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Re: Film at 11:00

  • From: John W. Stewart III
  • Date: Tue Dec 31 17:04:28 1996

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?

/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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