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Any special configuration if doing DHCP and HSRP?

Imagine Router1 is currently a single WAN router and providing IP addresses via DHCP to clients in the LAN side.

Then I have to add a second router for redundancy. In the LAN side Router1 and Router2 will be configured with HSRP.

Question:

Is there any caveat or conflicts to be aware when using DHCP on both routers?

How the DHCP server configuration should be applied to both routers then since at certain point Router1(active) can go down and Router2 starts serving IP addresses to DHCP clients?

1 REPLY
Hall of Fame Super Blue

Re: Any special configuration if doing DHCP and HSRP?

news2010a wrote:

Imagine Router1 is currently a single WAN router and providing IP addresses via DHCP to clients in the LAN side.

Then I have to add a second router for redundancy. In the LAN side Router1 and Router2 will be configured with HSRP.

Question:

Is there any caveat or conflicts to be aware when using DHCP on both routers?

How the DHCP server configuration should be applied to both routers then since at certain point Router1(active) can go down and Router2 starts serving IP addresses to DHCP clients?

If you want to have both routers handing out IPs for the same subnet then you need to split the subnet in half so for example -

subnet = 192.168.5.0 255.255.255.0

default-gateway = 192.168.5.1

Router 1

=======

DHCP pool

192.168.5.1 -> 192.168.5.127 255.255.255.128

subnet mask 255.255.255.0

default-gateway 192.168.5.1

Router 2

======

DHCP pool

192.168.5.128 -> 192.168.5.254

subnet-mask 255.255.255.0

default-gateway 192.168.5.1

note that you are splitting up the subnet but you still hand out the same subnet mask and the same default-gateway for both pools.

Edit - don't forget you need to exlclude the other half of the subnet in each DHCP pool eg on Router 1 you would exclude IPs 192.168.5.128 -> 254 and on Router 2 you would exclude 192.168.5.1 - 127.

Jon

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