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Status: Verified (1)

RFC 4605, "Internet Group Management Protocol (IGMP) / Multicast Listener Discovery (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", August 2006

Errata ID: 3285
Status: Verified
Type: Technical
Publication Format(s) : TEXT
Reported By: Jon Hak Song
Date Reported: 2012-07-14
Verifier Name: Brian Haberman
Date Verified: 2012-07-24

Section 3 says:

Note that this does not protect against an "upstream loop".  For
   example, see the figure below:


           LAN 1  --------------------------------------
                  Upstream |              | Downstream
                           A              B
                Downstream |              | Upstream
           LAN 2  --------------------------------------

   B will unconditionally forward packets from LAN 1 to LAN 2, and A
   will unconditionally forward packets from LAN 2 to LAN 1.  This will
   cause an upstream loop.  A multicast routing protocol that employs a
   tree building algorithm is required to resolve loops like this.

It should say:

Note that this does not protect against an "upstream loop".  For
   example, see the figure below:


           LAN 1  --------------------------------------
                  Upstream |              | Downstream
                           A              B
                Downstream |              | Upstream
           LAN 2  --------------------------------------

   B will unconditionally forward packets from LAN 2 to LAN 1, and A
   will unconditionally forward packets from LAN 1 to LAN 2.  This will
   cause an upstream loop.  A multicast routing protocol that employs a
   tree building algorithm is required to resolve loops like this.

Notes:

Multicast packets should be forwarded from Upstream to Downstream.

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