Subject: (ngtrans) 6to4 gateway / 6to4 relay router IPv4-compatible IPv6 address interoperability concern ...

From: "John Spence" <[email-masked]>
Date: Thu, 7 Jun 2001 12:12:25 -0700

We've recently implemented a production 6to4 relay router to carry
transit packets to/from the 6to4 environment to/from native IPv6
networks.  We've built our implementation on Cisco.

During testing, we discovered what may be an implementation-specific
problem with the 6to4 spec.  Specifically, Microsoft's
implementation of a 6to4 gateway (6to4 client software) uses an
echo-request test to the relay's IPv4-compatible IPv6 address to
verify that the relay is reachable.  Cisco's 6to4 pseudo-interface
implementation does not automatically configure an IPv4-compatible
IPv6 address on the router's 6to4 interface, nor do the current
versions of IPv6-enabled IOS allow you to manually configure the
IPv4-compatible IPv6 address on that logical or physical interface.
We were able to configure a second "auto-tunnel" pseudo-interface
that responds to the IPv4-compatible IPv6 echo-request as a
workaround. Only after that workaround was in place would the
(Microsoft IPv6 Technology Preview for Windows 2000) 6to4cfg.exe
"ping test" be successful, and configure our Cisco relay router.

In this case, it appears both vendors have correctly implemented the
6to4 specifications, but yielded an environment that does not
interoperate cleanly.

Good to have an operational workaround. Still, perhaps it would be
good to include in the 6to4 spec a statement that "the relay router
MUST configure the 6to4 pseudo-interface with the appropriate
IPv4-compatible IPv6 address".  In the interim before a better
relay-router-selection mechanism is available (see
draft-ietf-ngtrans-6to4anycast-03.txt), many 6to4 router providers
are likely to do some relay-verification before configuring a
specified (or default) relay.  This should improve interoperability
between 6to4 gateways and 6to4 relay routers in the mixed-vendor
environment expected.

Has anyone else encountered this situation, and can add other
insight?

John Spence and Brian Skeen
---------------------------------------
John E Spence ZAMA NETWORKS
IT Manager/Senior Systems Engineer
[email-masked] | www.zama.net
wk 206.835.5316 cell 206.571.9792
---------------------------------------

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From: Brian E Carpenter <[email-masked]>
Date: Sat, 09 Jun 2001 08:12:02 -0500

John,

The echo-request test you refer to seems to be an implementor's
addition to the spec; it is not required by RFC 3056.

Personally I don't quite understand why the implementation
you mention uses the relay's IPv4-compatible IPv6 address for an
echo-request; that has nothing whatever to do with 6to4. Even if it
answers, that doesn't tell you there is a 6to4 relay in the same box.

I would have expected any echo-request to be sent to the relay's 
2002:: address, which is the IPv6 next-hop address used to send 6to4 
packets to the relay, and is by definition configured at the relay. 
However, since the echo-request is not part of RFC 3056, and the IPv4-
compatible address is in a separate universe, I don't see why
we need to change the spec. 

   Brian