Hi,
Again, issues with multicast :)
I have the following topology:
http://i445.photobucket.com/albums/qq178/kpjungle/M-cast-topology.jpg,
When looking at this topology, and using PIM-SM in the entire network, I am
having a bit of trouble figuring out what R3 actually does.
(Group is 233.0.0.1 and soure is 100.0.0.2)
The steps I think i have under control are:
1) The source begins to send to RP.
2) R5 which is directly connected to the source, creates an (S,G) entry for
the source along with the mandatory (*,G) entry. The (S,G) entry has an
inc. interface toward the source.
3) RP receives the Register message, and creates an (*,G) and a (S,G)
entry. It still has no receivers, so the outgoing interface list of both is
NULL. Hence, it prunes both. But since source is still sending it must
maintain both entries.
4) Both R1 and R3 along the SPT path from RP -> Source, times out both
their (*,G) and (S,G) entries. All is good and dandy so far.
5) The receiver now tunes into the 233.0.0.1 stream.
6) R4 joins up the shared tree, all the way to the RP.
6) R4 also asks for an (S,G) join ((100.0.0.2, 233.0.0.1),
00:00:36/00:02:53, flags: JT) as shown by the J flag which should indicate
that this path was switched over from RPT to SPT.
7) Then with R3, It already has a SPT built, i would assume that
immediately it would send the RP-bit flag to R1 (toward the RP), and R1
would list this immediately point its (S,G) entry to the RP. However, the
(S,G) entry on R1 continues until times out, where it will then show that
is has sent the R flag (it wont time out), and it lists its Outgoing
Interface List as NULL.
What i dont get is what the R3 does when SPT switchover is enabled on R4,
and what happens when its not (ip pim spt-threshold infinity).. No matter
what, in my lab, R3 will use the SPT tree, even though with infinity i
expected data to flow from source to R5 to R3 to R1 to RP and then back
again to R3 and down to R4 and finally to receiver. I am assuming its
because the RPF check would fail on R3 when mpackets starts comming in a
non-RPF interface...
Generally confused :)
Maybe some brilliant person has some insights to this. Been reading over
the Developing IP Multicast networks multiple times...
Sincerely,
Kim Pedersen
