netdev - Re: IPv6 multicast forwarding

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Message-ID: <50a66e370810240606ncb3dcd6gc949b734b1dcf488@mail.gmail.com>
Date:	Fri, 24 Oct 2008 09:06:49 -0400
From:	"Todd Hayton" <todd.hayton@...il.com>
To:	"Pekka Savola" <pekkas@...core.fi>
Cc:	"Alejandro Riveira Fernández" <ariveira@...il.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: IPv6 multicast forwarding

On Fri, Oct 24, 2008 at 6:12 AM, Pekka Savola <pekkas@...core.fi> wrote:
> On Fri, 24 Oct 2008, Alejandro Riveira Fernández wrote:
>>>
>>> Let me apologize in advance for the length of this message - it is long!
>>>
>>> I'm trying to test out IPv6 multicast forwarding on a 2.6.26 kernel
>>> and I'm getting some strange values for the upcall messages from the
>>> kernel. My code is below, but to give an overview, my setup is as
>>> follows:
>>>
>>>    sender ------ ff15::1 -----> [eth1] linux 2.6.26 [eth0] ------> ...
>
> Maybe this isn't the bug you're looking for but you shouldn't be using ff1x
> multicast addresses in a test like this; ff1x means that the multicast group
> is of "interface-local scope" and it isn't useful for multicast forwarding.
>  So the kernel might be correct in not installing multicast forwarding state
> for a group address like this (but if it's a conscious decision, maybe the
> failure mode should be better).  See S 2.7 of RFC4291.
>

Hey there, thanks for the response! I may be misinterpreting the RFC
but I thought ff15::1 was a site-local address. As in I break down
ff15::1 as follows -

0xff : identifies the address as multicast
0x15 : 4-bits flags and 4-bits scope where
  flags = 0x1 meaning that the T bit is set as this address is not a
permanently assigned address
  scope = 0x5 indicating site-local scope

Todd H


> --
> Pekka Savola                 "You each name yourselves king, yet the
> Netcore Oy                    kingdom bleeds."
> Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings
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