Clients keep sending DHCPDECLINE

[Tom Schmitt]

-------- Original-Nachricht --------
> Datum: Mon, 23 Aug 2010 09:28:08 +0200
> Von: moffe at zz9.dk
> An: Users of ISC DHCP <dhcp-users at lists.isc.org>
> Betreff: Re: Clients keep sending DHCPDECLINE

> Hi all
> 
> Could this be caused by a network loop? I also get multiple ARP replies
> in many cases like eg. this:
> 
> 06:21:43.585145 arp who-has 172.31.0.1 tell 172.16.0.2
> 06:21:43.585288 arp reply 172.31.0.1 is-at 00:23:df:f9:3d:74
> 06:21:43.585755 arp reply 172.31.0.1 is-at 00:23:df:f9:3d:74
> 06:21:43.586362 arp reply 172.31.0.1 is-at 00:23:df:f9:3d:74
> 

Yes, I do think that could be the source of your problems. If you have a problem in your routerconfiguration (like two HSRP-interfaces, both acting as active) or someone else in the subnet, acting as a router (maybe via wlan), then some traffic can easily getting multiplied.

This could explain the DHCPDECLINES:
The client is sending it's ARP request to see if someone has this IP already. Through the network-loop the client is receiving it's own ARP-request and interprete it in a form, that someone seems to claim this address, so it will be in use in short time. Ergo the client is sending the DHCPDECLINE, hoping to get an answer were nobody else is claiming the IP.

Tom.
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