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Designing DHCP agent redundancy

Hi all.

I am using a router to act like a relay agent between a dhcp server and a cpe. This is done to provide voip service (SIP) to customers. There are multiple unnumbered interfaces(one per site) which use as a gateway interface, a specific loopback. The current config looks like that:

interface GigabitEthernet0/0/2.xxxxx

encapsulation dot1Q xxxx second-dot1q xxxx

ip vrf forwarding xxxxxxx

ip dhcp relay information trusted

ip unnumbered Loopback350012011

ip helper-address xx.xxx.xxx.xx

Since i have a second router of a similar operating function i am trying to find a way to make this service redundant. The two routers are connected to a single switch from which they receive the traffic from the cpes.

One problem is to redirect the user to a "mirror" interface of the second router if the first one fails. However Hsrp cannot be configured as far as i know to ip unnumbered interfaces.

The second problem that is pretty clear is that even if this could be done the second router would not have the appropriate info so as to route the CPE.

When the relay agent(router 1) is operating as an intermediate of the client/server communication, it creates the appropriate static route for as long as the lease time lasts. So the second agent(router) that doesnt take part in this would have no way to hanndle an already given ip of a connected cpe. It would need to wait untill the leased time exprires and the cpe reconnects to the second router.

dhcp_redun.jpg

I have done some research but havent found any example like this. Are there any ideas on how would that be possible?

Regards

Alexandros

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