Guarenteeing bandwidth to select traffic?

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I have need to set up some QoS for a particular interface. Our network isnt configured for QoS as yet, so this will be a one-off limited implementation.

The router is a 3825 running 12.4. Behind the router are a number of networks in the 10.2 range. The router connects to a central site. The WAN link is 10mb fibre.

Any traffic originating from should be guarenteed bandwidth up to 5mb/s. However, if using bandwidth in excess of 5mb/s, the burst traffic should have a lower precedence than any other 10.2 traffic. So basically 10.2.2.x has 5mb of guarenteed bandwidth, and can burst up to the maximum available only if noone else is using it.

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robertblasey Wed, 06/04/2008 - 23:34
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Hi anonymous,

when you write "should have a lower precedence" do you want your router to mark the packets with a certain ToS/DSCP value so your provider can drop the right packets in case of congestion, or do you want your router to actively drop packets in case 10.2.2/24 traffic exceeds 5MB in the presence of other 10.2/16 traffic?


PS: in case you have 10mb 10.2.2/24 and 5mb 10.2/16 traffic - which packets would you like to see on the WAN link?

Joseph W. Doherty Thu, 06/05/2008 - 05:27
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What you might do is, upon ingress to the 3825 use a policer to mark packets differently based on whether the rate is within 5 Mbps or not.

On 3825 egress use a CBWFQ class that matches either or the two markings you're using (assuming their unique to just that traffic), define class bandwidth for 5 Mbps, use WRED to drop over 5 Mbps packets almost immediately (e.g. min/max = 1/2), use default drop for other packets. (Also insure class-default isn't using FQ.)

If you handoff to the WAN is faster than actual bandwidth end-to-end, also use a hierarchal shaper.


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