DHCP - Commonly used options for IP phones

When configuring IP (VoIP) phones using DHCP, specific options are commonly used to ensure that the phones receive the correct configuration and can connect to necessary services, such as VoIP servers. Here are the most often used DHCP options for IP phones:

  1. Option 66 (TFTP Server Name):

    • Specifies the IP address or hostname of the TFTP server from which the IP phone can download its configuration file.

  2. Option 150 (TFTP Server Address):

    • Similar to Option 66, but allows specifying multiple TFTP server IP addresses. This option is often used in Cisco IP phone deployments.

  3. Option 3 (Router):

    • Provides the default gateway that the IP phone should use to communicate with other networks, including the VoIP server.

  4. Option 6 (Domain Name Server):

    • Specifies the IP addresses of the DNS servers that the IP phone should use to resolve domain names.

  5. Option 120 (SIP Server):

  6. Option 144 (Telephone Number Mapping (ENUM) Service):

    • Allows the IP phone to obtain ENUM information, which maps phone numbers to IP addresses using DNS.

  7. Option 2 (Time Offset):

    • Specifies the offset from UTC in seconds, used by the IP phone to display the correct time based on the phone’s time zone.

  8. Option 42 (Network Time Protocol (NTP) Servers):

  9. Option 15 (Domain Name):

    • Supplies the DNS domain name, which the IP phone can use as part of its fully qualified domain name (FQDN).

  10. Option 4 (Time Server):

    • Specifies the IP addresses of the time servers that the IP phone can use, although NTP servers (Option 42) are more commonly used.

These DHCP options help automate the configuration process for IP phones, ensuring they can connect to necessary services and function correctly.

Links:

https://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml

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