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Re: Film at 11:00
From: Ravi Chandra <rchandra () cisco com>
Date: Sat, 4 Jan 1997 01:51:10 -0800

In cisco.external.nanog you write:


not to make this too cisco specific, but...

the number of entries in the forwarding cache on the
sse is generally more than the number of routes in
the bgp rib (because of the way the cache handles
more-specifics of over-lapping aggregates).  so in
addition to the raw number of routes in the rib, the
efficiency (and scope) of aggregation are also
important data points

now a question.  what does an sse do when its cache
fills?  it used to(*) bring down the whole sse, which
doesn't really make much sense given that it's a
cache and therefore it's normal operation for it to
be incomplete.  anyone know an answer to that one?


SSE memory usage is monitored and if it falls below a particular
threshold, the ager will become more aggressive in aging entries..

--ravi


/jws

(*) -- "used to" implies that it happened before,
which it did.  but that was largely due to the
ineffeciency of the data structures, and the problem
was solved such that 2 years (and counting) was added
to its life


   Hmm, it's not news for us. 45K can hold core routing only as
   inter-back-bone router, not more.

   But why, why this crasy CISCO could not predict future when
   they designed 45K routers? It was not difficult  for them
   develop this box to cary 64 or 128MB RAM.

   >      Looks like the 45k mark was reached:
   >
   >   Folks with 7000's and SSE's should start monitoring their memory
   >   utilization via "show sse summary".

There's a couple of comments here:

First, 45k is not the limit.  More like 60k.  You'll pardon me for being
cautious. 

The limitation is not DRAM.  It's the 64k words of SRAM that the SSE uses
for its high speed forwarding table.  You don't want to pay for 64Mbytes of
SRAM.  ;-)

When cisco's engineers designed the SSE, we knew very well what was
happening.  We expected to be given the opportunity to produce subsequent
hardware which implemented the SSE in an ASIC.  If, by that time, CIDR
hadn't killed off the exponential growth, we would have expanded the
address space.  Unfortunately, cisco management decided that the SSE ASIC
should not be implemented (a mistake which, to my knowledge, cisco has not
corrected).  Thus, the 7500 exists without an SSE.

Tony
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