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| 7.6 |  | Cisco IP Telephony |
| 7.6.9 |  | Connecting to the network with auxiliary VLANs |

The following steps outline the process that takes place when an IP phone is powered up and plugged into the network:

1. The IP phone begins a CDP exchange with the switch. The phone issues a trigger CDP to force a response from the switch. That response contains the VVID for the phone.
2. If the IP phone is configured to use DHCP (the default), it issues a DHCP request on the voice subnet it got from the switch. This is the recommended mode of operation. Static addressing can be used, but it prevents mobility.
3. The IP phone gets a response from the DHCP server in the network. Along with the DHCP response, which provides the IP address to the telephone, it is also possible to supply the address of the TFTP server from which the phone gets its configuration. This is done by configuring option 150 on the DHCP server and specifying the address of the TFTP server; Cisco DHCP server supports this feature. Again, it is possible to specify the TFTP server address manually, but this would limit adds, moves, and changes, as well as remove some other benefits.
4. The IP phone contacts the TFTP server and receives a list of addresses of Cisco CallManagers. Up to three Cisco CallManagers can be specified in the list. This provides redundancy in case the first Cisco CallManager in the list is not available.
5. The IP phone now contacts the Cisco CallManager and registers itself, receiving in return a configuration file and runtime code necessary for the phone to operate. For each configuration, the IP phone receives a directory number (DN) from the Cisco CallManager to be used for calling that particular IP phone.
6. The IP phone is ready to make and receive calls.