How do I configure the Catalyst 2950 series switches with voice VLANs for Cisco IP phone connections?
A. For Cisco IOS Software Release 12.1(12c)EA1 and later, when you configure the 2950 as an access layer switch for voice, first modify the default class of service (CoS)-to-differentiated services code point (DSCP) mapping table so that: • CoS 3 maps to DSCP 26 • CoS 4 maps to DSCP 34 • CoS 5 maps to DSCP 46 Next, enable voice and data VLANs on the phone port and set the IP phone trust boundary. Issue the mls qos trust cos command from the IP phone. Finally, modify the CoS-to-egress-queue mapping and enable the expedite queue. With enablement of the expedite queue, voice packets always receive service before all other packets. Here is a sample configuration: c2950(config)# mls qos map cos-dscp 0 8 16 26 34 46 48 56 c2950(config)# mls qos bandwidth 10 20 70 0 c2950(config)# interface fastethernet 0/1 c2950(config-if)# mls qos trust cos c2950(config-if)# switchport voice vlan 100 c2950(config-if)# switchport access vlan 10 c2950(config-if)# switchport priority extend cos 0 Also, the aut
