[147936] in North American Network Operators' Group
Re: subnet prefix length > 64 breaks IPv6?
daemon@ATHENA.MIT.EDU (Glen Kent)
Wed Dec 28 09:33:25 2011
In-Reply-To: <20111228.141052.104056686.sthaug@nethelp.no>
Date: Wed, 28 Dec 2011 20:02:33 +0530
From: Glen Kent <glen.kent@gmail.com>
To: sthaug@nethelp.no
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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.
Glen
On Wed, Dec 28, 2011 at 6:40 PM, <sthaug@nethelp.no> 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@nethelp.no
>
