ASA // shaping vs. policing

Unanswered Question
Apr 24th, 2009


I'd like to apply individual shaping for different classes of traffic which are traversing an ASA.

The documentation of ASA (8.0) tells me that "Traffic shaping must be applied to all outgoing traffic on a physical interface or in the case of the ASA 5505, on a VLAN. You cannot configure traffic shaping for specific types of traffic."

So that means I can't divide the traffic into smaller subsets (for instance, IP-subnets) and shape them individually. I could do policing instead.

The problem I see here is that I have had bad experiences with policing in regards with performance of TCP-sessions. It's no surprise: If there is a threshhold over which every packet is just dropped, it triggers TCP to drop down and after a while to "build up" the used bandwidth, resulting in a sawtooth-pattern in used bandwidth. Shaping is much better in this regards, as it smoothens the used bandwidth perfectly to the set threshhold.

I could imagine that this problem is neglectible if there is a number of clients large enough falling into one class, as the problem distributes over more clients, but this is not always the case.

Can anybody please give some input here on how to tackle this problem, e.g. how to make policing work better or alternative solutions?

Thanks a lot,


I have this problem too.
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Anonymous (not verified) Thu, 04/30/2009 - 11:58

I think you can configure "service-policy (class)" coomand on ASA for traffic shaping. Hierarchical priority queueing is used on interfaces on which you enable a traffic shaping queue. A subset of the shaped traffic can be prioritized. The standard priority queue is not used (the priority-queue command).


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