Re: IGMPv3 merging of pending SLC records

On Thu, Jul 16, 2009 at 3:55 PM, Subrata Sa<[email protected]> wrote:
> Hello,
>
> This is regarding IGMPv3 host side behavior on merging of pending
> Source-List-Change (SLC) records.
>
My theoretical i.e. IPMulticastListen() calls (2, 3) given below are
misleading - please ignore them. I'm giving actual user API i.e.
setsockopt() calls below.

> In the example below, two SLC requests of opposite types (block,
> unblock) are made *when previous Filter-Mode-Change (FMC) record is in
> retransmission state*. I understand that the SLC records should be
> scheduled later. Question is how the SLC records should be merged? I'm
> thinking that both (BLOCK, ALLOW) SLC records be sent as given in (5)
> below. What do you think? Am I missing something?
>
> 1. Call IPMulticastListen(s, i, G, EXCLUDE, {})
setsockopt(s, .., IP_ADD_MEMBERSHIP, {G, i}), ..)

> -> Stack sends TO_EX(G, {}) FMC record (R1)
> -> State-change timer (T1) is started for retransmission
>
> 2. Before T1 expires, call IPMulticastListen(s, i, G, EXCLUDE, {a})
> i.e. block source
setsockopt(s, .., IP_BLOCK_SOURCE, {G, a, i}, ..)

> -> This SLC record is scheduled later as FMC record retransmission is
> pending (see reference A given below)
>
> 3. Before T1 expires, call IPMulticastListen(s, i, G, INCLUDE, {a})
> i.e. unblock source
setsockopt(s, .., IP_UNBLOCK_SOURCE, {G, a, i}, ..)

> -> This SLC record is also scheduled later as FMC record
> retransmission is pending (see A below)
>
> 4. Now T1 expires
> -> FMC record TO_EX(G, {}) is retransmitted (R2)
> -> As SLC records are pending, state-change timer (T2) is scheduled
>
> 5. Now T2 expires
> -> BLOCK(G, {a}), ALLOW(G, {a}) SLC records are sent (R3)
> -> State-change timer (T3) is started
>
> 6. Now T3 expires
> -> R3 is retransmitted (R4)
>
> --
> Reference A) RFC 3376 section 5.1, page 21:
>
> "
> If the interface reception-state change that triggers the new report
> is a filter-mode change, then the next [Robustness Variable] State-
> Change Reports will include a Filter-Mode-Change record. This
> applies even if any number of source-list changes occur in that
> period.
> "
>
Indranil, Kawaguchi, thanks for your response.

-Subrata Sa