subnet prefix length > 64 breaks IPv6?

Glen Kent glen.kent at
Wed Dec 28 14:32:33 UTC 2011

Most vendors have a TCAM that by default does IPv6 routing for netmasks <=64.

They have a separate TCAM (which is usually limited in size) that does
routing for masks >64 and <=128.

TCAMs are expensive and increase the BOM cost of routers. Storing
routes with masks > 64 takes up twice the number of TCAM entries as
the routes with masks <= 64. Since IPv6 is *supposed* to work with /64
masks, most vendors (usually the not-so-expensive-routers) provide a
smaller TCAM for > /64 masks.


On Wed, Dec 28, 2011 at 6:40 PM,  <sthaug 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.
> Steinar Haug, Nethelp consulting, sthaug at

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