Earlier output below:
R3#show ip mroute 239.1.1.1
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 for MSDP Advertisement,
U - URD, I - Received Source Specific Host Report,
Z - Multicast Tunnel, z - MDT-data group sender,
Y - Joined MDT-data group, y - Sending to MDT-data group
Outgoing interface flags: H - Hardware switched, A - Assert winner
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 239.1.1.1), 00:04:07/00:03:19, RP 1.1.1.1, flags: BC
**Bidir-Upstream: FastEthernet0/0**, RPF nbr 192.168.13.1
**Outgoing interface list**:
**FastEthernet0/0, Bidir-Upstream/Sparse**, 00:04:07/00:00:00
**FastEthernet0/1, Forward/Sparse**, 00:04:07/00:03:19
Above you see that the FastEthernet0/0 interface is the upstream (towards the RP) and FastEthernet0/1 is the outgoing interface (towards R5). Now we will configure R4 to join the 239.1.1.1 multicast group as well so that they can communicate with each other: