Now it's time to look at PIM packets for IPv6 PIM SSM.
There's very little different here between IPv4 and IPv6,
the main thing is the SSM group range and the protocol
used; MLDv2 uses ICMPv6 to communicate.
Though delving into it is beyond the scope of this course,
ICMPv6 is used pretty flexibly for many IPv6 control plane applications.
The MLDv2 report is sent from the receiver to
request a PIM SSM group and source.
The information contained in the report is nearly identical to the IGMPv3
format and IPv4 because MLDv2 is just IGMPv3 for IPv6.
The report is sent to the ALL‑MLDv2‑ROUTERS group and
includes/excludes sources and groups.
Notice the link local groups are listed as Exclude,
but list 0 sources; this is the same as in any source
report in both IGMPv3 and MLDv2.
For our SSM group, we have it set to Include with one source,
which is the source we specifically requested in the configuration.
This PIM joins is from the last‑hop router where it converted the
MLDv2 report into a source tree join, the Upstream‑neighbor is the
designated router on the link, and the PIM join requests a group and
source just like the MLDv2 report. PIM SSM leverages the sparse mode
model rather than flooding because there's no need to inform the
routers of the source.
The receiver already knows what sources it wants to
subscribe to, and the PIM routers just need to resolve the
path to it using the Unicast best path.
In this module,
we discussed the following, a recap of the basic operation of PIM SSM, we saw a
demonstration of source‑specific multicast in action, next,
we looked at the packets that matter for source‑specific multicast, MLDv2 and the PIM Join/Prune.