round-trip time of ping between a access switchs.

[kevinzhang]

i have two 6509 as distribution switchs and just 2 4000 at the access layer. When I ping between access switchs or to distribution switch. The round-trip time I got is usally great than 8 ms. all the swiths are in same building and one access sw is next to a distribution sw. is this normal?

TIA

[Prashanth Krishnappa]

Pings (ICMP echo requests) going to the switch's sc0 interface have to be processed by the NMP software running on the switch, which then sends an ICMP echo reply. We chose to have the CPU spend most of its time doing things that are important to keeping the switch performing well, so 7-8ms is

about the quickest response time I'd expect to see on the Cat4000. On a very busy switch, I'd expect longer response times, because the CPU is off doing other things.

When you ping *through* the switch, the ICMP echo request is just another data packet that is forwarded by the switch hardware. The latency you'd expect

to see in that case is the round-trip forwarding delay through the switch

(usually very short, on the order of microseconds), plus the latency of the IP

stack you're pinging, plus any other delay in the network that the ICMP echo

request and reply have to traverse. The following page should help as well

http://www.cisco.com/warp/public/473/82.html#ping

Hope this helps