IP Helper Address

[kwillacey]

I wanted to know if it was possible to have two ip helper-addresses on the same interface, one for a primary DHCP source on a windows box and a secondary source which is the router itself. It seems I can only have one address based on the command.

So is there any way that this can be done?

[royalblues]

Hi Friend,

You can have 2 helper on the same interface but it does not work as active and standby.

The DHCP discover will be forwarded to both the servers and the response will be forwarded back to the client.

The client choses a server and send the request.

If you want to achieve load balancing you should configure 50% of your scope on one server and the rest on another.

HTH, rate if it does

Narayan

[kwillacey]

Ok so what would me the command to accomplish this.

int e0

ip helper-address X.X.X.X

ip helper-address X.X.X.X

[Martin Parry]

Hi

It is possible to put multiple ip helper addresses on an interface. You can just enter the command twice adjusting the ip address you are pointing to in each instance.

interface FastEthernet0/0

no ip address

ip helper-address 192.168.1.1

ip helper-address 192.168.2.1

shutdown

duplex auto

speed auto

end

Hope this helps

Regards

Martin

[Richard Burts]

Kelvin

The previous posts have given good answers about configuring 2 ip helper-address commands. And it is correctly pointed out that if you have 2 helper-address commands then the DHCP request is forwarded to both and it does not function as a primary and a backup.

But I am curious about part of what you said in the original post which is that the second DHCP server was the router itself. If I understand correctly that the router to which the client is connected is configured with DHCP pool etc for the subnet on which the client is connected then you will not need the second helper-address command. If the router is configured with DHCP pool and receives the DHCP request it will respond without needing a helper address command. The helper-address command is only needed when the server is on a subnet that is different from the subnet the client is on.

HTH

Rick

[kwillacey]

I have a dhcp pool on the router but I want the server which is on another subnet to respond to the DHCP request. I only want the router to respond if for some reason the request cannot get to the DHCP server.

[Richard Burts]

Kelvin

I have never seen a router set up to only serve DHCP addresses if a remote server failed to respond and I believe that it can not be done that way on the router.

HTH

Rick

[a.hajhamad]

Hi Rick,

I i understood the original post, and also this is my question.

Can we add the ip helper-address to be as a primary to forward the DHCP packets to the HQ DHCP server, and if for any reason the WAN link goes down, the IOS "gateway" will take the responsibility to serve the clients DHCP requests?

I think we can achieve this maybe by delaying the IOS for the DHCP requests for let us say 10 seconds, i think during this period if the DHCP requests received by the DHCP server, it will anser these requests, if not "no WAN connection" the IOS will answer these requests!

Thanks in advance

Abd Alqader