Subject: mboned: routingarch-06bis: proposed text in Section 2.7.2

From: Pekka Savola <[email-masked]>
Date: Tue, 7 Nov 2006 16:31:19 +0200 (EET)

Hi,

It's nice to see some discussion about the routingarch document.  You 
know, longer reviews would be even better... ;-)  But that aside, 
below is the new section 2.7.2 I'm proposing.  Edits:

 - GARP/GMRP, MRP/MMRP text update as suggested by Dan (note I didn't 
   remove the last sentence referring to RFC3488 because that still 
   seems to include useful information),

 - IP/MAC mapping phrasing suggestion made by Bert.  Personally I'd 
   rather have omitted 'However, this GMRP-IGMP association is beyond 
   the scope of GMRP.' because it isn't precluded either but kept it 
   unless others feel otherwise, and

 - Expand CGMP discussion a bit, because a lot of people seem to be 
   asking about it.  Please double-check this.

The first and last three paragraphs haven't been modified except for 
reference updates.

2.7.2.  Host/Router Flooding Reduction

   There are a number of techniques to help reduce flooding both from a
   router to hosts, and from a host to the routers (and other hosts).

   Cisco's proprietary CGMP [CGMP] provides a solution where the routers
   notify the switches, but also allows the switches to snoop IGMP
   packets to enable faster notification of hosts no longer wishing to
   receive a group.  Fast leave behaviour does not work very well with  
   IGMPv3.  Due to IGMP report suppression in IGMPv1 and IGMPv2,
   multicast is still flooded to ports which were once members of a
   group as long as there is at least one receiver on the link.
   Flooding restrictions are done based on multicast MAC addresses, and
   if IP/MAC multicast mappings overlap, host may receive multicast
   which is filtered out at the IP layer.  IPv6 is not supported.

   IEEE 802.1D-2004 specification describes Generic Attribute
   Registration Protocol (GARP), and GARP Multicast Registration
   Protocol (GMRP) [GMRP] is a link-layer multicast group application of
   GARP that notifies switches about MAC multicast group memberships.   
   If GMRP is used in conjunction with IP multicasts, then the GMRP     
   registration function would become associated with an IGMP "join."   
   However, this GMRP-IGMP association is beyond the scope of GMRP.     
   GMRP requires support at the host stack and it has not been widely   
   implemented.  Further, IEEE 802.1 considers GARP and GMRP obsolete   
   being replaced by Multiple Registration Protocol (MRP) and Multicast 
   Multiple Registration Protocol (MMRP) that are being specified in    
   IEEE 802.1ak [802.1ak].  MMRP is expected to be mainly used between  
   bridges.  Some further information about GARP/GMRP is also available 
   in Appendix B of [RFC3488].

   IGMP snooping [RFC4541] appears to be the most widely implemented
   technique.  IGMP snooping requires that the switches implement a 
   significant amount of IP-level packet inspection; this appears to be
   something that is difficult to get right, and often the upgrades are
   also a challenge.

   Snooping switches also need to identify the ports where routers
   reside and therefore where to flood the packets.  This can be  
   accomplished using Multicast Router Discovery protocol [RFC4286],
   looking at certain IGMP queries [RFC4541], looking at PIM Hello and
   possibly other messages, or by manual configuration.  An issue with
   PIM snooping at LANs is that PIM messages can't be turned off or   
   encrypted, leading to security issues
   [I-D.ietf-pim-lasthop-threats].

   IGMP proxying [RFC4605] is sometimes used either as a replacement of
   a multicast routing protocol on a small router, or to aggregate IGMP/
   MLD reports when used with IGMP snooping.

-- 
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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