More than one ip-helper address on one interface

[surfbum99]

Hi,

Does anyone know if you can have more than one ip helper-address on the same inferface, if the ip helper-addresses go to different DHCP servers?

I always though you can only have one per interface, for example on a Cisco 7200 CMTS.

 

[KiscoKid]

You can define more than one helper address. I don't know if that's true for all IOS releases but it's certainly true for 12.3 onwards.

 

[surfbum99]

Manys, if you can they how does it work? Is it like round-robin?

e.g three of them

ip helper-address 192.168.5.5
ip helper-address 192.168.5.89
ip helper-address 192.168.5.144

Does it round-robin them?

 

[ADB100]

The router will send simultaneous copies of the broadcast (encapsulated and send as unicast) to each of the defined helpers. It doesn't round-robin them as far as I know from a process point of view, although obviously it must send them in some order since the interfaces operate effectively serially.

HTH

Andy

 

[surfbum99]

Interesting, but what if it gets replies from all three DHCP servers? How, what decides who wins, so to speak.

 

[KiscoKid]

I believe the first reply is the one the client listens too - all the others will get get dropped.

 

[jdeisenm]

We have redundant "QIP" DHCP servers from Lucent which replicate their dhcp database. There is one IP helper address on each vlan. Does anyone know of freeware that will do this?