RE: The state of IPv6 multihoming development

["Craig A. Huegen" <chuegen@cisco.com>]

On Sat, 26 Oct 2002, Tony Hain wrote:

> I know Craig said the host is making a routing decision, but it isn't.
> Even if it tried it could be overruled by the routers for the outbound
> packets. The only thing the host can decide that might even come close
> to a routing decision is the address that the remote node will use to
> talk back toward it. This is not a routing decision, but for those who
> are into fine-grained TE, it might be considered a policy decision.

There's a significant difference between being able to override normal
path selection via significant manual policy configuration and performing
path selection as a normal path of course.

As an example, www.cisco.com may have addresses of 2001:420:9c3b:1::2 and
2003:602:b1cd:1::2.

client.example.com selects 2001:420:9c3b:1::2.  example.com's routing
infrastructure doesn't know of the alternate path (if 2003:602:b1cd:1::2
were used as the destination IP address). Sure, example.com *could* put in
a policy to look for packets to 2001:420:9c3b::/48 and force it down a
different path, but it's completely manual and example.com's border has
absolutely no visibility of this.  Instead, example.com is most likely to
hand the packets for 2001:420:9c3b::/48 to its best path to 2001:420::/32,
the provider aggregate, unless manually overridden.  The infrastructure
has no way to evaluate an alternate path.

What's most important here is that the routing infrastructure has
absolutely no visibility that the destination 2001:420:9c3b:1::2 has an
alternate path, to the address 2003:602:b1cd:1::2.

/cah

---
Craig A. Huegen, Chief Network Architect      C i s c o  S y s t e m s
IT Transport, Network Technology & Design           ||        ||
Cisco Systems, Inc., 400 East Tasman Drive          ||        ||
San Jose, CA  95134, (408) 526-8104                ||||      ||||
email: chuegen@cisco.com       CCIE #2100      ..:||||||:..:||||||:..