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
Abstract
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
evaluation.
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
http://www.rfc-editor.org/info/rfc6028.
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Copyright Notice
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document authors. All rights reserved.
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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
functionality.
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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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
traversed.
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
routing.
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
case.
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
list.
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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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RFC 6028 HIP Multi-Hop Routing Extension October 2010
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
nodes.
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
2008.
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
Ericsson
Hirsalantie 11
02420 Jorvas
Finland
EMail: Gonzalo.Camarillo@ericsson.com
Ari Keranen
Ericsson
Hirsalantie 11
02420 Jorvas
Finland
EMail: Ari.Keranen@ericsson.com
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