[rbridge] Consensus around MGROUP set of PDUs

[Linda Dunbar]

Does TRILL have different multicast addresses for different multicast
groups, like IEEE802.1Q does? Why need different PDU for different multicast
groups? 

Regards, Linda Dunbar



-----Original Message-----
From: rbridge-bounces at postel.org [mailto:rbridge-bounces at postel.org] On
Behalf Of Erik Nordmark
Sent: Friday, June 04, 2010 11:39 AM
To: Developing a hybrid router/bridge.
Subject: [rbridge] Consensus around MGROUP set of PDUs


Based on the recent discussion on the list, and not having found any
earlier discussion on the MGROUP set of PDUs on the TRILL WG mailing
list, it seems that there was never any TRILL WG discussion and
consensus about the need for or use of separate PDUs for multicast
membership.

The fact that there was some IS-IS WG discussion about this seems
unrelated, since the TRILL WG is the one to decide what they need from
IS-IS. And in the trill-protocol spec we don't specify any need for
additional PDU types for multicast.  In fact the document seems to talk
about TLVs and sub-TLVs in the regular LSP PDU:

4.2.4.4 TRILL LSP Information

    The information items in the TRILL IS-IS LSP that are mentioned
    elsewhere in this document are listed below. Unless an item is stated
    in the list below to be optional, it MUST be included. Other items
    MAY be included unless their inclusion is prohibited elsewhere in
    this document. The actual encoding of this information and the IS-IS
    Type or sub-Type values for any new IS-IS TLV or sub-TLV data
    elements are specified in a separate document [layer2].

Note that for the MTU testing in section 4.3.2 it is clear that the
expectation is that new IS-IS message types are needed.

Hence I conclude that the TRILL WG consensus has been to not require any 
new MGROUP PDU types.

If there is disagreement, or a need to revisit this, then I suggest the
proponents of MGROUP PDUs for TRILL make the case in the TRILL WG why
this would be required for TRILL's use of IS-IS. But that would be a
change from the current TRILL protocol specification.

    Erik

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