5 Replies Latest reply on Oct 25, 2012 2:40 PM by daniel.blackmon

    Set to forward any dhcp requests to another dhcp server

    georanma New Member

      Just got set up with a unit from my ISP. One of the first things I havent been able to figure out is how to forward any dhcp requests to another server that we have handling any non static assignments. I was able to set the ip of the router to an ip without our private network and can now use it as a default gateway for computers to connect to.


      Eventually, I need to move my pbx server over to using that as a gateway and figure out why calls arent working once I connect to it as the gateway for said server.

        • Re: Set 3133 to forward any dhcp requests to another dhcp server
          cj! Beta_User

          Hi georanma:


          Is it a 3130?  Sounds like you might have two challenges.  DHCP relay is pretty easy.  This is used when you would like a DHCP server on one network (broadcast domain) to hand out addresses for hosts on another network.  Your concern about using the unit as a gateway for voice traffic might be better addressed in its own discussion, where more info and detail can be shared.


          UDP Relay is found in the web GUI in the Data section.  Basically, you enter in the top item the IP address of the DHCP server you want to forward DHCP requests to.  Use the pull-down below that to choose which interface (VLAN 1, or eth 0/1, or whatever you need) will listen for DHCP requests to be forwarded.  Click Add.  In the lower section, choose BOOTPS (67).  BOOTPS means DHCP requests.  Remember to Save your changes.


          Check out this ADTRAN guide for UDP Relay for more info and CLI examples.





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          • Re: Set 3133 to forward any dhcp requests to another dhcp server



            Thank you for posting this question in the support community. 


            Many services, such as DHCP, rely on clients being able to reach a server by broadcasting a request. These requests are limited by being broadcast. Broadcast traffic propagates only throughout the local subnet. If the client is not on the same subnet as the server, the broadcast will not reach the server. If it is necessary for clients to have the ability to communicate with a remote server through broadcast traffic, then UDP Relay must be enabled. UDP Relay, once set up, will not simply forward the broadcast packets. It also examines them, checks their validity, and adds any appropriate changes, such as its own IP address (which enables the server to return the traffic to the router). The router will then forward this traffic to the client.


            UDP forwarding gives the network administrator the ability to have centralized services. For example a network with several routers/subnets does not need a DHCP server on every subnet. The DHCP address negotiation can be forwarded to a central DHCP server configured for multiple scopes. The administrator now has a single point of address management. The router responsible for UDP forwarding will receive a UDP broadcast and then forward the packet as a UDP unicast to a specified IP address.  More detailed information about UDP relay can be found in the Configuring UDP Relay in AOS document.


            Configuring UDP forwarding consists of two commands:


            • The ip helper-address <ip address>command is applied to the interface where the UDP broadcast packet originates and will enable UDP broadcast forwarding. The interface will forward received UDP broadcast frames to the unicast IP address specified in the ip helper-address command. The forwarded packet will use the IP address of the interface as it source.


            • The ip forward-protocol udp <value> command will globally define which UDP protocols to forward based on UDP port number. Some protocols can be specified by name for ease of configuration.


            For example, if the remote DHCP server has an IP address of, then the interface of the ADTRAN that receives the broadcasted DHCP traffic will need to be configured with the ip helper-address <ip address> command.


            ROUTER-NAME(config-eth 0/1)# ip helper-address


            Then you have to configure what ports need to be forwarded, in your case domain and bootps:


            ROUTER-NAME(config)# ip forward-protocol udp domain

            ROUTER-NAME(config)# ip forward-protocol udp bootps


            I hope that makes sense, but please do not hesitate to reply to this post with any additional questions.  I will be happy to help in any way I can.



            • Re: Set to forward any dhcp requests to another dhcp server
              daniel.blackmon Employee

              It may be helpful to note that as of AOS version 18.02, a new command was added to simplify the DHCP relay process. From the interface level configuration prompt, the following command can used to enable DHCP relay.


              ROUTER-NAME(config-eth 0/1)# ip dhcp relay destination <address>

              This configures the Adtran equipment to act as a DHCP relay agent for the specific interface while still allowing the Adtran equipment to act as a DHCP server on other broadcast domains. In other words, the Adtran equipment can act as a DHCP server for certain VLANs, while forwarding the messages for others. The setup is likewise simpler, however currently it must be done through the CLI.

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