[c-nsp] 6500/7600 TCAM Usage

[Pete Lumbis]

The TCAM on Sup2t isn't the same as Sup720. The Sup2t stores routes as a
data structure in a memory pool, which means that it isn't a fixed number
of route entries, but is based more on the prefix distribution and how
routes are added/deleted. I don't remember the specifics but it is possible
to run out of space before hitting datasheet numbers if you're really
unlucky.

This is in contrast to Sup720 where there is a single fixed bank for each
entry. 512k banks = 512k routes. Never any less.

As you start getting close to the ceiling on Sup2t the risk of suddenly
going over is much more real than it would be on Sup720.


On Tue, May 31, 2016 at 2:19 PM, James Bensley <jwbensley at gmail.com> wrote:

> Hi All,
>
> In a similar vein to the concurrently running thread about a SUP-2T-XL
> thinking it is out of TCAM space...
>
> What are realistic usage levels for TCAM on 6500 and 7600s RSPs? We've
> got some 7600s running RSP720-3CXL-10GEs and they are at nearly 80%
> utilisation (74%-78% off the top of my head).
>
> Ignoring the fact that one can partition a certain percentage for IPv4
> or IPv6 or multicast space. I mean overall can we actually use 1
> million TCAM entries?
>
> I have asked TAC and they said the TCAM can be 100% used, not until we
> have 1,024,000 entries in TCAM will we start of see the syslog
> messages for failing to install a prefix. I am certain that one CAN
> NOT use 100% of the TCAM space, I'm sure I read somewhere that at
> around 90% utilisation we start so process switch / drop packets /
> fail to install routes.
>
> I obviously can’t find any Cisco documentation on saying we can’t use
> 100% of the TCAM. TAC have said we can use 100% of the TCAM. I still
> don’t believe this, I’m so certain I have read somewhere that we
> can’t.
>
> Has anyone had any experiences relating to this they can comment on?
>
> Cheers,
>
> James.
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