[c-nsp] UDP-helper problem

[Peter Rathlev]

On Wed, 2009-03-04 at 13:00 +0000, Michael Robson wrote:
> I have recently moved the routing of a subnet from an old sup2/msfc2  
> 6500 (Version 12.1(26)E8, RELEASE SOFTWARE (fc1)) to a newer sup3/ 
> msfc3 6500 (Version 12.2(18)SXF13, RELEASE SOFTWARE (fc1)). On the old  
> router the udp-helper command worked fine, but on the new router I can  
> see the DHCP address coming in but not the reply coming back and the  
> DHCP server isn't seeing the request arriving. Can anyone suggest why  
> this might have stopped working (it isn't an ACL or firewall issue as  
> there aren't any in the way) and I haven't turned _off_ any component  
> of udp-helper (i.e. using the ip forward-protocol command).
> 
> interface Vlan937
>   description XXXYYYZZZ
>   ip address w.x.y.z 255.255.255.192
>   ip helper-address a.b.c.d

AFAIK this forwarding requires the device to have "service dhcp", which
is default. Do you have "no service dhcp" defined maybe?

(I might have misunderstood this requirement though.)

We use this in many places for Sup720 SXF13 boxes, so it should work.

Another thing could be the DHCP server. If you know "by sniff" that the
packet doesn't arrive at the DHCP this is not relevant, but the DHCP
server would of course only reply if e.g. netmasks are the same.

Regards,
Peter