netdev - RE: (usagi-users 04056) Re: ping6 is sent out from wrong interface

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Date:	Wed, 25 Jun 2008 13:26:06 +0200
From:	"Fey Marcus" <Fey@...g.de>
To:	"Naohiro Ooiwa" <nooiwa@...aclelinux.com>
Cc:	<usagi-users@...linux-ipv6.org>,
	YOSHIFUJI Hideaki / 吉藤英明 
	<yoshfuji@...ux-ipv6.org>, <netdev@...r.kernel.org>,
	<usagi-users@...ux-ipv6.org>
Subject: RE: (usagi-users 04056) Re: ping6 is sent out from wrong interface

Hi Naohiro,

>
>Hi Marcus
>
>Thank you for your quick reply.
>
>> It's due to routing.
>
>For the reason of selecting 'eth0', I agree.
>But, I think the device is specified before looking up the 
>routing table in this case.

Well, ping's man page reads: 
---
       -I interface address
              Set source address to specified interface  address.  Argument
              may  be  numeric  IP  address or name of device. When pinging
              IPv6 link-local address this option is required.
---

So you only set the address, not the interface to be used for sending.

>
>> ...with eth0 being preferred over eth1 for multicast packets.
>> You could add a dedicated route for ff02::/16 to make the 
>kernel output the packet via eth1.
>
>This works when using only "eth1" for multicasts.
>When multiple I/Fs are connected to separate networks, this 
>scheme requires changing the route every time a user need to 
>send ping to different network.
>

Ok, my proposition was a bit too general. It would probably be better to set up routes for the exact addresses. So in your case to ff02::1. 

Of course, if you wish to send the same packet via several interfaces within a short time, this would still result in adding and deleting the routes over and over again.

>I think kernel can solve this problem better.
>

I don't think this would be intended....


Bye,

Marcus
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