Network Working Group T. Henderson, Ed.
Internet-Draft The Boeing Company
Intended status: Standards Track C. Vogt
Expires: January 15, 2013 J. Arkko
Ericsson Research NomadicLab
July 14, 2012
Host Multihoming with the Host Identity Protocol
draft-ietf-hip-multihoming-01
Abstract
This document defines host multihoming extensions to the Host
Identity Protocol (HIP), by leveraging protocol components defined
for host mobility.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 15, 2013.
Copyright Notice
Copyright (c) 2012 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
(http://trustee.ietf.org/license-info) 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.
Henderson, et al. Expires January 15, 2013 [Page 1]
Internet-Draft HIP Multihoming July 2012
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction and Scope . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Conventions . . . . . . . . . . . . . . . . . 4
3. Protocol Model . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Operating Environment . . . . . . . . . . . . . . . . . . 5
3.2. Multihoming Overview . . . . . . . . . . . . . . . . . . . 7
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Host Multihoming . . . . . . . . . . . . . . . . . . . . . 8
4.2. Site Multihoming . . . . . . . . . . . . . . . . . . . . . 9
4.3. Dual host multihoming . . . . . . . . . . . . . . . . . . 10
4.4. Combined Mobility and Multihoming . . . . . . . . . . . . 10
4.5. Initiating the Protocol in R1 or I2 . . . . . . . . . . . 11
5. Other Considerations . . . . . . . . . . . . . . . . . . . . . 12
5.1. Address Verification . . . . . . . . . . . . . . . . . . . 12
5.2. Preferred Locator . . . . . . . . . . . . . . . . . . . . 12
5.3. Interaction with Security Associations . . . . . . . . . . 13
6. Processing Rules . . . . . . . . . . . . . . . . . . . . . . . 15
6.1. Sending LOCATORs . . . . . . . . . . . . . . . . . . . . . 15
6.2. Handling Received LOCATORs . . . . . . . . . . . . . . . . 17
6.3. Verifying Address Reachability . . . . . . . . . . . . . . 19
6.4. Changing the Preferred Locator . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 20
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
9. Authors and Acknowledgments . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative references . . . . . . . . . . . . . . . . . . . 20
10.2. Informative references . . . . . . . . . . . . . . . . . . 21
Appendix A. Document Revision History . . . . . . . . . . . . . . 21
Henderson, et al. Expires January 15, 2013 [Page 2]
Internet-Draft HIP Multihoming July 2012
1. Introduction and Scope
The Host Identity Protocol [RFC4423] (HIP) supports an architecture
that decouples the transport layer (TCP, UDP, etc.) from the
internetworking layer (IPv4 and IPv6) by using public/private key
pairs, instead of IP addresses, as host identities. When a host uses
HIP, the overlying protocol sublayers (e.g., transport layer sockets
and Encapsulating Security Payload (ESP) Security Associations (SAs))
are instead bound to representations of these host identities, and
the IP addresses are only used for packet forwarding. However, each
host must also know at least one IP address at which its peers are
reachable. Initially, these IP addresses are the ones used during
the HIP base exchange [RFC5201].
One consequence of such a decoupling is that new solutions to
network-layer mobility and host multihoming are possible. Host
mobility is defined in [I-D.ietf-hip-rfc5206-bis] and covers the case
in which a host has a single address and changes its network point-
of-attachment while desiring to preserve the HIP-enabled security
association. Host multihoming is somewhat of a dual case to host
mobility, in that a host may simultaneously have more than one
network point-of-attachment. There are potentially many variations
of host multihoming possible. The scope of this document encompasses
messaging and elements of procedure for some basic host multihoming
scenarios of interest.
Another variation of multihoming that has been heavily studied site
multihoming. Solutions for site multihoming in IPv6 networks have
been specified by the IETF shim6 working group. The shim6 protocol
[RFC5533] bears many architectural similarities to HIP but there are
differences in the security model and in the protocol. Future
versions of this draft will summarize the differences more
completely.
While HIP can potentially be used with transports other than the ESP
transport format [RFC5202], this document largely assumes the use of
ESP and leaves other transport formats for further study.
There are a number of situations where the simple end-to-end
readdressing functionality defined herein is not sufficient. These
include the initial reachability of a multihomed host, location
privacy, simultaneous mobility of both hosts, and some modes of NAT
traversal. In these situations, there is a need for some helper
functionality in the network, such as a HIP rendezvous server
[RFC5204]. Such functionality is out of the scope of this document.
Finally, making underlying IP multihoming transparent to the
transport layer has implications on the proper response of transport
congestion control, path MTU selection, and Quality of Service (QoS).
Henderson, et al. Expires January 15, 2013 [Page 3]
Internet-Draft HIP Multihoming July 2012
Transport-layer mobility triggers, and the proper transport response
to a HIP multihoming address change, are outside the scope of this
document.
2. Terminology and Conventions
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].
Terminology is copied from [I-D.ietf-hip-rfc5206-bis].
LOCATOR. The name of a HIP parameter containing zero or more Locator
fields. This parameter's name is distinguished from the Locator
fields embedded within it by the use of all capital letters.
Locator. A name that controls how the packet is routed through the
network and demultiplexed by the end host. It may include a
concatenation of traditional network addresses such as an IPv6
address and end-to-end identifiers such as an ESP SPI. It may
also include transport port numbers or IPv6 Flow Labels as
demultiplexing context, or it may simply be a network address.
Address. A name that denotes a point-of-attachment to the network.
The two most common examples are an IPv4 address and an IPv6
address. The set of possible addresses is a subset of the set of
possible locators.
Preferred locator. A locator on which a host prefers to receive
data. With respect to a given peer, a host always has one active
Preferred locator, unless there are no active locators. By
default, the locators used in the HIP base exchange are the
Preferred locators.
Credit Based Authorization. A host must verify a mobile or
multihomed peer's reachability at a new locator. Credit-Based
Authorization authorizes the peer to receive a certain amount of
data at the new locator before the result of such verification is
known.
3. Protocol Model
This section is an overview; more detailed specification follows this
section.
The overall protocol model is the same as in Section 3 of
[I-D.ietf-hip-rfc5206-bis]; this section only highlights the
differences.
Henderson, et al. Expires January 15, 2013 [Page 4]
Internet-Draft HIP Multihoming July 2012
3.1. Operating Environment
The Host Identity Protocol (HIP) [RFC5201] is a key establishment and
parameter negotiation protocol. Its primary applications are for
authenticating host messages based on host identities, and
establishing security associations (SAs) for the ESP transport format
[RFC5202] and possibly other protocols in the future.
+--------------------+ +--------------------+
| | | |
| +------------+ | | +------------+ |
| | Key | | HIP | | Key | |
| | Management | <-+-----------------------+-> | Management | |
| | Process | | | | Process | |
| +------------+ | | +------------+ |
| ^ | | ^ |
| | | | | |
| v | | v |
| +------------+ | | +------------+ |
| | IPsec | | ESP | | IPsec | |
| | Stack | <-+-----------------------+-> | Stack | |
| | | | | | | |
| +------------+ | | +------------+ |
| | | |
| | | |
| Initiator | | Responder |
+--------------------+ +--------------------+
Figure 1: HIP Deployment Model
The general deployment model for HIP is shown above, assuming
operation in an end-to-end fashion. This document specifies
extensions to the HIP protocol to enable end-host mobility and basic
multihoming. In summary, these extensions to the HIP base protocol
enable the signaling of new addressing information to the peer in HIP
messages. The messages are authenticated via a signature or keyed
hash message authentication code (HMAC) based on its Host Identity.
Henderson, et al. Expires January 15, 2013 [Page 5]
Internet-Draft HIP Multihoming July 2012
---------
| TCP | (sockets bound to HITs)
---------
|
---------
----> | ESP | {HIT_s, HIT_d} <-> SPI
| ---------
| |
---- ---------
| MH |-> | HIP | {HIT_s, HIT_d, SPI} <-> {IP_s, IP_d, SPI}
---- ---------
|
---------
| IP |
---------
Figure 2: Architecture for HIP Multihoming (MH)
Figure 2 depicts a layered architectural view of a HIP-enabled stack
using the ESP transport format. In HIP, upper-layer protocols
(including TCP and ESP in this figure) are bound to Host Identity
Tags (HITs) and not IP addresses. The HIP sublayer is responsible
for maintaining the binding between HITs and IP addresses. The SPI
is used to associate an incoming packet with the right HITs. The
block labeled "MH" is introduced below.
Consider the case when a host is multihomed (has more than one
globally routable address) and has multiple addresses available at
the HIP layer as alternative locators for fault tolerance. Examples
include the use of (possibly multiple) IPv4 and IPv6 addresses on the
same interface, or the use of multiple interfaces attached to
different service providers. Such host multihoming generally
necessitates that a separate ESP SA is maintained for each interface
in order to prevent packets that arrive over different paths from
falling outside of the ESP anti-replay window [RFC4303]. Multihoming
thus makes it possible that the bindings shown on the right side of
Figure 2 are one to many (in the outbound direction, one HIT pair to
multiple SPIs, and possibly then to multiple IP addresses). However,
only one SPI and address pair can be used for any given packet, so
the job of the "MH" block depicted above is to dynamically manipulate
these bindings. Beyond locally managing such multiple bindings, the
peer-to-peer HIP signaling protocol needs to be flexible enough to
define the desired mappings between HITs, SPIs, and addresses, and
needs to ensure that UPDATE messages are sent along the right network
paths so that any HIP-aware middleboxes can observe the SPIs. This
document does not specify the "MH" block, nor does it specify
detailed elements of procedure for how to handle various multihoming
(perhaps combined with mobility) scenarios. The "MH" block may apply
Henderson, et al. Expires January 15, 2013 [Page 6]
Internet-Draft HIP Multihoming July 2012
to more general problems outside of HIP. However, this document does
describe a basic multihoming case (one host adds one address to its
initial address and notifies the peer) and leave more complicated
scenarios for experimentation and future documents.
3.2. Multihoming Overview
In host multihoming, a host has multiple locators simultaneously
rather than sequentially, as in the case of mobility. By using the
LOCATOR parameter defined in [I-D.ietf-hip-rfc5206-bis], a host can
inform its peers of additional (multiple) locators at which it can be
reached, and can declare a particular locator as a "preferred"
locator. Although this document defines a basic mechanism for
multihoming, it does not define detailed policies and procedures,
such as which locators to choose when more than one pair is
available, the operation of simultaneous mobility and multihoming,
source address selection policies (beyond those specified in
[RFC3484]), and the implications of multihoming on transport
protocols and ESP anti-replay windows.
4. Protocol Overview
In this section, we briefly introduce a number of usage scenarios for
HIP multihoming. These scenarios assume that HIP is being used with
the ESP transform [RFC5202], although other scenarios may be defined
in the future. To understand these usage scenarios, the reader
should be at least minimally familiar with the HIP protocol
specification [RFC5201]. However, for the (relatively) uninitiated
reader, it is most important to keep in mind that in HIP the actual
payload traffic is protected with ESP, and that the ESP SPI acts as
an index to the right host-to-host context.
The scenarios below assume that the two hosts have completed a single
HIP base exchange with each other. Both of the hosts therefore have
one incoming and one outgoing SA. Further, each SA uses the same
pair of IP addresses, which are the ones used in the base exchange.
The readdressing protocol is an asymmetric protocol where a mobile or
multihomed host informs a peer host about changes of IP addresses on
affected SPIs. The readdressing exchange is designed to be
piggybacked on existing HIP exchanges. The majority of the packets
on which the LOCATOR parameters are expected to be carried are UPDATE
packets. However, some implementations may want to experiment with
sending LOCATOR parameters also on other packets, such as R1, I2, and
NOTIFY.
The scenarios below at times describe addresses as being in either an
ACTIVE, VERIFIED, or DEPRECATED state. From the perspective of a
Henderson, et al. Expires January 15, 2013 [Page 7]
Internet-Draft HIP Multihoming July 2012
host, newly-learned addresses of the peer must be verified before put
into active service, and addresses removed by the peer are put into a
deprecated state. Under limited conditions described in
[I-D.ietf-hip-rfc5206-bis], an UNVERIFIED address may be used.
Hosts that use link-local addresses as source addresses in their HIP
handshakes may not be reachable by a mobile peer. Such hosts SHOULD
provide a globally routable address either in the initial handshake
or via the LOCATOR parameter.
4.1. Host Multihoming
A (mobile or stationary) host may sometimes have more than one
interface or global address. The host may notify the peer host of
the additional interface or address by using the LOCATOR parameter.
To avoid problems with the ESP anti-replay window, a host SHOULD use
a different SA for each interface or address used to receive packets
from the peer host when multiple locator pairs are being used
simultaneously rather than sequentially.
When more than one locator is provided to the peer host, the host
SHOULD indicate which locator is preferred (the locator on which the
host prefers to receive traffic). By default, the addresses used in
the base exchange are preferred until indicated otherwise.
In the multihoming case, the sender may also have multiple valid
locators from which to source traffic. In practice, a HIP
association in a multihoming configuration may have both a preferred
peer locator and a preferred local locator, although rules for source
address selection should ultimately govern the selection of the
source locator based on the destination locator.
Although the protocol may allow for configurations in which there is
an asymmetric number of SAs between the hosts (e.g., one host has two
interfaces and two inbound SAs, while the peer has one interface and
one inbound SA), it is RECOMMENDED that inbound and outbound SAs be
created pairwise between hosts. When an ESP_INFO arrives to rekey a
particular outbound SA, the corresponding inbound SA should be also
rekeyed at that time. Although asymmetric SA configurations might be
experimented with, their usage may constrain interoperability at this
time. However, it is recommended that implementations attempt to
support peers that prefer to use non-paired SAs. It is expected that
this section and behavior will be modified in future revisions of
this protocol, once the issue and its implications are better
understood.
Consider the case between two hosts, one single-homed and one
multihomed. The multihomed host may decide to inform the single-
Henderson, et al. Expires January 15, 2013 [Page 8]
Internet-Draft HIP Multihoming July 2012
homed host about its other address. It is RECOMMENDED that the
multihomed host set up a new SA pair for use on this new address. To
do this, the multihomed host sends a LOCATOR with an ESP_INFO,
indicating the request for a new SA by setting the OLD SPI value to
zero, and the NEW SPI value to the newly created incoming SPI. A
Locator Type of "1" is used to associate the new address with the new
SPI. The LOCATOR parameter also contains a second Type "1" locator,
that of the original address and SPI. To simplify parameter
processing and avoid explicit protocol extensions to remove locators,
each LOCATOR parameter MUST list all locators in use on a connection
(a complete listing of inbound locators and SPIs for the host). The
multihomed host waits for an ESP_INFO (new outbound SA) from the peer
and an ACK of its own UPDATE. As in the mobility case, the peer host
must perform an address verification before actively using the new
address. Figure 3 illustrates this scenario.
Multi-homed Host Peer Host
UPDATE(ESP_INFO, LOCATOR, SEQ, [DIFFIE_HELLMAN])
----------------------------------->
UPDATE(ESP_INFO, SEQ, ACK, [DIFFIE_HELLMAN,] ECHO_REQUEST)
<-----------------------------------
UPDATE(ACK, ECHO_RESPONSE)
----------------------------------->
Figure 3: Basic Multihoming Scenario
In multihoming scenarios, it is important that hosts receiving
UPDATEs associate them correctly with the destination address used in
the packet carrying the UPDATE. When processing inbound LOCATORs
that establish new security associations on an interface with
multiple addresses, a host uses the destination address of the UPDATE
containing the LOCATOR as the local address to which the LOCATOR plus
ESP_INFO is targeted. This is because hosts may send UPDATEs with
the same (locator) IP address to different peer addresses -- this has
the effect of creating multiple inbound SAs implicitly affiliated
with different peer source addresses.
4.2. Site Multihoming
A host may have an interface that has multiple globally routable IP
addresses. Such a situation may be a result of the site having
multiple upper Internet Service Providers, or just because the site
provides all hosts with both IPv4 and IPv6 addresses. The host
should stay reachable at all or any subset of the currently available
global routable addresses, independent of how they are provided.
This case is handled the same as if there were different IP
Henderson, et al. Expires January 15, 2013 [Page 9]
Internet-Draft HIP Multihoming July 2012
addresses, described above in Section 4.1. Note that a single
interface may experience site multihoming while the host itself may
have multiple interfaces.
Note that a host may be multihomed and mobile simultaneously, and
that a multihomed host may want to protect the location of some of
its interfaces while revealing the real IP address of some others.
This document does not presently specify additional site multihoming
extensions to HIP; further alignment with the IETF shim6 working
group may be considered in the future.
4.3. Dual host multihoming
Consider the case in which both hosts would like to add an additional
address after the base exchange completes. In Figure 4, consider
that host1, which used address addr1a in the base exchange to set up
SPI1a and SPI2a, wants to add address addr1b. It would send an
UPDATE with LOCATOR (containing the address addr1b) to host2, using
destination address addr2a, and a new set of SPIs would be added
between hosts 1 and 2 (call them SPI1b and SPI2b -- not shown in the
figure). Next, consider host2 deciding to add addr2b to the
relationship. Host2 must select one of host1's addresses towards
which to initiate an UPDATE. It may choose to initiate an UPDATE to
addr1a, addr1b, or both. If it chooses to send to both, then a full
mesh (four SA pairs) of SAs would exist between the two hosts. This
is the most general case; it often may be the case that hosts
primarily establish new SAs only with the peer's Preferred locator.
The readdressing protocol is flexible enough to accommodate this
choice.
-<- SPI1a -- -- SPI2a ->-
host1 < > addr1a <---> addr2a < > host2
->- SPI2a -- -- SPI1a -<-
addr1b <---> addr2a (second SA pair)
addr1a <---> addr2b (third SA pair)
addr1b <---> addr2b (fourth SA pair)
Figure 4: Dual Multihoming Case in Which Each Host Uses LOCATOR to
Add a Second Address
4.4. Combined Mobility and Multihoming
It looks likely that in the future, many mobile hosts will be
simultaneously mobile and multihomed, i.e., have multiple mobile
interfaces. Furthermore, if the interfaces use different access
technologies, it is fairly likely that one of the interfaces may
Henderson, et al. Expires January 15, 2013 [Page 10]
Internet-Draft HIP Multihoming July 2012
appear stable (retain its current IP address) while some other(s) may
experience mobility (undergo IP address change).
The use of LOCATOR plus ESP_INFO should be flexible enough to handle
most such scenarios, although more complicated scenarios have not
been studied so far.
4.5. Initiating the Protocol in R1 or I2
A Responder host MAY include a LOCATOR parameter in the R1 packet
that it sends to the Initiator. This parameter MUST be protected by
the R1 signature. If the R1 packet contains LOCATOR parameters with
a new Preferred locator, the Initiator SHOULD directly set the new
Preferred locator to status ACTIVE without performing address
verification first, and MUST send the I2 packet to the new Preferred
locator. The I1 destination address and the new Preferred locator
may be identical. All new non-preferred locators must still undergo
address verification once the base exchange completes.
Initiator Responder
R1 with LOCATOR
<-----------------------------------
record additional addresses
change responder address
I2 sent to newly indicated preferred address
----------------------------------->
(process normally)
R2
<-----------------------------------
(process normally, later verification of non-preferred locators)
Figure 5: LOCATOR Inclusion in R1
An Initiator MAY include one or more LOCATOR parameters in the I2
packet, independent of whether or not there was a LOCATOR parameter
in the R1. These parameters MUST be protected by the I2 signature.
Even if the I2 packet contains LOCATOR parameters, the Responder MUST
still send the R2 packet to the source address of the I2. The new
Preferred locator SHOULD be identical to the I2 source address. If
the I2 packet contains LOCATOR parameters, all new locators must
undergo address verification as usual, and the ESP traffic that
subsequently follows should use the Preferred locator.
Henderson, et al. Expires January 15, 2013 [Page 11]
Internet-Draft HIP Multihoming July 2012
Initiator Responder
I2 with LOCATOR
----------------------------------->
(process normally)
record additional addresses
R2 sent to source address of I2
<-----------------------------------
(process normally)
Figure 6: LOCATOR Inclusion in I2
The I1 and I2 may be arriving from different source addresses if the
LOCATOR parameter is present in R1. In this case, implementations
simultaneously using multiple pre-created R1s, indexed by Initiator
IP addresses, may inadvertently fail the puzzle solution of I2
packets due to a perceived puzzle mismatch. See, for instance, the
example in Appendix A of [RFC5201]. As a solution, the Responder's
puzzle indexing mechanism must be flexible enough to accommodate the
situation when R1 includes a LOCATOR parameter.
5. Other Considerations
5.1. Address Verification
An address verification method is specified in
[I-D.ietf-hip-rfc5206-bis]. It is expected that addresses learned in
multihoming scenarios also are subject to the same verification
rules.
5.2. Preferred Locator
When a host has multiple locators, the peer host must decide which to
use for outbound packets. It may be that a host would prefer to
receive data on a particular inbound interface. HIP allows a
particular locator to be designated as a Preferred locator and
communicated to the peer.
In general, when multiple locators are used for a session, there is
the question of using multiple locators for failover only or for
load-balancing. Due to the implications of load-balancing on the
transport layer that still need to be worked out, this document
assumes that multiple locators are used primarily for failover. An
implementation may use ICMP interactions, reachability checks, or
other means to detect the failure of a locator.
Henderson, et al. Expires January 15, 2013 [Page 12]
Internet-Draft HIP Multihoming July 2012
5.3. Interaction with Security Associations
This document uses the HIP LOCATOR protocol parameter, specified in
[I-D.ietf-hip-rfc5206-bis]), that allows the hosts to exchange
information about their locator(s) and any changes in their
locator(s). The logical structure created with LOCATOR parameters
has three levels: hosts, Security Associations (SAs) indexed by
Security Parameter Indices (SPIs), and addresses.
The relation between these levels for an association constructed as
defined in the base specification [RFC5201] and ESP transform
[RFC5202] is illustrated in Figure 7.
-<- SPI1a -- -- SPI2a ->-
host1 < > addr1a <---> addr2a < > host2
->- SPI2a -- -- SPI1a -<-
Figure 7: Relation between Hosts, SPIs, and Addresses (Base
Specification)
In Figure 7, host1 and host2 negotiate two unidirectional SAs, and
each host selects the SPI value for its inbound SA. The addresses
addr1a and addr2a are the source addresses that the hosts use in the
base HIP exchange. These are the "preferred" (and only) addresses
conveyed to the peer for use on each SA. That is, although packets
sent to any of the hosts' interfaces may be accepted on the inbound
SA, the peer host in general knows of only the single destination
address learned in the base exchange (e.g., for host1, it sends a
packet on SPI2a to addr2a to reach host2), unless other mechanisms
exist to learn of new addresses.
In general, the bindings that exist in an implementation
corresponding to this document can be depicted as shown in Figure 8.
In this figure, a host can have multiple inbound SPIs (and, not
shown, multiple outbound SPIs) associated with another host.
Furthermore, each SPI may have multiple addresses associated with it.
These addresses that are bound to an SPI are not used to lookup the
incoming SA. Rather, the addresses are those that are provided to
the peer host, as hints for which addresses to use to reach the host
on that SPI. The LOCATOR parameter is used to change the set of
addresses that a peer associates with a particular SPI.
Henderson, et al. Expires January 15, 2013 [Page 13]
Internet-Draft HIP Multihoming July 2012
address11
/
SPI1 - address12
/
/ address21
host -- SPI2 <
\ address22
\
SPI3 - address31
\
address32
Figure 8: Relation between Hosts, SPIs, and Addresses (General Case)
A host may establish any number of security associations (or SPIs)
with a peer. The main purpose of having multiple SPIs with a peer is
to group the addresses into collections that are likely to experience
fate sharing. For example, if the host needs to change its addresses
on SPI2, it is likely that both address21 and address22 will
simultaneously become obsolete. In a typical case, such SPIs may
correspond with physical interfaces; see below. Note, however, that
especially in the case of site multihoming, one of the addresses may
become unreachable while the other one still works. In the typical
case, however, this does not require the host to inform its peers
about the situation, since even the non-working address still
logically exists.
A basic property of HIP SAs is that the inbound IP address is not
used to lookup the incoming SA. Therefore, in Figure 8, it may seem
unnecessary for address31, for example, to be associated only with
SPI3 -- in practice, a packet may arrive to SPI1 via destination
address address31 as well. However, the use of different source and
destination addresses typically leads to different paths, with
different latencies in the network, and if packets were to arrive via
an arbitrary destination IP address (or path) for a given SPI, the
reordering due to different latencies may cause some packets to fall
outside of the ESP anti-replay window. For this reason, HIP provides
a mechanism to affiliate destination addresses with inbound SPIs,
when there is a concern that anti-replay windows might be violated.
In this sense, we can say that a given inbound SPI has an "affinity"
for certain inbound IP addresses, and this affinity is communicated
to the peer host. Each physical interface SHOULD have a separate SA,
unless the ESP anti-replay window is loose.
Moreover, even when the destination addresses used for a particular
SPI are held constant, the use of different source interfaces may
also cause packets to fall outside of the ESP anti-replay window,
since the path traversed is often affected by the source address or
Henderson, et al. Expires January 15, 2013 [Page 14]
Internet-Draft HIP Multihoming July 2012
interface used. A host has no way to influence the source interface
on which a peer sends its packets on a given SPI. A host SHOULD
consistently use the same source interface and address when sending
to a particular destination IP address and SPI. For this reason, a
host may find it useful to change its SPI or at least reset its ESP
anti-replay window when the peer host readdresses.
An address may appear on more than one SPI. This creates no
ambiguity since the receiver will ignore the IP addresses during SA
lookup anyway. However, this document does not specify such cases.
When the LOCATOR parameter is sent in an UPDATE packet, then the
receiver will respond with an UPDATE acknowledgment. When the
LOCATOR parameter is sent in an R1 or I2 packet, the base exchange
retransmission mechanism will confirm its successful delivery.
LOCATORs may experimentally be used in NOTIFY packets; in this case,
the recipient MUST consider the LOCATOR as informational and not
immediately change the current preferred address, but can test the
additional locators when the need arises. The use of the LOCATOR in
a NOTIFY message may not be compatible with middleboxes.
6. Processing Rules
Processing rules are specified in [I-D.ietf-hip-rfc5206-bis]. Future
versions of this document will specify multihoming-specific
processing rules here.
6.1. Sending LOCATORs
The decision of when to send LOCATORs is basically a local policy
issue. However, it is RECOMMENDED that a host send a LOCATOR
whenever it recognizes a change of its IP addresses in use on an
active HIP association, and assumes that the change is going to last
at least for a few seconds. Rapidly sending LOCATORs that force the
peer to change the preferred address SHOULD be avoided.
When a host decides to inform its peers about changes in its IP
addresses, it has to decide how to group the various addresses with
SPIs. The grouping should consider also whether middlebox
interaction requires sending the same LOCATOR in separate UPDATEs on
different paths. Since each SPI is associated with a different
Security Association, the grouping policy may also be based on ESP
anti-replay protection considerations. In the typical case, simply
basing the grouping on actual kernel level physical and logical
interfaces may be the best policy. Grouping policy is outside of the
scope of this document.
Note that the purpose of announcing IP addresses in a LOCATOR is to
Henderson, et al. Expires January 15, 2013 [Page 15]
Internet-Draft HIP Multihoming July 2012
provide connectivity between the communicating hosts. In most cases,
tunnels or virtual interfaces such as IPsec tunnel interfaces or
Mobile IP home addresses provide sub-optimal connectivity.
Furthermore, it should be possible to replace most tunnels with HIP
based "non-tunneling", therefore making most virtual interfaces
fairly unnecessary in the future. Therefore, virtual interfaces
SHOULD NOT be announced in general. On the other hand, there are
clearly situations where tunnels are used for diagnostic and/or
testing purposes. In such and other similar cases announcing the IP
addresses of virtual interfaces may be appropriate.
Hosts MUST NOT announce broadcast or multicast addresses in LOCATORs.
Link-local addresses MAY be announced to peers that are known to be
neighbors on the same link, such as when the IP destination address
of a peer is also link-local. The announcement of link-local
addresses in this case is a policy decision; link-local addresses
used as Preferred locators will create reachability problems when the
host moves to another link. In any case, link-local addresses MUST
NOT be announced to a peer unless that peer is known to be on the
same link.
Once the host has decided on the groups and assignment of addresses
to the SPIs, it creates a LOCATOR parameter that serves as a complete
representation of the addresses and affiliated SPIs intended for
active use. We now describe a few cases introduced in Section 4. We
assume that the Traffic Type for each locator is set to "0" (other
values for Traffic Type may be specified in documents that separate
the HIP control plane from data plane traffic). Other mobility and
multihoming cases are possible but are left for further
experimentation.
1. Host multihoming (addition of an address). We only describe the
simple case of adding an additional address to a (previously)
single-homed, non-mobile host. The host SHOULD set up a new SA
pair between this new address and the preferred address of the
peer host. To do this, the multihomed host creates a new inbound
SA and creates a new SPI. For the outgoing UPDATE message, it
inserts an ESP_INFO parameter with an OLD SPI field of "0", a NEW
SPI field corresponding to the new SPI, and a KEYMAT Index as
selected by local policy. The host adds to the UPDATE message a
LOCATOR with two Type "1" Locators: the original address and SPI
active on the association, and the new address and new SPI being
added (with the SPI matching the NEW SPI contained in the
ESP_INFO). The Preferred bit SHOULD be set depending on the
policy to tell the peer host which of the two locators is
preferred. The UPDATE also contains a SEQ parameter and
optionally a DIFFIE_HELLMAN parameter, and follows rekeying
procedures with respect to this new address. The UPDATE message
Henderson, et al. Expires January 15, 2013 [Page 16]
Internet-Draft HIP Multihoming July 2012
SHOULD be sent to the peer's Preferred address with a source
address corresponding to the new locator.
The sending of multiple LOCATORs, locators with Locator Type "0", and
multiple ESP_INFO parameters is for further study. Note that the
inclusion of LOCATOR in an R1 packet requires the use of Type "0"
locators since no SAs are set up at that point.
6.2. Handling Received LOCATORs
A host SHOULD be prepared to receive a LOCATOR parameter in the
following HIP packets: R1, I2, UPDATE, and NOTIFY.
This document describes sending both ESP_INFO and LOCATOR parameters
in an UPDATE. The ESP_INFO parameter is included when there is a
need to rekey or key a new SPI, and is otherwise included for the
possible benefit of HIP-aware middleboxes. The LOCATOR parameter
contains a complete map of the locators that the host wishes to make
or keep active for the HIP association.
In general, the processing of a LOCATOR depends upon the packet type
in which it is included. Here, we describe only the case in which
ESP_INFO is present and a single LOCATOR and ESP_INFO are sent in an
UPDATE message; other cases are for further study. The steps below
cover each of the cases described in Section 6.1.
The processing of ESP_INFO and LOCATOR parameters is intended to be
modular and support future generalization to the inclusion of
multiple ESP_INFO and/or multiple LOCATOR parameters. A host SHOULD
first process the ESP_INFO before the LOCATOR, since the ESP_INFO may
contain a new SPI value mapped to an existing SPI, while a Type "1"
locator will only contain a reference to the new SPI.
When a host receives a validated HIP UPDATE with a LOCATOR and
ESP_INFO parameter, it processes the ESP_INFO as follows. The
ESP_INFO parameter indicates whether an SA is being rekeyed, created,
deprecated, or just identified for the benefit of middleboxes. The
host examines the OLD SPI and NEW SPI values in the ESP_INFO
parameter:
1. (no rekeying) If the OLD SPI is equal to the NEW SPI and both
correspond to an existing SPI, the ESP_INFO is gratuitous
(provided for middleboxes) and no rekeying is necessary.
2. (rekeying) If the OLD SPI indicates an existing SPI and the NEW
SPI is a different non-zero value, the existing SA is being
rekeyed and the host follows HIP ESP rekeying procedures by
creating a new outbound SA with an SPI corresponding to the NEW
Henderson, et al. Expires January 15, 2013 [Page 17]
Internet-Draft HIP Multihoming July 2012
SPI, with no addresses bound to this SPI. Note that locators in
the LOCATOR parameter will reference this new SPI instead of the
old SPI.
3. (new SA) If the OLD SPI value is zero and the NEW SPI is a new
non-zero value, then a new SA is being requested by the peer.
This case is also treated like a rekeying event; the receiving
host must create a new SA and respond with an UPDATE ACK.
4. (deprecating the SA) If the OLD SPI indicates an existing SPI and
the NEW SPI is zero, the SA is being deprecated and all locators
uniquely bound to the SPI are put into the DEPRECATED state.
If none of the above cases apply, a protocol error has occurred and
the processing of the UPDATE is stopped.
Next, the locators in the LOCATOR parameter are processed. For each
locator listed in the LOCATOR parameter, check that the address
therein is a legal unicast or anycast address. That is, the address
MUST NOT be a broadcast or multicast address. Note that some
implementations MAY accept addresses that indicate the local host,
since it may be allowed that the host runs HIP with itself.
The below assumes that all locators are of Type "1" with a Traffic
Type of "0"; other cases are for further study.
For each Type "1" address listed in the LOCATOR parameter, the host
checks whether the address is already bound to the SPI indicated. If
the address is already bound, its lifetime is updated. If the status
of the address is DEPRECATED, the status is changed to UNVERIFIED.
If the address is not already bound, the address is added, and its
status is set to UNVERIFIED. Mark all addresses corresponding to the
SPI that were NOT listed in the LOCATOR parameter as DEPRECATED.
As a result, at the end of processing, the addresses listed in the
LOCATOR parameter have either a state of UNVERIFIED or ACTIVE, and
any old addresses on the old SA not listed in the LOCATOR parameter
have a state of DEPRECATED.
Once the host has processed the locators, if the LOCATOR parameter
contains a new Preferred locator, the host SHOULD initiate a change
of the Preferred locator. This requires that the host first verifies
reachability of the associated address, and only then changes the
Preferred locator; see Section 6.4.
If a host receives a locator with an unsupported Locator Type, and
when such a locator is also declared to be the Preferred locator for
the peer, the host SHOULD send a NOTIFY error with a Notify Message
Henderson, et al. Expires January 15, 2013 [Page 18]
Internet-Draft HIP Multihoming July 2012
Type of LOCATOR_TYPE_UNSUPPORTED, with the Notification Data field
containing the locator(s) that the receiver failed to process.
Otherwise, a host MAY send a NOTIFY error if a (non-preferred)
locator with an unsupported Locator Type is received in a LOCATOR
parameter.
6.3. Verifying Address Reachability
Address verification is defined in [I-D.ietf-hip-rfc5206-bis].
When address verification is in progress for a new Preferred locator,
the host SHOULD select a different locator listed as ACTIVE, if one
such locator is available, to continue communications until address
verification completes. Alternatively, the host MAY use the new
Preferred locator while in UNVERIFIED status to the extent Credit-
Based Authorization permits. Credit-Based Authorization is explained
in [I-D.ietf-hip-rfc5206-bis]. Once address verification succeeds,
the status of the new Preferred locator changes to ACTIVE.
6.4. Changing the Preferred Locator
A host MAY want to change the Preferred outgoing locator for
different reasons, e.g., because traffic information or ICMP error
messages indicate that the currently used preferred address may have
become unreachable. Another reason may be due to receiving a LOCATOR
parameter that has the "P" bit set.
To change the Preferred locator, the host initiates the following
procedure:
1. If the new Preferred locator has ACTIVE status, the Preferred
locator is changed and the procedure succeeds.
2. If the new Preferred locator has UNVERIFIED status, the host
starts to verify its reachability. The host SHOULD use a
different locator listed as ACTIVE until address verification
completes if one such locator is available. Alternatively, the
host MAY use the new Preferred locator, even though in UNVERIFIED
status, to the extent Credit-Based Authorization permits. Once
address verification succeeds, the status of the new Preferred
locator changes to ACTIVE and its use is no longer governed by
Credit-Based Authorization.
3. If the peer host has not indicated a preference for any address,
then the host picks one of the peer's ACTIVE addresses randomly
or according to policy. This case may arise if, for example,
ICMP error messages that deprecate the Preferred locator arrive,
but the peer has not yet indicated a new Preferred locator.
Henderson, et al. Expires January 15, 2013 [Page 19]
Internet-Draft HIP Multihoming July 2012
4. If the new Preferred locator has DEPRECATED status and there is
at least one non-deprecated address, the host selects one of the
non-deprecated addresses as a new Preferred locator and
continues. If the selected address is UNVERIFIED, the address
verification procedure described above will apply.
7. Security Considerations
Security considerations are addressed in [I-D.ietf-hip-rfc5206-bis].
8. IANA Considerations
None.
9. Authors and Acknowledgments
This document contains content that was originally included in
RFC5206. Pekka Nikander and Jari Arkko originated RFC5206, and
Christian Vogt and Thomas Henderson (editor) later joined as co-
authors. Also in RFC5206, Greg Perkins contributed the initial draft
of the security section, and Petri Jokela was a co-author of the
initial individual submission.
The authors thank Miika Komu, Mika Kousa, Jeff Ahrenholz, and Jan
Melen for many improvements to the document.
10. References
10.1. Normative references
[I-D.ietf-hip-rfc5206-bis] Nikander, P., Henderson, T., Vogt, C.,
and J. Arkko, "End-Host Mobility and
Multihoming with the Host Identity
Protocol", draft-ietf-hip-rfc5206-bis-00
(work in progress), August 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs
to Indicate Requirement Levels", BCP 14,
RFC 2119, March 1997.
[RFC3484] Draves, R., "Default Address Selection
for Internet Protocol version 6 (IPv6)",
RFC 3484, February 2003.
[RFC4303] Kent, S., "IP Encapsulating Security
Payload (ESP)", RFC 4303, December 2005.
[RFC4423] Moskowitz, R. and P. Nikander, "Host
Henderson, et al. Expires January 15, 2013 [Page 20]
Internet-Draft HIP Multihoming July 2012
Identity Protocol (HIP) Architecture",
RFC 4423, May 2006.
[RFC5201] Moskowitz, R., Nikander, P., Jokela, P.,
and T. Henderson, "Host Identity
Protocol", RFC 5201, April 2008.
[RFC5202] Jokela, P., Moskowitz, R., and P.
Nikander, "Using the Encapsulating
Security Payload (ESP) Transport Format
with the Host Identity Protocol (HIP)",
RFC 5202, April 2008.
10.2. Informative references
[RFC5204] Laganier, J. and L. Eggert, "Host
Identity Protocol (HIP) Rendezvous
Extension", RFC 5204, April 2008.
[RFC5533] Nordmark, E. and M. Bagnulo, "Shim6:
Level 3 Multihoming Shim Protocol for
IPv6", RFC 5533, June 2009.
Appendix A. Document Revision History
To be removed upon publication
+----------+--------------------------------------------------------+
| Revision | Comments |
+----------+--------------------------------------------------------+
| draft-00 | Initial version with multihoming text imported from |
| | RFC5206. |
+----------+--------------------------------------------------------+
Authors' Addresses
Thomas R. Henderson (editor)
The Boeing Company
P.O. Box 3707
Seattle, WA
USA
EMail: thomas.r.henderson@boeing.com
Henderson, et al. Expires January 15, 2013 [Page 21]
Internet-Draft HIP Multihoming July 2012
Christian Vogt
Ericsson Research NomadicLab
Hirsalantie 11
JORVAS FIN-02420
FINLAND
Phone:
EMail: christian.vogt@ericsson.com
Jari Arkko
Ericsson Research NomadicLab
JORVAS FIN-02420
FINLAND
Phone: +358 40 5079256
EMail: jari.arkko@ericsson.com
Henderson, et al. Expires January 15, 2013 [Page 22]