[ELDK] ARP Messages

Detlev Zundel dzu at denx.de
Wed Nov 17 13:28:48 CET 2010

Hi Luigi,

you seem to like our mailing list although the questions you have are
really not at all ELDK specific ;)

> I'm facing a strange behave on the ARP answers from my TQM885D module
> (U-boot 1.3.0-rc2 and kernel 2.4.25).  When I connect both Ethernet
> interfaces, for example configured as follow:
> Eth1:    IP           MAC 00:23:DE:CC:12:01
> Eth2:    IP         MAC 00:23:DE:CC:12:02
> If an ARP request arrives from the net the module sends two answers
> (from the two interfaces) with the same IP and different MACs.
> Here the packets I can see on the Ethernet sniffer:
> Source                         Destination       Protocol    Info
> ------------------------------------------------------------------------------------------------------------------------------------------------
> CompaqHp                   Broadcast         ARP         Who has
> 00:23:DE:CC:12:01       CompaqHp        ARP is at 00:23:DE:CC:12:01
> 00:23:DE:CC:12:02       CompaqHp        ARP is at 00:23:DE:CC:12:02

How is the sniffer connected?  To eth1 only?  Then it seems strange that
you actually see a packet with the MAC of eth2 there.  Somehow I do not
believe that without a special setup the MAC of eth2 is used for packets
on eth1 link...

> Anyone can tell me the reason why I'm getting also the second answer
> (of course a wrong answer) ?

The answer can only be given once we know your whole network setup,
i.e. what iptables do you have active, what routing tables do you have,
do you have a bridging setup active, does one of the interfaces do
proxy-arp, etc.  You need to provide all those informations before we
can help.


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