DHCPOFFER sent to wrong MAC?

[George C. Kaplan]

Jason Lixfeld wrote:
> On 18-Aug-06, at 12:18 PM, Simon Hobson wrote:
> 
> 
>>Jason Lixfeld wrote:
>>
>>>I have isc-dhcpd-3.0.4 installed via FreeBSD ports on a 6.1-RELEASE-
>>>p3 machine with a custom kernel.
>>>
>>>My dhcp server is at 00:50:04:d1:c9:f0
>>>My dhcp client is at 00:11:a0:02:67:36
>>>
>>>The dhcp server logs show constant discover/offer pairs, but the
>>>client does not respond with a request, etc...
>>>
>>>Aug 17 14:35:59 bubbles dhcpd: DHCPDISCOVER from 00:11:a0:02:67:36
>>>via xl0
>>>Aug 17 14:35:59 bubbles dhcpd: DHCPOFFER on 192.168.100.249 to
>>>00:11:a0:02:67:36 via xl0
>>>Aug 17 14:36:01 bubbles dhcpd: DHCPDISCOVER from 00:11:a0:02:67:36
>>>via xl0
>>>Aug 17 14:36:01 bubbles dhcpd: DHCPOFFER on 192.168.100.249 to
>>>00:11:a0:02:67:36 via xl0
>>>Aug 17 14:36:03 bubbles dhcpd: DHCPDISCOVER from 00:11:a0:02:67:36
>>>via xl0
>>>Aug 17 14:36:03 bubbles dhcpd: DHCPOFFER on 192.168.100.249 to
>>>00:11:a0:02:67:36 via xl0
>>>
>>>I span'd the port on my switch which the dhcp server is connected to,
>>>and ran ethereal on it and noticed this:
>>>
>>># Discover
>>><snip>
>>>Ethernet II, Src: VtechEng_02:67:36 (00:11:a0:02:67:36), Dst:
>>>Broadcast (ff:ff:ff:ff:ff:ff)
>>>     Destination: Broadcast (ff:ff:ff:ff:ff:ff)
>>>     Source: VtechEng_02:67:36 (00:11:a0:02:67:36)
>>></snip>
>>>
>>># Offer
>>><snip>
>>>Ethernet II, Src: 3com_d1:c9:f0 (00:50:04:d1:c9:f0), Dst:
>>>Cisco_bb:c6:a1 (00:05:9b:bb:c6:a1)
>>>     Destination: Cisco_bb:c6:a1 (00:05:9b:bb:c6:a1)
>>>     Source: 3com_d1:c9:f0 (00:50:04:d1:c9:f0)
>>></snip>
>>>
>>>It's sending the offer to the wrong MAC address.  00:05:9b:bb:c6:a1
>>>is the MAC address of my default gateway router.
>>>
>>>Is this a configuration glitch on my end or is something else wrong?
>>>All clients appear to be affected similarly.
>>
>>Just a stab in the dark, do you have a spurious routing table entry
>>directing 255.255.255.255 via the router ?
> 
> 
> No, no entry for 255.255.255.255:

A couple of things to check on the router:

- Is the netmask correct?
- Is proxy-ARP enabled?

-- 
George C. Kaplan                            gckaplan at ack.berkeley.edu
IST - Infrastructure Services               510-643-0496
University of California at Berkeley