[147949] in North American Network Operators' Group
Re: subnet prefix length > 64 breaks IPv6?
daemon@ATHENA.MIT.EDU (Glen Kent)
Wed Dec 28 11:37:13 2011
In-Reply-To: <20111228155712.GB59760@ussenterprise.ufp.org>
Date: Wed, 28 Dec 2011 22:06:19 +0530
From: Glen Kent <glen.kent@gmail.com>
To: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
>
> So a typical forwarding step is already a two step process:
>
> =A0Look up variable length prefix to get next hop.
> =A0Look up 128 bit next hop to get forwarding information.
Wrong.
You only do a lookup once.
You look up a TCAM or a hash table that gives you the next hop for a route.
You DONT need to do another TCAM lookup to get the egress
encapsulation information.
You get the egress encapsulation after your TCAM lookup. It typically
gives you an index that stores this information. All routes pointing
to one nexthop will typically point to the same index.
> Once the vendor has built a 128-bit TCAM for step #2, there's no
> reason not to use it for step #1 as well. =A0AFAIK, in all recent product=
s
> this is how all vendors handle the problem (at a high level).
You only use the TCAM for #1, not for #2.
Glen
