[rbridge] Consensus: Addition of "Other Multicast" bit to the Multicast RouterAttached Bits

[Eastlake III Donald-LDE008]

There seems to be plenty of support and almost no opposition to the
technical change below so we declare it to be the consensus of the TRILL
working group.

Donald & Erik

-----Original Message-----
From: rbridge-bounces at postel.org [mailto:rbridge-bounces at postel.org] On
Behalf Of Eastlake III Donald-LDE008
Sent: Saturday, July 28, 2007 11:43 PM
To: Rbridge at postel.org
Subject: [rbridge] Addition of "Other Multicast" bit to the Multicast
RouterAttached Bits

In the base protocol draft -05 there are two multicast router attachment
bits. The tentative consensus at the TRILL meeting last week was to add
a third bit so the situation would be as follows:

o There are 3 bits in TRILL IS-IS LSPs that appear per VLAN per Rbridge.
They are named "Other Multicast (OM)", "IPv4 attached multicast router
(MR4)", and "IPv6 attached multicast router (MR6)".

o When these bits are set, they cause all multicast frames for the
appropriate VLAN to be sent to the Rbridge with the bit on for IPv4
derived multicast (MR4), IPv6 derived multicast (MR6), or all other
multicast (OM). (Even if the MR4 or MR6 bit is off, multicast data
frames are still sent to the Rbridge if multicast listeners for that
data are reported by the Rbridge.)

o MR4 is set by an RBridge when it, as Designated Rbridge (DRB),
receives a native IGMP Query or IPv4 MRD Report on a port. (As per the
relevant RFCs, the bit times out and is cleared unless repeatedly set.)
This is an IGMP-snooping action. If an RBridge doesn't support this
IGMP-snooping action, it always sets this bit to 1.

o MR6 is set by an RBridge when it, as DRB, receives a native MLD Query
or IPv6 MRD Report on port. This is an MLD-snooping action. (As per the
relevant RFCs, the bit times out and is cleared unless repeatedly set.)
If an RBridge doesn't support this MLD-snooping action, it always sets
this bit to 1.

o OM can't be set by dynamic signaling since non-IPv4/IPv6 derived
multicast frames have no widely deployed signaling mechanism. It's value
is set by either configuration or deciding on a default setting.

o The recommendation is to default the 3 bits to {1,0,0} for
{OM,MR4,MR6} respectively for Rbridges that implement IP derived
multicast snooping. This causes all non-IPv4/IPv6 (other) multicast
frames to be flooded to such RBridges and snooping protocols can set the
MR4 and MR6 bits conditionally. For Rbridges that do not implement IP
derived multicast snooping, the bits should default to (1,1,1).

Thanks,
Donald

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