netdev - RE: source IP address for ARP requests

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Date:	Tue, 7 May 2013 20:15:36 +0200
From:	Lukas Tribus <luky-37@...mail.com>
To:	Michael Tokarev <mjt@....msk.ru>, netdev <netdev@...r.kernel.org>
Subject: RE: source IP address for ARP requests

>  eth0  10.0.0.1/32
>  eth1  192.168.1.1/24
>  route add 10.0.0.2 dev eth1 src 10.0.0.1
> 
> namely, so that just one ip address is available
> on an "unrelated" subnet, with "our" address taken
> from another interface.
> 
> With this config, ARPs for 10.0.0.2 are sent to eth1
> with source address of 192.168.1.1, even if "src"
> is configured for the route in question:
> 
>  9:28:46.220680 ARP, Request who-has 10.0.0.2 tell
>                      192.168.1.1, length 28
> 
> Is that right, or should the host send ARP requests
> with src=10.0.0.1?

I suspect you cannot change the behavior of layer 2 discovery
protocols by configuring a certain layer 3 parameter (a route +
"src").

Also from an ARP perspective, this is imho correct behavior, because
10.0.0.2 should learn "sender hardware address" and "sender protocol
address" from the ARP _request_ and add them to its own ARP table -
without an additional ARP request. 10.0.0.2 is connected to eth1, so
only mac and ip address of eth1 counts in this case (= 192.168.1.1).

Regards,
Lukas 		 	   		  --
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