avoid ip forward replaces the source MAC address

avoid ip forward replaces the source MAC address

[Elvis Yoan Tamayo Mollares]

hi list, during ip forwarding process, the kernel replace the source MAC 
address of the package it received with my own MAC address.. My question 
is: Is there any way to avoid this behavior?
Regards.

avoid ip forward replaces the source MAC address

[John Mahoney]

On Tue, Feb 1, 2011 at 2:27 PM, Elvis Yoan Tamayo Mollares
<etmoyares@grm.uci.cu> wrote:
> hi list, during ip forwarding process, the kernel replace the source MAC
> address of the package it received with my own MAC address.. My question
> is: Is there any way to avoid this behavior?

That is what routing does at the ip layer.  You may be able to
accomplish this by bridging the two ports together so that the traffic
is handled at layer 2.


--
John

avoid ip forward replaces the source MAC address

[Christophe Aeschlimann]

On 01.02.2011 20:39, John Mahoney wrote:
> On Tue, Feb 1, 2011 at 2:27 PM, Elvis Yoan Tamayo Mollares
> <etmoyares@grm.uci.cu> wrote:
>> hi list, during ip forwarding process, the kernel replace the source MAC
>> address of the package it received with my own MAC address.. My question
>> is: Is there any way to avoid this behavior?
> 
> That is what routing does at the ip layer.  You may be able to
> accomplish this by bridging the two ports together so that the traffic
> is handled at layer 2.


Indeed, have a look at :

http://www.linuxfoundation.org/collaborate/workgroups/networking/bridge

> --
> John

-- 
Christophe Aeschlimann

Embedded Software Engineer

ACN Advanced Communications Networks S.A.

Rue du Puits-Godet 8a
2000 Neuch?tel, Switzerland

T?l. +41 32 724 74 31

c.aeschlimann at acn-group.ch

avoid ip forward replaces the source MAC address

[John Mahoney]

On Tue, Feb 1, 2011 at 2:39 PM, John Mahoney <jmahoney@waav.com> wrote:
> On Tue, Feb 1, 2011 at 2:27 PM, Elvis Yoan Tamayo Mollares
> <etmoyares@grm.uci.cu> wrote:
>> hi list, during ip forwarding process, the kernel replace the source MAC
>> address of the package it received with my own MAC address.. My question
>> is: Is there any way to avoid this behavior?
>
> That is what routing does at the ip layer. ?You may be able to
> accomplish this by bridging the two ports together so that the traffic
> is handled at layer 2.

As a side note, looking at the iptables target:
 -m mac --mac-source XX:XX:XX:XX:XX:XX [1]

and the kernel code for that module (net/netfilter/xt_mac.c) it
appears that the src MAC address is saved in the sk_buff and is still
accessible in the PREROUTING, INPUT, and FORWARD chains via
eth_hdr(skb)->h_source.

I do not know if that helps.  I guess my point is my first answer was
the logical one, but it may be possible if you think outside the box.

--
John

[1]http://www.faqs.org/docs/iptables/matches.html#TABLE.MACMATCH

avoid ip forward replaces the source MAC address

[Bernd Petrovitsch]

On Die, 2011-02-01 at 14:27 -0500, Elvis Yoan Tamayo Mollares wrote: 
> hi list, during ip forwarding process, the kernel replace the source MAC 
> address of the package it received with my own MAC address.. My question 
> is: Is there any way to avoid this behavior?

Do not route (on IP-level/OSI layer 3) but switch only (on MAC level/OSI
layer 2).
Of course that has other implications and can't be done always ...

Bernd
-- 
Bernd Petrovitsch                  Email : bernd at petrovitsch.priv.at
                     LUGA : http://www.luga.at