How to DSCP mark RTP / RTCP packets if RTP / RTCP ports are dynamically set?

[Sam Brynes]

I have layer 3 routing enabled on a Cisco 3750 switch and I have a Cisco 1921 router connecting to the public Internet.

Traffic from clients is first routed to the Cisco 3750 switch, and then out the 1921 router.

Where and how would I set DSCP markings on RTP and RTCP packets if those ports are dynamically allocated? I'm assuming on the router since it probably has some type of RTP / RTCP inspection that I can use? I think I have half the equation here, just hope that someone can help take me the rest of the way.

[Mohammed al Baqari]

You can set them on the switch using two ways:

1. Either you trust the marking from the phone on the switch using the
option cisco-phone to make sure that trust is limited to cisco phones.
Phones will mark the packets using the configuration from CUCM
2. configure an ACL on the switch to match voice subnets and rtp/rtcp port
range and set the dscp value on the switch as well.