subnet prefix length > 64 breaks IPv6?

Ryan Malayter malayter at
Wed Dec 28 14:35:11 UTC 2011

On Dec 28, 7:10 am, sth... at wrote:
> > On the other hand there's also the rule that IPv6 is classless and therefore routing on any prefix length must be supported, although for some implementations forwarding based on > /64 is somewhat less efficient.
> Can you please name names for the "somewhat less efficient" part? I've
> seen this and similar claims several times, but the lack of specific
> information is rather astounding.

Well, I do know if you look at the specs for most newer L3 switches,
they will often say something like "max IPv4 routes 8192, max IPv6
routes 4096". This leads one to believe that the TCAMs/hash tables are
only using 64 bits for IPv6 forwarding, and therefores longer prefixes
must be handled in software.

This may very well not be true "under the hood" at all, but the fact
that vendors publish so little IPv6 specification and benchmarking
information doesn't help matters.

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