DHCPOFFER sent to wrong MAC?

[Jason Lixfeld]

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:

# netstat -rn
Routing tables

Internet:
Destination        Gateway            Flags    Refs      Use  Netif  
Expire
default            192.168.100.1      UGS         0   561688    xl0
127.0.0.1          127.0.0.1          UH          0   162223    lo0
192.168.100        link#1             UC          0        0    xl0
192.168.100.1      00:05:9b:bb:c6:a1  UHLW        2   123187     
xl0    951
192.168.100.2      00:03:e3:cc:e4:80  UHLW        1    15493     
xl0    681
192.168.100.10     00:50:04:d1:c9:f0  UHLW        1    57827    lo0
192.168.100.158    00:02:3f:8c:c2:3c  UHLW        1      303    xl0    
1024
192.168.100.190    00:12:3f:ca:e5:34  UHLW        1       95    xl0    
1045
192.168.100.192    00:11:24:1e:ef:4d  UHLW        1     2083     
xl0    477
# ifconfig xl0
xl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
         options=9<RXCSUM,VLAN_MTU>
         inet 192.168.100.10 netmask 0xffffff00 broadcast  
192.168.100.255
         ether 00:50:04:d1:c9:f0
         media: Ethernet autoselect (100baseTX <full-duplex>)
         status: active
#

> Simon