[rbridge] TRILL Header/Tag

[J. R. Rivers]

With IP multicast pruning in bridges, the traditional mode of operation
has been... if you don't know for sure, don't prune.  This is what
allows various implementations to be deployed in the face of no real
specification covering the functionality (and changes in IGMP versions
along the way).

JR
 

> -----Original Message-----
> From: rbridge-bounces at postel.org 
> [mailto:rbridge-bounces at postel.org] On Behalf Of James Carlson
> Sent: Thursday, June 28, 2007 11:49 AM
> To: Eastlake III Donald-LDE008
> Cc: rbridge at postel.org
> Subject: Re: [rbridge] TRILL Header/Tag
> 
> Eastlake III Donald-LDE008 writes:
> > For example, both 224.0.0.42 and 225.128.0.42 are valid 
> IPv4 multicast
> > addresses from which the same MAC address, namely 01-00-5E-00-00-2A,
> > would be derived. You would want to prune traffic to 
> 225.128.0.42 but
> > you can't validly prune traffic to 224.0.0.42 because, 
> according to RFC
> > 4541, hosts do not consistently issue IGMPs for IPv4 
> addresses in the
> > 224.0.0.0/24 range.
> 
> Yep; exactly.  224.0.0.0/24 is both "link-local" and "well-known" and
> thus expected to work right without the help or interference of
> multicast routers.  (Where, "right" means that all stations on the
> link can receive it.)
> 
> > I haven't studied all the IGMP stuff for different versions but, for
> > IGMP (and MLD), at best you have the problem in the 
> paragraph above and
> > at worst even the IP multicast address would be inadequate 
> and you would
> > have to look deeper into the frame to check the IP 
> protocol, etc., in
> > order to decide whether to prune just to branches with IP multicast
> > routers.
> 
> For IGMPv2, you'll need to look deeper, because the IGMP Report
> messages from hosts themselves are sent on the group address (RFC 2236
> section 9).  With IGMPv3, the Report messages are directed to a common
> multicast address (224.0.0.22; RFC 3376 section 4.2.14).
> 
> -- 
> James Carlson, Solaris Networking              
> <james.d.carlson at sun.com>
> Sun Microsystems / 1 Network Drive         71.232W   Vox +1 
> 781 442 2084
> MS UBUR02-212 / Burlington MA 01803-2757   42.496N   Fax +1 
> 781 442 1677
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