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Webcast-Catalyst9k
New Member

VRRP (or HSRP) and ip helper address

Hi,

I have a fairly redundant network setup. For my clients, I use VRRP to get a redundant default gateway (2 routers, R1 and R2). This works fine.

As the clients use DHCP, I use an ip helper address to get to the DHCP server on a different subnet.

I have 2 DHCP servers, hence I use 2 ip helpers per interface, but that is not the issue.

The DHCP server software used is the native DHCP software on Win2k8Sp2.

I am wondering what happens, if I put helpers on both vrrp interfaces.

* Does this mean the DHCP gets 2 DHCP requests (one fromR1, the other from R2)?

* How does each DHCP server respond?

* As I have 2 DHCP servers, should I point thehelper on each router to a different server?  eg R1 -> helper to server 1, R2 -> helper to server2

* What issues can I expect in this setup?

Any insight/comment is appreciated!

Marcel

Everyone's tags (5)
2 REPLIES
New Member

VRRP (or HSRP) and ip helper address

Hi Marcel!!,

What kind of DHCP configuration do you have on the DHCP server? If you are using two DHCP servers, then there should be scope splitting configured (on the DHCP server).

80/20 scope splitting could be followed. This means primary server will lease 80% of IP addresses for particular subnet and secondary the remaining 20%.

The two scopes have complementary exclusion ranges so never will give the same IP address to different clients.

Regards.

New Member

VRRP (or HSRP) and ip helper address

For the 1st question I test this settings in a lab environement using the ip helper address on both router. The two router listen to DHCP request and forward it to the DHCP Server but only one request will complete and the other will remain in standby. The DHCP Server won't register an IP address for the second request.

This configuration works fine for me.

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