Cisco IP Phone Behavior

B.

Untagged traffic from the device attached to the Cisco IP Phone passes through the phone unchanged, regardless of the trust state of the access port on the phone.

When an IP phone is connected to a PC through its Ethernet port, the phone acts as a switch, allowing the PC to access the network through the phone's network connection. In this scenario, the phone may receive untagged data traffic from the attached PC.

In such a case, the phone can take one of the following actions:

A. It drops the traffic: If the phone is configured to drop untagged traffic, it will discard the packets received from the attached PC, and the PC will not be able to communicate with the network.

B. It allows the traffic to pass through unchanged: If the phone is configured to allow untagged traffic, it will forward the packets received from the attached PC to the network without any modification. This means that the packets will be sent with no VLAN tags, and the network will treat them as belonging to the native VLAN.

C. It tags the traffic with the native VLAN: If the phone is configured to tag untagged traffic with the native VLAN, it will add a VLAN tag to the packets received from the attached PC, indicating that they belong to the native VLAN. The native VLAN is the VLAN configured on the switch port where the phone is connected, and it is used for untagged traffic.

D. It tags the traffic with the default VLAN: If the phone is configured to tag untagged traffic with the default VLAN, it will add a VLAN tag to the packets received from the attached PC, indicating that they belong to the default VLAN. The default VLAN is VLAN 1, and it is used when no other VLAN is specified.

In summary, the action taken by the phone when it receives untagged data traffic from an attached PC depends on its configuration. It can either drop the traffic, allow it to pass through unchanged, tag it with the native VLAN, or tag it with the default VLAN.