QoS - shaping question

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Aug 24th, 2008
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Hi - I have a wan which is a MPLS cloud. Access to the cloud from the router is for instance a 100M ethernet connection however we pay the provider for say 10M access. I want to ideally shape my outbound traffic to 10M and I don't want any packets to exceed as my service provider drops all packets exceeding 10M. My questions are should I shape on my outbound ethernet interface to 10M or should I police my outbound interface to 10M so I can decide what gets dropped. If I shape - is the correct command using the "shape average 10000000" or should I use "shape peak 10000000"?


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Jon Marshall Sun, 08/24/2008 - 20:41
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I would recommend using shaping rather than policing as this smooths out the traffic flow and is a less drastic option that simply dropping the packets (assuming that is what you were going to do with policing).

Where i last worked we had a number of BT 100Mb LES lines into MPLS and we only used portions of the bandwidth. We used shaping on our end with the "shape average ..." configuration.


Joseph W. Doherty Mon, 08/25/2008 - 03:28
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Like Jon, I too would recommend shaping over policing.

With regard to your question of whether to use average shaping or peak shaping, depends on what your service provider is monitoring. Ideally, your service provider should be able to tell you what burst time intervals or burst sizes are being used. (This information would allow you to correctly configure the other traffic shaper parameters.)

Recently, just had an issue with a MPLS provider, using Ethernet handoff, where their policed speed also counted all ethernet overhead, including interfame gap and preamble. They suggested shaping at about 95% of the specified rate. Something you might want to check with your provider.


BTW, policiers seem to usually operate much like a "short" single FIFO queue, while shapers seem to usually opeate much like FQ or WFQ.


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