Subject: Thoughts on a DHCPv6 option to enable CPE router processing of ICMP Redirects ?

From: Mark Smith <[email-masked]>
Date: Sun, 24 Jun 2007 20:16:29 +0930

Hi,

I've been thinking about how IPv6 might be deployed in a DSL network
with Ethernet rather than ATM backhaul. The IPv6 traffic rides directly
over Ethernet - the so-called "IPoE" DSL model - rather than being
encapsulated in PPPoE or PPPoA.

In this scenario, customers would be allocated a /48 (or longer)
prefixes for their network, sitting behind the DSL CPE operating as a
router, via DHCP Prefix Delegation.

At the local exchange/central office, the bridged-ethernet-over-DSL
traffic is aggregated from the DSLAMs using a layer 2 switch. This
layer 2 switch aggregated traffic is then backhauled, also via
ethernet, to a central aggregation point where the aggregation router
resides, which provides access to the rest of the IPv6 Internet.

Ideally, traffic between the prefixes goes between the CPE directly via
the layer 2 switch in the exchange/co, rather than via the upstream
aggregation router. However, as the CPE only has a default route to the
upstream aggregation router this isn't going to happen.

In the "convetional" routing scenario, the CPE router and the
aggregation router would be participating in a routing protocol, and
therefore the CPE would know about the prefixes residing behind the
other peer CPE. In this DSL scenario this isn't scalable or
manageble. 

I'm curious on what people's thoughts would be regarding having a DHCP
option that enables the CPE router process ICMP redirects for these
prefixes from the upstream aggregation router? This would encourage
most inter-cpe prefix traffic to stay local to the exchange/c.o.,
without having to run a fully blown routing protocol on each of them.
With increasing P2P style applications and therefore traffic, I think
there would be real benefits in permitting ICMP redirects be processed
by the CPE routers in this scenario.

Regards,
Mark.

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From: Mark Smith <[email-masked]>
Date: Sun, 24 Jun 2007 22:42:34 +0930

Hmm,

On Sun, 24 Jun 2007 20:16:29 +0930

> Hi,

<snip>
 
> by the CPE routers in this scenario.

Hmm, I've just realised that conventional ICMP redirect won't work in
this scenario, because the target address of the ICMP redirect couldn't
be the downstream CPE, as the upstream aggregation router wouldn't know
what the Link Local address of the CPE is from the packet that
triggered the redirect.

OTOH, maybe the IPv6 destination address of the ICMP redirect could be
the subnet router-anycast address, and use the link layer destination
address that was the link layer source address of the packet that
triggered the redirect.

Regards,
Mark.