Reducing proces switching

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Feb 6th, 2008
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I have a 3825 with a fast ethernet interface and a nm-a1-t3 atm/ds3 interface. Most of the traffic is multicast traffic coming from the atm/ds3 and towards the fast ethernet. There is also a fair amount of regular IP traffic going both ways over the interfaces (about 5% of the traffic). The traffic is coming from and going to a limited number of locations.

"show interface switching" shows that a lot of the traffic coming in the atm/ds3 interface and out the fast ethernet interface is switched at the process level. A guess is that this is the multicast traffic is getting switched at the process level.

"show ip interface" shows that the atm/ds3 interface has IP multicast fast switching enabled but the fast ethernet interface has it disabled. Is this why it can't fast switch between these devices?

How would I enable IP multicast fast switching on the fast ethernet interface and is there any reason not to? Thanks.

-- Bud

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bbach1961 Wed, 02/06/2008 - 09:32
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Well, to anwer my own question (I think), the fast ethernet interface had "no ip mroute-cache" set. I changed that to "ip mroute-cache" and now, cpu usage has gone way down (8% to 4%) and it looks like most traffic is now being fast switched.

Any ideas on what this (process switch vs. fast switch) may do to latency?

-- Bud

Edison Ortiz Wed, 02/06/2008 - 09:52
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Process switch is processed by the CPU while Fast switch is processed by the hardware ASIC.

It's recommended to have Fast Switching enabled on interfaces at all times. It improves throughput and takes away processes from the CPU.





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