How to configure DHCP Server on Cisco IOS

Lessons Discussion
46

Hello Cameron

You can find all of the DHCP options at the Internet Assigned Numbers Authority (IANA) since they officially define them. You can see the list here:
https://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml

As for information about DHCP options for the most essential services, it depends on what you mean by “essential”. For IP phones, the most often used options are:

When configuring IP phones using DHCP, specific DHCP options are commonly used to ensure that the phones receive the correct configuration and can connect to the 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):

    • Provides the IP address or hostname of the SIP (Session Initiation Protocol) server, allowing the IP phone to register and initiate calls.

  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 timezone.

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

    • Provides the IP addresses of NTP servers for the IP phone to synchronize its internal clock.

  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. For other requirements, let us know and we may be able to create a NetworkLessons note about the most often-used DHCP options.

I hope this has been helpful!

Laz