Configuring DHCP Relay Configuration Example Alcatel-Lucent Security Products Configuration Example Series

Configuring DHCP Relay DHCP (Dynamic Host Configuration Protocol) is an administrative tool that prevents the need for “fixed” IP addresses each PC on the network. As you can imagine this saves administrators a great deal of time with assignments, adds, moves and changes. DHCP Relay is an industry standard approach to relaying DHCP requests as uni- cast messages. DHCP requests are sent from the prospective client PC as a broadcast. As broadcasts increase network traffic the need for the DHCP Relay protocol became apparent. DHCP Relay is primarily used to keep traffic off of WAN ports and is commonly used in routers and firewalls.

Configuring DHCP Relay When a DHCP client wishes to obtain an address from a DHCP server, it broadcasts a request on the local LAN. If there is a DHCP server on the same LAN, then it responds to the request. However, if a DHCP server is outside the LANs protected by a Brick, the client request needs to be forwarded through the Brick to the server. The DHCP Application filter enables the DHCP client request to be forwarded as a uni- cast message to a DHCP server located in another network. The Bricks support many DHCP Features. This configuration example will show how to configure a Brick to supply DHCP relay.

Configuring DHCP Relay There are only a handful of steps to setup DHCP relay on the Brick. First get the addresses of the DHCP server or DHCP servers that you will be obtaining the dynamic IP Addresses from. Second setup the PC’s on the internal network to obtain an address automatically, as shown to the right. Once those steps are done you are ready to configure the DHCP Relay feature on the Brick.

Configuring DHCP Relay From the main AALSMS menu Click on Application Filters. Then Click on the DHCP_Relay Application filter. This is where you will add the IP Address or addresses of your DHCP servers. You can add up to two addresses for DHCP Servers separated by a comma.

Configuring DHCP Relay This application filter is attached to the “Service Group” called “DHCP_Relay”, which we will use in a rule on the next couple of slides. Fill in the address to your server or servers. Fill in the description. Click File>Save and Close.

Configuring DHCP Relay Next go to the Brick Zone Rulesets. Choose the rule set that is applied to the interface that your prospective client PC’s are connected to. In my case that is a rule set that I created called “inside-zone”. Yours will be whatever you named it. Double Click on your rule set to open it.

Configuring DHCP Relay Assuming that you have created all of the rules that you need for this interface and the subnet behind it, all you need to do now is to add a rule to allow the service “DHCP_Relay”. If you haven’t created the other rules yet, make this your first rule and proceed to the configuration examples on creating rules and rule sets. Remember we added the address to your DHCP server to the application filter that is attached already to the DHCP_Relay service group.

Configuring DHCP Relay The screen to the right shows the process of adding the rule. Once you are done here make sure to do a File>Save and Apply to the Brick and test your PC’s to see that they are getting dynamic addresses.

Configuring DHCP Relay From the command prompt on the PC you can type IPConfig to see the IP Address of the PC Other useful commands are “IPConfig /release” to release an address and “IPConfig /renew” to get a new address This is a good way to test to make sure that the PC is communicating with the DHCP Server

Configuring DHCP Relay The only other step that you may need to take is to create a “static” or “default” route on the Brick, depending on the relationship between your internal network and the network with the DHCP Server. If everything is working fine, skip this step. If you need to create a route, see diagram below.

Configuring DHCP Relay For more detailed information on configuring DHCP Relay see the AALSMS Policy Guide. You can access the manuals by clicking: Help>On Line Product Manuals>AALSMS Policy Guide. The Manuals can also be found on your AALSMS Installation CD.