How to configure a Voice-over-IP (VoIP) network on the Cisco Catalyst 6500 series switches

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Resolution

These guidelines apply to auxiliary VLAN configuration:

• An auxiliary VLAN port is operationally a trunk, even though it is not treated like a normal trunk port.

  When an auxiliary VLAN is added to a port and the set dot1q-all-tagged command is enabled, the set dot1q-all-tagged command tags the native VLAN on the port where the auxiliary VLAN is configured. A port with an auxiliary VLAN configured is not viewed as a dot1q trunk in the show trunk command output, but the port acts like a dot1q trunk if the set dot1q-all-tagged command is enabled.

• The IP phone and a device attached to the phone are in the same VLAN and must be in the same IP subnet:
  • If they use the same frame type
  • If the phone uses 802.1p frames and the device uses untagged frames
  • If the phone uses untagged frames and the device uses 802.1p frames
  • If the phone uses 802.1Q frames and the auxiliary VLAN equals the native VLAN
• The IP phone and a device attached to the phone cannot communicate if they are in the same VLAN and subnet, but use different frame types. This is because traffic between devices in the same subnet is not routed (routing eliminates the frame type difference).
• Switch commands cannot be used to configure the frame type used by traffic received from a device attached to the phone access port.
• With software releases 6.2(1) and later, dynamic ports can belong to two VLANs, a native VLAN and an auxiliary VLAN.

For more information on how to configure auxiliary VLANs, refer to the Configuring a VoIP Network section of Configuring a VoIP Network.

Problem Type

Configure

Catalyst switch

Catalyst 6500 series switches

Switch software

CatOS system software

Software features

Quality of Service (QoS)

Device connected to switch

Cisco IP Phone

Connected to same switch or different switches

Same switch