I have a simple topology like this:
So, I have Auto-RP configured where R3 and R4 are RP and c-RP for the same group and R5 is mapping agent and R2 is just a PIM neighbor. R1 and R6 are multicast source and dest.
So, after the magic of the Auto-RP happens, I can see the mroute table correctly populated in R5 with the (S,G) for 224.0.1.39 (R3 and R4 RPs) and 224.0.1.40 for R5 (itself) for receiving RP mapping (see output below)
R5#sh ip pim rp mapping
PIM Group-to-RP Mappings
This system is an RP-mapping agent (Loopback0)
Group(s)
224.1.1.1/32 RP 3.3.3.3 (?), v2v1
Info source: 3.3.3.3 (?), elected via Auto-RP
Uptime: 00:09:35, expires: 00:02:08
R5#sh ip mroute
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, E - Extranet,
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,
G - Received BGP C-Mroute, g - Sent BGP C-Mroute,
Q - Received BGP S-A Route, q - Sent BGP S-A Route,
V - RD & Vector, v - Vector
Outgoing interface flags: H - Hardware switched, A - Assert winner
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 224.0.1.39), 00:06:12/stopped, RP 0.0.0.0, flags: DCL
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet1/0, Forward/Sparse-Dense, 00:06:12/stopped
FastEthernet0/1, Forward/Sparse-Dense, 00:06:12/stopped
FastEthernet0/0, Forward/Sparse-Dense, 00:06:12/stopped
Loopback0, Forward/Sparse-Dense, 00:06:12/stopped
(4.4.4.4, 224.0.1.39), 00:06:06/00:02:14, flags: LT
Incoming interface: FastEthernet1/0, RPF nbr 10.1.1.4
Outgoing interface list:
Loopback0, Forward/Sparse-Dense, 00:06:06/stopped
FastEthernet0/0, Forward/Sparse-Dense, 00:06:06/stopped
FastEthernet0/1, Forward/Sparse-Dense, 00:06:06/stopped
(3.3.3.3, 224.0.1.39), 00:06:12/00:02:07, flags: LT
Incoming interface: FastEthernet0/0, RPF nbr 35.1.1.3
Outgoing interface list:
Loopback0, Forward/Sparse-Dense, 00:06:12/stopped
FastEthernet0/1, Forward/Sparse-Dense, 00:06:12/stopped
FastEthernet1/0, Forward/Sparse-Dense, 00:06:12/stopped
(*, 224.0.1.40), 00:06:12/stopped, RP 0.0.0.0, flags: DCL
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet1/0, Forward/Sparse-Dense, 00:06:12/stopped
FastEthernet0/0, Forward/Sparse-Dense, 00:06:12/stopped
Loopback0, Forward/Sparse-Dense, 00:06:12/stopped
(5.5.5.5, 224.0.1.40), 00:05:40/00:02:16, flags: LT
Incoming interface: Loopback0, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/0, Forward/Sparse-Dense, 00:05:40/stopped
FastEthernet1/0, Forward/Sparse-Dense, 00:05:40/stopped
On R2, being a normal PIM Neighbor, I expected to see just and (S,G) for 224.0.1.40, however I see also entries for 224.0.1.39 as in R5. My understanding is that just mapping-agent join group for RP-announcement when the other PIN-Neighbors join just the RP-Discovery. Can you help me to understand this part?
R2#sh ip mroute
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, E - Extranet,
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,
G - Received BGP C-Mroute, g - Sent BGP C-Mroute,
Q - Received BGP S-A Route, q - Sent BGP S-A Route,
V - RD & Vector, v - Vector
Outgoing interface flags: H - Hardware switched, A - Assert winner
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 224.1.1.1), 00:12:56/00:03:09, RP 3.3.3.3, flags: S
Incoming interface: FastEthernet0/0, RPF nbr 23.1.1.3
Outgoing interface list:
FastEthernet0/1, Forward/Sparse-Dense, 00:12:56/00:03:09
(*, 224.0.1.39), 00:13:57/stopped, RP 0.0.0.0, flags: DC
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/0, Forward/Sparse-Dense, 00:13:28/stopped
FastEthernet0/1, Forward/Sparse-Dense, 00:13:28/stopped
FastEthernet1/0, Forward/Sparse-Dense, 00:13:57/stopped
(3.3.3.3, 224.0.1.39), 00:10:55/00:01:37, flags: T
Incoming interface: FastEthernet0/0, RPF nbr 23.1.1.3
Outgoing interface list:
FastEthernet1/0, Forward/Sparse-Dense, 00:10:55/stopped
FastEthernet0/1, Forward/Sparse-Dense, 00:10:55/stopped
(4.4.4.4, 224.0.1.39), 00:12:54/00:01:47, flags: T
Incoming interface: FastEthernet1/0, RPF nbr 10.1.1.4
Outgoing interface list:
FastEthernet0/1, Forward/Sparse-Dense, 00:12:54/stopped
FastEthernet0/0, Forward/Sparse-Dense, 00:12:54/stopped
(*, 224.0.1.40), 00:13:57/stopped, RP 0.0.0.0, flags: DCL
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
Loopback0, Forward/Sparse-Dense, 00:13:57/stopped
FastEthernet0/0, Forward/Sparse-Dense, 00:13:28/stopped
FastEthernet0/1, Forward/Sparse-Dense, 00:13:28/stopped
FastEthernet1/0, Forward/Sparse-Dense, 00:13:30/stopped
(5.5.5.5, 224.0.1.40), 00:12:56/00:02:27, flags: LT
Incoming interface: FastEthernet1/0, RPF nbr 10.1.1.5
Outgoing interface list:
Loopback0, Forward/Sparse-Dense, 00:12:56/stopped
FastEthernet0/1, Forward/Sparse-Dense, 00:12:56/stopped
FastEthernet0/0, Prune/Sparse-Dense, 00:02:30/00:00:29