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

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Message-ID: <48621B7E.5090600@miraclelinux.com>
Date:	Wed, 25 Jun 2008 19:18:38 +0900
From:	Naohiro Ooiwa <nooiwa@...aclelinux.com>
To:	Fey Marcus <Fey@...g.de>
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 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.

> ...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.

I think kernel can solve this problem better.


Regards,
Naohiro Ooiwa


Fey Marcus さんは書きました:
> Hi Naohiro,
> 
>> I'm not convinced yet.
>> I don't think it's correct that kernel or ping6 arbitrarily 
>> decides outgoing interface.
>>
>> Is this really an expected behaviour?
>> Could you explain to me the reason of it, too?
>>
>> I think the behavior should be similar to IPv4.
> 
> It's due to routing.
> 
> Your routing table shows this:
> ---
>     # route -A inet6
>     Kernel IPv6 routing table
>     Destination            Next Hop Flags Metric Ref    Use Iface
>     2001:2c0:418:1::/64    *        U     256    0        0 eth0
>     2001:2c0:418:2::/64    *        U     256    0        0 eth1
>     fe80::/64              *        U     256    0        0 eth0
>     fe80::/64              *        U     256    0        0 eth1
>     ::::::
>     2001:2c0:418:1::1/128  *        U     0      8        1 lo
>     2001:2c0:418:2::2/128  *        U     0      5        1 lo
>     ::::::
>     ff00::/8               *        U     256    0        0 eth0
>     ff00::/8               *        U     256    0        0 eth1
>     #
> ---
> 
> ...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.
> 
> Bye,
> 
> Marcus
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