IP Communicator and QOS

Unanswered Question
Nov 3rd, 2008
User Badges:

Since IPC via CDP will announce itself, is the command

"mls qos trust device cisco-phone" on a 2950 enough for it to trust the DSCP from the PC attached? Will it then trust the DSCP value for all traffic or just voice / signaling traffic?

I guess I would still need to program the egress queues to prioritize the traffic as it leaves to go upstream to gatways, other phones , etc.

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Brandon Buffin Mon, 11/03/2008 - 13:03
User Badges:
  • Purple, 4500 points or more

No, this command will only trust the DSCP values of a physical Cisco phone and not the PC behind it. Traffic from IPC is essentially data traffic. Take a look at the QoS SRND below. See the Campus QoS Design section for example configurations for classification and marking of IPC traffic.


Hope this helps. If so, please rate the post.


allan.thomas Mon, 11/03/2008 - 14:05
User Badges:
  • Blue, 1500 points or more

All traffic from the IPC software based endpoint will be classified with the correct DSCP including voice and signalling.

For this reason Cisco recommends configuring the policy map to trust the DSCP marking of incoming traffic and then apply traffic policing and rate limit the amount Voice and Signalling.

The limitation with the 2950 is that policing is only configurable within 1Mpbs intervals which is somewhat excessive and can be used maliciously if the device attached is not IPC endpoint.

In such circumstances it is recommended to do ACL marking and policing at the distibution layer.

If it is possible to re-mark on the 2950 with the correct image, then ensure that your ACLs are granular enough to match signalling and voice media and then set DSCP accordingly rather than trusting the DSCP.




This Discussion