In this demo,
we'll focus on how the multicast state tracking and traffic flow
differs from other implementations of PIM.
We'll start with multicast listener discovery and the PIM join at the last
hop router and then do the same from the first hop router.
We'll also look at the router providing the RP link and see how
traffic flows up and down the shared tree.
We did a similar demonstration in an IP before,
and this demonstration is mostly to show that the
IPv6 implementation is very similar.
First, we'll just verify that both ends are sending an MLD report.
The LHR is here getting the MLD report, and here's the PIM join.
The mroute table looks almost identical to the one in IPv4 except,
of course, that the addresses are IPv6.
There is a missing entry that existed in IPv4 though.
In the IPv4 version of BIDIR‑PIM,
the mroute table had a *,G entry for the whole multicast range and
then an individual PIM join for the specific group.
In IPv6,
the *,G for the whole range is missing because we don't need to
specify what groups we want to run in BiDir mode.
Only the RP itself is configured as a BiDir RP.
Remember that though the hostname says LHR and FHR,
that both routers have sources and receivers attached,
so they're really pulling double duty.
The multicast group on this router was requested via MLD,
now just to verify that it has been converted to a PIM join.
We do have the entry for the requested multicast group
based on having received an MLD report.
So let's look at the RP router now.
The PIM join for the multicast group has reached the RP from both sides.
Gig3 faces the LHR router and Gig1 faces the FHR router.
If only one side were requesting, this would have just one outgoing interface,
aside from the Bidir‑Upstream interface.
While Loopback100 is configured as the closest link to the phantom RP,
the PIM joins have come far enough.
Traffic forwarded from both sources up the Bidir‑Upstream
interface get to this router and then flow downward according
to the outgoing interface list.
As you can see, BIDIR‑PIM in IPv6 is almost identical to its IPv4 equivalent.
In the next section, we'll deep dive on the IPv6 BiDir packets and then wrap things up.