Matching on what value for QoS-ports or dscp values

[nygenxny123]

I have seen 2 different types of matching for class maps when implementing QoS...particularly for voice

one is building and ACL for selected ports than marking them with a dscp value on the incoming port..than 

applying whatever QoS restrictions you want.

ex:-ip access-list extended SCAVANGER
permit tcp any any eq 1214
permit udp any any eq 1214
permit tcp any any range 2300 2400
permit udp any any range 2300 2400

class-map match-any SCAVENGER-QUEUE
match access-group name SCAVANGER

the other is matching on a dscp value..than applying your QoS restrictions

class-map match-any MULTIMEDIA-STREAMING-QUEUE
match ip dscp af31 af32 af33

My question is..which is better?....could you do both at the same time?

[Jon Marshall · Accepted solution]

They are different things.

If you use an acl to match them then that is either because the packets don't have a DSCP marking or you don't want to trust them.

If you match on DSCP then something else has marked the packets.

So you can either match the traffic or the DSCP marking and do something with it in the same policy.

Or you can match the traffic or the DSCP marking and remark it in the same policy but as far as I know you cannot then apply other QOS actions to those remarked values  ie. the markings would then be used in another policy on another interface or by another L3 device along the path.

Jon

[nygenxny123]

Thank you...that's what I thought. I couldnt understand how you could trust dscp on values unless somethign else had initially marked them..