[c-nsp] 6500/7600 TCAM Usage

[Gert Doering]

Hi,

On Tue, May 31, 2016 at 07:19:22PM +0100, James Bensley wrote:
> 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.

You can use 100% of what you have partitoned for - so if you partion for
512k IPv4, you'll blow up at 512*1024 IPv4 routes (minus a few, I'd
assume).  Been there, done that - not at 512k but at something like 200k
on non-XLs, years ago.

That "at 90% utilization bad things will happen" sounds like an urban
legend from the BNC ethernet times...  it's TCAM, there is nothing magic
about 90% - either a route can be poked in there, then it will work,
or not, then all excess routes will be process switch (and subject to
rate-limiting)

> 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.

You can't use 100%, as you'll never get the partitioning right...

gert
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USENET is *not* the non-clickable part of WWW!
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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