluding Type and Length
               (i.e., number-of-HITs * 16 + 4)
     Flags     bit flags that can be used for requesting special
               handling of the parameter
     Reserved  reserved for future use
     HIT       Host Identity Tag of one of the nodes on the path

        Figure 1.  Format of the ROUTE_VIA and ROUTE_DST Parameters

   Figure 1 shows the format of both ROUTE_VIA and ROUTE_DST parameters.
   The ROUTE_DST parameter, if present, MUST have at least one HIT, but
   the ROUTE_VIA parameter can also have zero HITs.  The ROUTE_DST and
   ROUTE_VIA parameters SHALL NOT contain more than 32 HITs.  The Flags

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   field is used for requesting special handling for Via and Destination
   lists.  The flags defined in this document are shown in Table 1.  The
   Reserved field can be used by future extensions; it MUST be zero when
   sending and ignored when receiving this parameter.

   | Pos | Name        | Purpose                                       |
   |  0  | SYMMETRIC   | The response packet MUST be sent with a       |
   |     |             | ROUTE_DST list made from the ROUTE_VIA list   |
   |     |             | containing this flag, i.e., using symmetric   |
   |     |             | routing.                                      |
   |  1  | MUST_FOLLOW | All the nodes in a ROUTE_DST list MUST be     |
   |     |             | traversed, i.e., even if a node would have a  |
   |     |             | valid locator for a node beyond the next hop, |
   |     |             | it MUST NOT forward the packet there but to   |
   |     |             | the next-hop node.                            |

         Table 1.  Bit Flags in ROUTE_VIA and ROUTE_DST Parameters

   The "Pos" column in Table 1 shows the bit position of the flag (as in
   Figure 1) in the Flags field, "Name" gives the name of the flag used
   in this document, and "Purpose" gives a brief description of the
   meaning of that flag.

   The flags apply to both ROUTE_VIA and ROUTE_DST parameters, and when
   a ROUTE_DST parameter is added to a packet because of a ROUTE_VIA
   parameter, the same flags MUST be copied to the ROUTE_DST parameter.

5.  IANA Considerations

   This section is to be interpreted according to [RFC5226].

   This document updates the IANA Registry for HIP Parameter Types
   [RFC5201] by assigning new HIP Parameter Type values for the new HIP
   Parameters: ROUTE_VIA and ROUTE_DST (defined in Section 4).  This
   document also defines a new Notify Packet Type [RFC5201],
   UNKNOWN_NEXT_HOP, in Section 3.3.

   The ROUTE_DST and ROUTE_VIA parameters utilize bit flags, for which
   IANA has created and now maintains a new sub-registry entitled "HIP
   Via Flags" under the "Host Identity Protocol (HIP) Parameters"
   registry.  Initial values for the registry are given in Table 1;
   future assignments are to be made through IETF Review or IESG
   Approval [RFC5226].  Assignments consist of the bit position and the
   name of the flag.

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6.  Security Considerations

   The standard HIP mechanisms (e.g., using signatures, puzzles, and the
   ENCRYPTED parameter [RFC5201]) provide protection against
   eavesdropping; replay; message insertion, deletion, and modification;
   and man-in-the-middle attacks.  Yet, the extensions described in this
   document allow nodes to route HIP messages via other nodes and hence
   possibly try to mount Denial-of-Service (DoS) attacks against them.
   The following sections describe possible attacks and means to
   mitigate them.

6.1.  Forged Destination and Via Lists

   The Destination list is protected by the HIP signature so that the
   receiver of the message can check that the list was indeed created by
   the sender of the message and not modified on the path.  Also, the
   nodes forwarding the message MAY check the signature of the forwarded
   packets if they have the Host Identity (HI) of the sender (e.g., from
   an I2 or R1 message [RFC5201]) and drop packets whose signature check
   fails.  With forwarding nodes checking the signature and allowing
   messages to be forwarded only from nodes for which there is an active
   HIP association, it is also possible to reliably identify attacking

   The limited amount of HITs allowed in a Destination list limits the
   impact of attacks using a forged Destination list, and the attacker
   also needs to know a set of HIP nodes that are able to route the
   message hop-by-hop for the attack to be effective.

   A forged Via list results in a similar attack as with the Destination
   list and with similar limitations.  However, in this attack the
   Destination list generated from the Via list is validly signed by the
   responding node.  To limit the effect of this kind of attack, a
   responding node may further decrease the maximum acceptable number of
   nodes in the Via lists or allow only certain HITs in the lists.
   However, using these mechanisms requires either good knowledge of the
   overlay network (i.e., maximum realistic amount of hops) or knowing
   the HITs of all potential nodes forwarding the messages.

6.2.  Forwarding Loops

   A malicious node could craft a destination route list that contains
   the same HIT more than once and thus create a forwarding loop.  The
   check described in Section 3.3 should break such loops, but nodes MAY
   in addition utilize the OVERLAY_TTL [HIP-BONE] parameter for
   additional protection against forwarding loops.

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7.  Acknowledgments

   Tom Henderson provided valuable comments and improvement suggestions
   for this document.

8.  References

8.1.  Normative References

   [RFC2119]      Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5201]      Moskowitz, R., Nikander, P., Jokela, P., Ed., and T.
                  Henderson, "Host Identity Protocol", RFC 5201, April

8.2.  Informative References

   [RFC5204]      Laganier, J. and L. Eggert, "Host Identity Protocol
                  (HIP) Rendezvous Extension", RFC 5204, April 2008.

   [RFC5226]      Narten, T. and H. Alvestrand, "Guidelines for Writing
                  an IANA Considerations Section in RFCs", BCP 26, RFC
                  5226, May 2008.

   [HIP-BONE]     Camarillo, G., Nikander, P., Hautakorpi, J., Keranen,
                  A., and A. Johnston, "HIP BONE: Host Identity Protocol
                  (HIP) Based Overlay Networking Environment", Work in
                  Progress, June 2010.

   [P2PSIP-BASE]  Jennings, C., Lowekamp, B., Ed., Rescorla, E., Baset,
                  S., and H. Schulzrinne, "REsource LOcation And
                  Discovery (RELOAD) Base Protocol", Work in Progress,
                  March 2010.

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Authors' Addresses

   Gonzalo Camarillo
   Hirsalantie 11
   02420 Jorvas


   Ari Keranen
   Hirsalantie 11
   02420 Jorvas


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