WG Review: Site Multihoming by IPv6 Intermediation (shim6)

IESG <iesg@ietf.org> Mon, 20 June 2005 14:53 UTC

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Subject: WG Review: Site Multihoming by IPv6 Intermediation (shim6)
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A new IETF working group has been proposed in the Internet Area. The IESG has
not made any determination as yet. The following draft charter was submitted,
and is provided for informational purposes only. Please send your comments to
the IESG mailing list (iesg@ietf.org) by Friday, June 24th. 


Site Multihoming by IPv6 Intermediation (shim6)

Current Status: Proposed Working Group 

Internet Area Director(s):
Mark Townsley <townsley at cisco.com>
Margaret Wasserman <margaret at thingmagic.com>

Internet Area Advisor:

WG Chair(s):

Technical Advisor(s):


Mailing List: shim6 at psg.com
To Subscribe: shim6-request at psg.com
Archive: TBD


For the purposes of redundancy, load sharing, operational policy or cost, a
site may be multi-homed, with the site's network having connections to
multiple IP service providers. The current Internet routing infrastructure
permits multi-homing using provider independent addressing, and adapts to
changes in the availability of these connections. However if the site uses
multiple provider-assigned address prefixes for every host within the site,
host application associations cannot use alternate paths, such as for
surviving the changes or for creating new associations, when one or more of
the site's address prefixes becomes unreachable. This working group will
produce specifications for an IPv6-based site multi-homing solution that
inserts a new sub-layer (shim) into the IP stack of end-system hosts. It
will enable hosts on multi-homed sites to use a set of provider-assigned IP
address prefixes and switch between them without upsetting transport
protocols or applications.

The work will be based on the architecture developed by the IETF multi6
working group. The shim6 working group is to complete the required protocol
developments and the architecture and security analysis of the required

Requirements for the solution are:

o The approach must handle re-homing both existing communication and
being able to establish new communication when one or more of the
addresses is unreachable.

o IPv6 NAT devices are assumed not to exist, or not to present an
obstacle about which the shim6 solution needs to be concerned.

o Only IPv6 is considered.

o Changes in the addresses that are used below the shim will be invisible
to the upper layers, which will see a fixed address (termed Upper Layer
Identifier or ULID).

o ULIDs will be actual IP addresses, permitting existing applications to
continue to work unchanged, and permitting application referrals to
work, as long as the IP Addresses are available.

o The solution should assume ingress filtering may be applied at network

o The solution must allow the global routing system to scale even if there
is a very large number of multi-homed sites. This implies that re-homing
not be visible to the routing system.

o Compatibility will remain for existing mobility mechanisms. It will
be possible to use Mobile IPv6 on a node that also supports Shim6.
However, any optimizations or advanced configurations are out of
scope for shim6.

o The approach is to provide an optimized way to handle a static set of
addresses, while also providing a way to securely handle dynamic
changes in the set of addresses. The dynamic changes might be useful
for future combinations of multi-homing and IP mobility, but the working
group will not take on such mobility capabilities directly.

o The specifications must specifically refer to all applicable threats and
describe how they are handled, with the requirement being that the
resulting solution not introduce any threats that make the security any
less than in today's Internet.

The background documents to be considered by the WG include:

RFC 3582

The input documents that the WG will use as the basis for its design are:


In addition to the network layer shim solution, the shim6 WG is
specifically chartered to work on:

o Solutions for site exit router selection that work when each ISP
uses ingress filtering, i.e. when the chosen site exit needs to
be related to the source address chosen by the host. This site
exit router selection and the associated address selection
process should work whether or not the peer site supports
the shim6 protocol.

o Solutions to establish new communications after an outage has
occurred that do not require shim support from the
non-multihomed end of the communication. The Working Group will
explore whether such solutions are also useful when both ends
support the shim.

o The possible impact of the use of multiple locators at both ends
on congestion control, traffic engineering, and QoS will be analysed
in conjunction with the Transport Area.

o The relationships between Upper Layer Identifiers (ULIDs)
and unique local addresses.

o ICMP error demuxing for locator failure discovery.

o If necessary, develop and specify formats and structure for:

- Cryptographically protected locators
- Carrying the flow label across the shim layer
defined in the multi6 architecture.

The shim6 WG is to publish, as standards track RFC's, specifications with
enough details to allow fully interoperable implementations.


AUG 05 First draft of architectural document
AUG 05 First draft of protocol document
AUG 05 First draft on cryptographic locators, if required
AUG 05 First draft on multi-homing triggers description
AUG 05 First draft on applicability statement document
OCT 05 WG last-call on architectural document
OCT 05 WG last-call on applicability statement document
FEB 06 WG last-call on protocol document
FEB 06 WG last-call on cryptographic locators, if required
FEB 06 Submit completed architectural document to IESG
FEB 06 Submit applicability statement document to IESG
APR 06 WG last-call on multihoming triggers description
APR 06 Submit document on cryptographic locators to the IESG, if
APR 06 Submit protocol document to the IESG
JUN 06 Submit draft on multihoming triggers description to the IESG

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