[c-nsp] UDP-helper problem

[Michael Robson]

On 5 Mar 2009, at 10:24, Peter Rathlev wrote:

> 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.)
>
The DHCP is no on a router, but a linux server several hops away.



> 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.


The traffic doesn't arrive at the DHCP server.

  Thanks,


Michael
--