[c-nsp] 6500 latency

[Mack McBride]

The lowest conceivable latency for a 1500 byte packet on 1GE is 12usec in a store and forward mode.
This does not include inter-frame gap or other overhead (ie. Switching).
This is simple physics.  You need to go to 10GE for really lowering latency.

LR Mack McBride
Network Architect
Viawest, Inc.

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Jeff Bacon
Sent: Tuesday, April 27, 2010 6:56 AM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] 6500 latency

OK, I know that a 6500 is not a super low latency box. I've seen around 17usec, card to card to another switch CFC mode, but due to time constraints have done little formal analysis. 


I'm guessing its better in DFC mode, and on 6700 cards, and if your traffic is local to a card or to a fabric port such that it doesn't have to traverse the fabric. 

I'm also guessing that sup32s and anything on classic bus (including the two interfaces on the sup720) aren't super-high latency either. 

Has anyone done any work on what the overall parameters are on a 6500's switching latency? Or got a pliable cisco rep who can get me to someone who can unlock those documents? 

Clearly Cisco has, to the extent that a cisco exec told me yesterday that they see no role for the 6500 in low-latency financial market apps except in edge cases where NAT is needed and even then I should consider an ASR (of course they need to sell more nexii I imagine - but what, am I made of money???). Strangely, though, I find them highly reticent to share anything about the actual facts of the matter. Maybe they're annoyed that I buy mostly refurb gear. :) 

(Then again, I tend to find that most micro-level-latency talk to be half marketing fluff and mantra, and/or an excuse to spend a ton more money on product X.)

It's a shame that most exchanges force me to NAT to talk to them unless I want to do Really Stupid Things with my network, or talk ARIN out of a /22. Which is why I have 6500s everywhere (and sometimes wonder about the wisdom thereof, given the costs).

OK, I admit I am ranting.
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