| 1. | How does a Catalyst switch detect that a connected device is capable of using Power over Ethernet? |
| Answer: | The device first must loop the Ethernet connection's transmit and receive pairs. The switch then can hear its own test tone, confirming that the device does need inline power. When the power is enabled on the port, the switch and the device can exchange CDP messages so that the amount of power can be adjusted. |
| 2. | What type of trunk can be used between a Catalyst switch port and a Cisco IP Phone? |
| Answer: | A special-case 802.1Q trunk with only two VLANs |
| 3. | When a trunk is used on an IP Phone, on which VLAN is the data from an attached PC carried? |
| Answer: | PC data always is carried over the native (untagged) VLAN in the trunk. Voice packets can be carried over the native VLAN, too, or over a unique voice VLAN. |
| 4. | What is the difference between the VVID and the PVID? |
| Answer: | VVID refers to the voice VLAN ID, whereas PVID refers to the port VLAN ID. |
| 5. | Can the CoS information from the voice traffic be passed when the switchport voice vlan untagged command is used? If so, how? |
| Answer: | Yes, CoS information is passed within the 802.1p portion of the 802.1Q trunk encapsulation. |
| 6. | What is the advantage of using the switchport voice vlan dot1p command? |
| Answer: | Voice traffic is carried over VLAN 0 on the IP Phone trunk, so a unique voice VLAN is not necessary. This can be an advantage when a new VLAN can't be added to a network or switch. CoS information still is carried over the trunk in the 802.1p field. |
| 7. | By default, does a Cisco IP Phone trust QoS information from an attached PC? |
| Answer: | No. The phone will overwrite all QoS information (both CoS and DSCP) to 0, considering the PC an untrusted source. |
| 8. | The command switchport priority extend cos 5 is entered for a switch port. Is this a good decision? Why or why not? |
| Answer: | Probably not. After that is done, all packets from an attached PC will be marked with CoS 5, the same value the phone gives to its voice-bearer packets. Any upstream switches will be incapable of distinguishing the two types of traffic just by examining the CoS value. |
| 9. | The show power inline command is used to check the power status on each switch port. If the output is as shown here, what can you assume about interface fastethernet 0/1? Interface Admin Oper Power Device (Watts) ---------- ----- ---------- ------- ------------------- Fa0/1 auto off 0 n/a Fa0/2 auto on 6.3 Cisco IP Phone 7960
|
| Answer: | Interface fastethernet 0/1 shows an operational inline power state of "off," with 0W of power. This could mean that nothing is plugged into that switch port. It also could mean that an IP Phone is connected to the port but that the port has inline power set to the "off" state. |
| 10. | What command can verify the QoS trust relationship between an IP Phone and its attached PC? |
| Answer: | show mls qos interface or show interface switchport |
