[ELDK] R: ARP Messages

Luigi Rizzi rizzi at algorab.com
Wed Nov 17 17:49:24 CET 2010

Hi Detlev,Stefano,

yes I really appreciate this mailing list! (and sorry if some questions are
not too much ELDK related...)

Well, Module interfaces and sniffer are connected to the same Ethernet HUB,
in this way the sniffer can see every input/output packet from Eth1 and
So, All my test were done NOT on two physical separated network. 

Stefano, are you sure about the fact that is not allowed to have both
interfaces sharing the same segment?

Anyway, there's in your opinion a workaround to avoid this double ARP

Best Regards,


-----Messaggio originale-----
Da: Detlev Zundel [mailto:dzu at denx.de] 
Inviato: mercoledì 17 novembre 2010 13.29
A: Luigi Rizzi
Cc: eldk at lists.denx.de
Oggetto: Re: [ELDK] ARP Messages

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:12:02       CompaqHp        ARP is at

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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