[c-nsp] HSRP and dhcp-relay question

[Phil Mayers]

On Sat, Dec 23, 2006 at 12:44:53PM +0100, Gert Doering wrote:
>Hi,
>
>On Sat, Dec 23, 2006 at 11:00:23AM +0200, Mihai Tanasescu wrote:
>> Because of the 2 ip helper-address statements I get 2 DHCP requests that 
>> are identical.
>
>Yes, unavoidable (<insert plea for 'make HSRP standby interface inactive
>regarding all other IP functions'>).

Yes and yes.

BE AWARE however, that I have seen some DHCP clients e.g. PXE ROMs take 
the gateway as the relay IP (which is the real IP) and not the virtual 
IP embedded in the DHCP gateway field.

If the client happens to receive the response from the non-master and 
that router has somehow compromised connectivity e.g. it has moved to a 
low-bandwidth wireless link then your DHCP client may experience 
problems.

This is not a cisco fault, though HSRP does make the fault show up.

>
>> Is there any way to make a single request happen and to have it 
>> forwarded with SRC IP == standby IP ?
>
>As far as I can tell, no.
>
>OTOH, in our own experience, this doesn't seem to to harm - we've run
>this with ISC DHCPD and with MacOS X Server DHCPD, and in both cases,
>both replies are identical, and the clients don't seem to mind.

It works just fine with every setup I've ever tried too.