Configure DHCP Option 120 using FQDNs

This article explains the steps to follow in order to configure DHCP Option 120 using FQDNs

DHCP option 120 can be configured as follows:

1. Decimal Values

   Select "120 (SIP Servers DHCP Option)" for "Option Number"
   Select "Option Array"
   Select  "One Byte Data" for "Option Type"
   Enter the following string   0; 7; 101; 120; 97; 109; 112; 108; 101; 7; 101; 120; 97; 109; 112; 108; 101; 3; 99; 111; 109 as option value (decimal value for example.example.com)

1. HEX Values

   Select "120 (SIP Servers DHCP Option)" for "Option Number"
   Select "Option Array"
   Select  "One Byte Data" for "Option Type"
   Enter the following string   0x00;0x65;0x78;0x61;0x6d;0x70;0x6c;0x65;0x2e;0x65;0x78;0x61;0x6d;0x70;0x6c;0x65;0x2e;0x63;0x6f;0x6d;0x00 as option value (decimal value for example.example.com)

Note: The domain name needs to be converted first (split domain name and then convert to ASCII value)

To use more domain names of SIP Servers (i.e. sip.dell.com, domain.test.com)

1. Convert the domain names
   1. sip.dell.com is 3, 's', 'i', p', 4,'d', 'e', 'l', 'l', 3, 'c', 'o', 'm' 0 is 037369700464656c6c03636f6d00
   2. domain.test.com is 6, 'd', 'o', 'm', 'a', 'i', 'n', 4, 't', 'e', 's', 't', 3, 'c', 'o', 'm', 0 is 06646f6d61696e047465737403636f6d00
2. Concatenate the two strings and add "00" first.
3. So, the result is:
      Option Type:Hex String
      Option Value:00037369700464656c6c03636f6d0006646f6d61696e047465737403636f6d00