Resilient DHCP serving

Unanswered Question
Apr 29th, 2009

It is possible to use a pair of Cisco routers as a resilient DHCP server pair, both using the same address pool?

We are looking at setting a couple up as a HSRP pair, and it would be useful if they could both offer DHCP leases. The most ideal scenario would be a situation where they are aware of which leases the other has offered and not offer those ones.

The research I have done suggests the Cisco DHCP is very much a stand alone unit. Does anyone know any different?

I have this problem too.
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AxiomConsulting Wed, 04/29/2009 - 07:37

Just as a thought, you could add the same DHCP pool to both routers, and by using the 'ip dhcp excluded-address ' place half a pool on one router and the other half on the other router.....

HTH

davehartburn Wed, 04/29/2009 - 23:10

That is an option, or some people split it 80/20. The issue is you need to make sure both routers have sufficient space for your whole address space, to cover a long outage. This means you use twice as many IP addresses.

You can do a DHCP cluster with UNIX or Windows servers, though it would be cheaper and easier if we could do it with the hardware we already have.

Giuseppe Larosa Thu, 04/30/2009 - 00:19

Hello Dave,

we have used this kind of setup for some temporary remote sites.

A feature that can help is the configuration of a DHCP database agent that work as a file repository for DHCP bindings.

see

http://www.cisco.com/en/US/docs/ios/ipaddr/configuration/guide/iad_dhcp_svr_cfg_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1141816

in this case if a router should fail the other one can learn the bindings created by the failed node.

We haven't tried up to now but it looks like interesting.

Hope to help

Giuseppe

gnijs Thu, 04/30/2009 - 07:07

Guiseppe,

"in this case if a router should fail the other one can learn the bindings created by the failed node."

I am not sure about this. What are you trying to do ? Let both routers write to the same file and have the databases "merged" ? I doubt this will work (although the tought is appealing, interesting lab exercise :-)

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