Subject: [magma] MLDv2: Exclude mode

From: Erik Nordmark <[email-masked]>
Date: Tue, 18 Feb 2003 14:03:16 +0100 (CET)

There seems to be a significant inconsistency regarding
exclude mode. Section 5.2 has
       EXCLUDE (A)                B                   IS_IN (B-A)

Yet in section 4.2.12 the semantics of MODE_IS_INCLUDE is stated as
the listener is in include mode.

If there is a need to have a listener in exclude mode report an
include list of sources it would make sense to have that be a
separate report type (MODE_IS_EXCLUDE_WITH_INCLUDE_LIST or something
like that).

I've yet been unable to understand how the source timer works for
exclude mode.
Section 6.2.3 refers to the tables in 6.4 but I can't reverse engineer
the actual design from the rules in 6.4.
Is it possible to summarize these rules?

The text in 6.2.3 says:
   Source timers are treated differently when a router filter mode for a
   multicast address is EXCLUDE.  If a source record has a running timer
   it means that at least one system desires the source.  It should
   therefore be forwarded by some router on the network.  Appendix A
   describes the reasons for keeping state for sources that have been
   requested to be forwarded while in EXCLUDE state.
The above doesn't make sense since in exclude mode there isn't a source
record for every desired source. Instead there is a source record
(with timer=0) for every undesired source, right?
As I said elsewhere, having a separate include and exclude list
would make it easier to understand this.
But even with such a separation I can't understand how the exclude
list entries are managed - they are timed out when the multicast
address timer fires but are there other cases when they are removed?
There most be in order for the protocol to work.

   Erik

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