Date: Mon, 18 Jun 2007 18:49:54 +0100 From: "Bruce M. Simpson" <bms@incunabulum.net> To: Ian FREISLICH <ianf@clue.co.za> Cc: current@freebsd.org Subject: Re: Multicast problems Message-ID: <4676C5C2.9030900@incunabulum.net> In-Reply-To: <E1I0FdR-0000LI-SA@clue.co.za> References: <E1I0FdR-0000LI-SA@clue.co.za>
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Ian FREISLICH wrote:
> It looks like it just uses IP_ADD_MEMBERSHIP. HAVE_BSD_STRUCT_IP_MREQ_HACK
> is defined. I really don't know anything about how it should be
> doing this to say whether the above code is correct.
>
This is expected behaviour. The new code phases out the hack which this
define refers to, which is to encode 24 bits of an interface index in
0.0.0.0/8 (first 8 bits set to zero).
The reason why the hack was needed in the first place is because of how
the BSD INADDR_TO_IFP() lookup works with regards to unnumbered and
point-to-point interfaces, as described in UPDATING.
The issue with joining groups on INADDR_ANY is separate from this -- it
is related only insofaras code which still expects to abuse the RFC 1724
style behaviour (0.0.0.0/8) is going to end up with INADDR_TO_IFP
returning NULL, and will hit the same path. I would expect Quagga to
fail to add the group with EADDRNOTAVAIL.
There have been attempts to fix this in NetBSD differently, by changing
the lookup, however, I should point out that it still doesn't fix the
issue with unnumbered interfaces:
http://mail-index.netbsd.org/netbsd-bugs/1999/04/02/0001.html
I didn't roll a patch for Quagga as it's not part of the base system.
Making the required change shouldn't be difficult. It is probably easier
for the purposes of Quagga to use the Linux-derived ip_mreqn extension
to the IP_MULTICAST_IF ioctl for interface selection, as ospf should be
using a locally-scoped address (224.0.0.5 falls under the local
administrative scope 224.0.0.0/8) -- although the MCAST_JOIN_GROUP ioctl
is the one to use if one needs to bind to an interface by index and be
sure that it actually worked.
The patch for Rhyolite routed demonstrates both techniques. It is
available here:
http://people.freebsd.org/~bms/dump/routed.rfc3678.diff
Kind regards,
BMS
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