From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Fri Sep 24 2004 - 06:16:16 GMT-3
Only the first message from the client ("Hey, I need an address!!!") is
broadcasted (and thus relayed by the helper).
That message can be answered by many DHCP servers ("here you have x.x.x.x").
The client has to pick one of the offers and confirm ("I'll take it").
This has to go only to the selected server, which the server replies("ok").
Afterwards, when renewing, client should contact the original server for
renewal, no point in contacting anyone else...
Michael Snyder wrote:
> I got a production network and I was troubleshooting and problem with
> some win98 pc's. It's got about 110 win2000/xp machines on it that
> don't have a problem with dhcp, but about 12 out of 30 win98 machines
> can't get a unicast dhcp renewal but can get new broadcast lease.
>
> Our thinking now is that it's just a patch problem.
>
> ------------------------------------------------------------------------
> ---
>
> But some sniffer captures brought up another question.
>
> (dhcp server x.x.10.2)-(x.x.10.1 router/ip helper)-(client pc's
> x.x.100.x)
>
> Server subnet .10/24 and client subnet of .100/24
>
> In the captures I saw the clients 0.0.0.0 request broadcast to
> 255.255.255.255 get answered by an x.x.10.1 direct unicast to the
> clients new ip on the x.x.100.x side.
>
> Now also the unicast renewals went to the x.x.10.2 and was answered by
> x.x.10.2
>
> I always assumed that all dhcp traffic would go to the address of the ip
> helper router, but it seems only the incoming client broadcasts are
> relayed by it, and everything else is direct unicast to/from the far
> subnet dhcp server.
>
> Does this sound right? I've read the rfc's but they aren't clear about
> what IP source addresses I should see using ip helper from the clients
> viewpoint.
>
> If anyone can share some expertise on what I should be seeing, it would
> be very helpful.
>
> Thanks in Advance,
>
> Michael Snyder
> Lead Network Engineer
> CCSP/DP, MCSE NT/2000
> Revolution Computer Systems
>
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-- Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
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