FortiGate DHCP DNS suffix

The primary DNS suffix is the DNS namespace which a computer belongs to. This is normally handed out by DHCP server, for example on a windows device DHCP server belonging to a domain mycompany.local on the DHCP server under scope options a domain name of mycompany.local would be included to be assigned to clients.

When running ipconfig /all on a client machine under  “Connection-specific DNS Suffix” the primary DNS suffix that has been assigned can be viewed. The client then uses this suffix in DNS queries,  for example, if doing a remote desktop connection to only the computer name  RDS01 the computer adds the suffix to query the DNS server for  the IP address of RDS01.mycompany.local

Adding this DNS suffix via a FortiGate DHCP can be done by

  1. Create the DHCP scope in GUI
  2. In command line
    1. Config sys DHCP server
    2. Show (verify which DHCP scope to add the DNS suffix)
    3. Edit 1
      1. Set domain mycompany.local
      2. End
  • Clients will then get the DNS suffix when assigned an IP address

FortiOS 5.4.1

This is able to be accomplished in the GUI,  under DHCP on the interface click advanced > Additional DHCP option add Options Code 15 and put DNS suffix in the Value field.

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