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Process Switching

Unanswered Question

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

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svermill Wed, 01/02/2002 - 11:05
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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.



n.moss Fri, 01/04/2002 - 08:04
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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.

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