I have a network appliance (QNO) that works as traffic load balancer and dhcp server. I would like to add a linux server in between the network appliance and the client computers. The linux server will be used to monitor bandwidth usage.

My problem is I still want DHCP to be served by the network appliance so that load balancing will still work efficiently. We are afraid that if we setup the linux server as the DHCP server the network appliance will not be able to load balance the traffic if it only sees the linux server as a single client connecting to it.

I've been searching all over for a tutorial on how to setup DHCP relay but have not found any. How do I setup DHCP relay on my linux server given there are two NICs attached to it, one connects the linux server to the network appliance and the other connects the linux server to the client computers.


Router (DHCP) ----> [eth0] Linux Server (Relay agent) [eth1] -----> PC (network)

Router IP is eth0 is on DHCP eth1 is static (if I need to change this I can)

Tried to do dhcrelay -i eth1, but the PC was not getting any DHCP lease from the DHCP router.

I might be missing something here.


In the simplest case it is

dhcrelay -i <interface_towards_clients> <ipaddress_of_DHCP_server>

See the man page to dhcrelay for details.

  • for some reason this doesn't work on our setup – jerichorivera Nov 23 '11 at 0:41
  • dhcrelay is not rocket science, so it probably is fixed easily. Please post additional information about your setup (maybe some ASCII art with interface names and IP addresses) and the dhcrelay command line parameters you've used. – the-wabbit Nov 23 '11 at 15:19

Make sure you don't have a firewall blocking DHCP; it must be enabled on both the client-facing and the server-facing interface.

You must also configure dhcrelay to listen on both interfaces.

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