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I'm trying to use DHCP to configure several machines with two NICs. Each machine is multi-homed through one NIC to a network containing the DHCP server. The second NIC is connected to an isolated network. The two network cannot be connected. I would prefer to not use bridging on any machine in the cluster.

What software and configurations (e.g. iptables) can I use to achieve this? I've read about 'dhcrelay', but this appears to be fairly out of date tool.

Target distribution: Ubuntu 9.10

The topology:


Network A: contains DHCP server Network B: only connects nodes in the cluster


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up vote 1 down vote accepted

unless you set up a DHCP server on network B this config is going to cause you a world of pain.

An alternative is to put a second nic in your DHCP server and connect it to network B. Then you can have two DHCP zones, serving out two different address ranges.


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Dual-homing the DHCP server is our current solution, however, the inability for DHCP/?? to handle this scenario seems odd. In particular reason off hand, or just part of the spec? – Noah Watkins Feb 18 '10 at 0:51
It's not a problem with DHCP, it's got to do with how networks work in general. Two disjointed networks (which you have here) will never, ever, be able to communicate with eachother unless you do some sort of bridging/routing to do this, and you've already stated that you can't do bridging. – Mark Henderson Feb 18 '10 at 0:52
I would argue that it is not the fault of any inherent functionality of a network that prevents this: nothing prevents a person from designing a daemon that explicitly requests configuration information from a known source, and applies that configuration to the local client. I agree that bridging and routing is required. This can occur at the network or host level. – Noah Watkins Feb 18 '10 at 1:01

dhcp relay software is "out of date" because it is simple. We use "DHCP Relay" or "UDP Helper" configurations in our routers to do this currently, but in the past we have run dhcrelay at various sites and they just work.

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