Extending COS markings to an IP Phone

ryannick1 · ‎07-21-2008

Could someone please help me understand this. When a PC is connected to an IP phone where does the cos overide take place if the switch is configured with "switchport priority extend cos 2" The documentation states that the IP phone access port overides the priority. Is this refering to the access port on the Catalyst that the IP phone is plugged into or is this the port on the IP phone that the PC plugs into?

http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_14_ea1/configuration/guide/swvoip.html#wp1030860

"Set the IP phone access port to override the priority received from the PC or the attached device."

michaelchoo · ‎07-21-2008

I believe the IP Phone will override any CoS/DSCP markings that it receives on the PC port. However, with the command that you mentioned in your original post, you're basically telling the switch to configure CoS value of 2 for all data packets received from the PC, but still leaving the IP phone-generated packets unchanged.

Any QoS expert out there that can vet this?