Process Switching

karl.jones · ‎01-01-2002

Hi There,

If I apply access-lists to interfaces on a 3600 router, am I essentially turning off fast switching off for those interfaces as all packets have to be checked for matches or do access-list make no difference at all to fast switching. Also, how does priority queuing affect fast switching as it rearranges the order of packets.

Any advice appreciated

Karl Jones

svermill · ‎01-02-2002

Hello Karl,

Check out this link on switching. You want to look at netflow for combining access lists and maintaining some fast switching functionality:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/switch_r/xrswcmd.htm#xtocid46458

I hope someone else can answer the part of your question about priority queuing. I think that switching decisions and queuing decisions are apples and oranges but I can't say for sure.

karl.jones · ‎01-04-2002

Thanks Scott,

I will check out that link,

Happy New Year

n.moss · ‎01-04-2002

If im right, it doesn't affect fast switching at all. I know ACLs cannot be used with CEF switching unless in conjunction with a policy. The good thing is it would not instantly divert to process switching, it would drop to each previous switching successor in terms of speed. Not all packets would be process-switched anyway because the "stream characteristics", e.g. src/dest/port, etc. would be cached preventing the need for every packet from each stream being compared to the ACL.

Hope this helps,

Neil Moss.