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New Member

Guarenteeing bandwidth to select traffic?

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.

New Member

Re: Guarenteeing bandwidth to select traffic?

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?

New Member

Re: Guarenteeing bandwidth to select traffic?

Thanks for the reply Robert.

Our carrier doesnt currently support qos tagging on traffic. So i'm just after controlling the traffic on the egress interface. I'd prefer to shape the traffic rather than just drop it if possible. However if dropping the excess traffic is the only option, then ok.


Super Bronze

Re: Guarenteeing bandwidth to select traffic?

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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