CoS on Layer 3 interface

Unanswered Question
Jan 16th, 2008

We have recently switch MPLS providers and they are requiring that we use CoS tagging on our router interfaces. All of our sites use 1800 or 2800 series routers. When I create all of the maps and attempt to apply the CoS to the interface, ny routers inform me that you cannot apply CoS to a layer 3 interface? I cnnot seem to find any CoS examples on a layer 3 interface. Zny help would be greatly appreciated.

I have this problem too.
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dionh Wed, 01/16/2008 - 15:02


CoS is Layer 2 only. Try using ip precedence or DSCP both are layer 3.

match dscp and set dscp


jacutis Wed, 01/16/2008 - 15:10

Now, since _T&T are looking for CoS tagging value specifically, can I set it on my connected switch and pass it along to the router for forwarding since the switch is layer 2?

dionh Wed, 01/16/2008 - 15:24

Yes and No; you can read the CoS information from the switch as it passed to the router but layer 2 header information is removed so you have to re-mark the packets with layer 3 information.

so you would read the COS information from the packet and re-classify and then mark the packets with DSCP or IP Precedence and then foward them across your WAN.

Like wise the router can mark packets with CoS leaving you routers interface; but to honest most Layer 2 devices support DSCP IP & Precedence markings.

Hope this helps



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