Subject: Re: Some comments regarding draft-ietf-ipngwg-default-addr-select-05.txt

From: Erik Nordmark <[email-masked]>
Date: Mon, 6 Aug 2001 23:15:20 +0200 (CEST)

> (At least for me) RFC 2461 is not very clear for multiple-interfaces
> cases, so the selection of the outgoing interface is implementation
> dependent.

RFC 2461 explicitly states that multihoming (which should have said
multi-interfaced hosts) is out of scope.

> Our (KAME's) implementation introduces the notion of "default
> interface", which should manually be specified by the user.  The
> kernel uses the default interface as the outgoing interface in this
> case.

Is the same default interface also the default for originating multicast
packets? Or do you have a separate default when no IPv6_MULTICAST_IF
is specified?

  Erik

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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Tue, 07 Aug 2001 10:00:05 +0900

>>>>> On Mon, 6 Aug 2001 23:15:20 +0200 (CEST), 
>>>>> Erik Nordmark <[email-masked]> said:

> multi-interfaced hosts) is out of scope.

Ah, correct.  I should've been clearer on this.

> packets?

Yes, sometimes, and indirectly.

Actually, when the kernel tries to send a multicast packet without any
hints on the outgoing interface, it looks up the routing table to
determine the outgoing interface.  Since the multicast destination
only matches the default route (unless there is a more specific
multicast route in the kernel), the kernel sends the packet to the
outgoing interface of the default route.

As I said before (in another thread?), if there is no default router,
and the default interface is specified, then the kernel installs a
"default route" to the interface to make neighbor cache for every
destination.  Consequently, multicasted packets without any hints will
be sent on the default interface.

If we have a default router, though, the packet will be sent to the
interface to the (currently preferred) default router, the interface
which may be different from the "default interface."

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]
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