CCNA Voice Study – IP Phone Boot Process

  1. Phone connected to Ethernet switch port. Receives power either via 802.3af or Cisco-Proprietary POE.
  2. Cisco switch delivers voice VLAN information to the phone via CDP.
  3. Phone now in voice VLAN initiates DHCP request. Switch relays this to DHCP server via ip-helper command.
  4. DHCP server offers phone IP address including DHCP option 150, better known as TFTP server.
  5. Phone initiates a connection with the TFTP server provided in option 150 of the DHCP response and downloads its configuration file. Included in the configuration file is a list of call processing agents such as CUCM Subscriber, CME ISRs.
  6. The phone attempts to contact and register with the first call processing agent, if this fails it moves onto the next until the list is exhausted.

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