Information Technology Reference
In-Depth Information
In the initial topology, two receivers are inactive, and there is a single inactive source. The
first device to join the multicast group is Receiver 1. However, the upstream router does not
know anything about the requested group. There is no source online, so no multicast traffic
has been flooded to the router to create state. Example 11-1 shows the multicast state for
the upstream router from Receiver 1.
Example 11-1
Multicast State on R7 for Group 224.1.1.1
R7#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), 00:00:15/00:02:46, RP 0.0.0.0, flags: DC
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
Serial2/0, Forward/Dense, 00:00:15/00:00:00
Ethernet0/0, Forward/Dense, 00:00:15/00:00:00
In Example 11-1, the multicast state information for group 224.1.1.1 indicates the existence
of the group with the (*,G) entry. However, the lack of an (S,G) means that this group has
no source. This means that the receiver has joined the group, but no source is online.
The source comes online, sending traffic to its upstream router. This traffic is flooded
through the network; Receiver 1 now receives the traffic stream. The flooded traffic is
shown in Figure 11-8.
The traffic is sent to several routers that have no downstream receivers, either directly or
indirectly. This traffic is pruned to ensure that traffic is forwarded down the tree to only
listening stations. However, state is maintained in all routers for the multicast group. The
PIM-DM pruning is shown in Figure 11-9.
