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Does ScreenOS support the IP Helper command?



Article ID: KB21571 KB Last Updated: 18 Aug 2011Version: 1.0
This article provides information about the support provided by ScreenOS for the IP Helper command.

Applications such as DHCP and NetBIOS, are applications which uses layer-3 broadcasts to communicate with the servers. In these scenarios the intermediate device needs to forward the same the layer-3 broadcast out of the interface. A very commonly used application is DHCP. Consider the following example:

Host A has to automatically obtain its IP configuration from the DHCP server at By default, the router will not forward the Host A DHCPDISCOVER which will be a layer-3 broadcast. Now for host A to receive the IP address from the DHCP server, the DHCP request from the client will have to be forwarded to the server. There are two way to achieve this purpose:
  • Transmit the DHCP traffic to the server using DHCP relay.
  • Forward the DHCP broadcast using the IP Helper command supported by other vendors.
The DHCP request, using the IP Helper command, can be relayed as a unicast to, or can be relayed as a broadcast to all servers on the segment -
The IP Helper command, by design, is not supported by ScreenOS.

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