Information Technology Reference
In-Depth Information
Example 11-5 shows the multicast state information for a router on the shared tree. R4 was
chosen because it is where the shared tree and the source tree diverge. The OIL is populated,
and the incoming interface is pointed back toward the RP. This state information is the
shared tree being built from the receiver to the RP, where the receiver is expecting to
rendezvous with a source.
Example 11-5
Shared Tree State Information for 224.1.1.1 on R4
R4#show ip mroute 224.1.1.1
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected,
L - Local, P - Pruned, R - RP-bit set, F - Register flag,
T - SPT-bit set, J - Join SPT, M - MSDP created entry,
X - Proxy Join Timer Running, A - Candidate MSDP Advertisement,
U - URD, I - Received Source Specific Host Report, Z - Multicast Tunnel
Y - Joined MDT-data group, y - Sending to MDT-data group
Outgoing interface flags: H - Hardware switched
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 224.1.1.1), 00:00:28/00:03:06, RP 10.1.1.2, flags: S
Incoming interface: Serial4/0, RPF nbr 10.2.1.10
Outgoing interface list:
Serial2/0, Forward/Sparse, 00:00:28/00:03:06
A source begins sending traffic to the multicast group. The first downstream router from the
multicast source registers with the RP. The RP receives the special Register message that is
sent via unicast, alerting it to the existence of a source. The Register message encapsulates
the arriving multicast packets to ensure that no multicast packets are dropped while the RP
is building the source tree to the source. The RP builds a source tree to the source. As soon
as traffic begins to flow down the source tree to the RP, the RP sends a Register Stop mes-
sage to end the registration process. At this point, the required MDTs for traffic delivery
form. Figure 11-14 shows the register process and the construction of the SPT from the RP
to the source. The traffic is sent from the RP down the shared tree to the receiver.
The MDT is shown in Figure 11-15.
