subnet prefix length > 64 breaks IPv6?

Glen Kent glen.kent at
Wed Dec 28 16:36:19 UTC 2011

> So a typical forwarding step is already a two step process:
>  Look up variable length prefix to get next hop.
>  Look up 128 bit next hop to get forwarding information.


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.  AFAIK, in all recent products
> this is how all vendors handle the problem (at a high level).

You only use the TCAM for #1, not for #2.


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