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New Member

QOS on a 3640 Fast Ethernet Interface.

I am looking upgrade an existing serial WAN connection and replace it with a point to point Fast Ethernet LAN segment. We are currently not using QOS but would like to implement it with the use of two 3640’s

I have carried out a lot of research and I seem to find conflicting information on QOS over an Ethernet Interface.

The solution I have come up with is to use LLQ and DSCP to mark the service type.

Please can some confirm that this implementation is correct or point out the failings of this solution… If you can give me some guidance on thing to look out for it would be much appreciated…. Many thanks

New Member

Re: QOS on a 3640 Fast Ethernet Interface.


The exact QoS configuration you need is dependent on the type of traffic you want to prioritise, and therefore quite subjective. LLQ works well in most cases,and you have the priority command in the policy map to allow voice absolute priority. Assuming F0/0 is your LAN Side on the first 3640, and F0/1 is the replacement for the serial line, as long as you either know what the diffserv values of your lan traffic are, i.e. the application marks the traffic (not usually the case) or you explicitly mark the traffic (normal procedure) on the ingress to f0/0 you can pretty much do what you want.

You have loads of options on marking the traffic, such as NBAR, access lists, source interfaces etc, and then you just set the class of traffic to the diffserv value you want, then expidite the traffic out of f0/1 with any type of QoS you like.

The procedure is;

Marking and classification

Class-maps to find the traffic, Policy map to set the DSCP value, Service policy input on your LAN side


Class maps to match the DSCP value you have set, policy maps to define link bandwith per class, (or traffic shaping and policing values), and an output service policy on your outbound LAN interface (f0/1) to apply this.

There's loads of examples on CCO for you to try.