Auto-RP uses 2 multicast addresses to advertise the RP and the mapping information which are 224.0.1.39 and 224.0.1.40. It is operating in a sparse mode. However, there is a issue in the sense that all PIM routers need to join these 2 multicast groups in order to receive the RP announcement information. We encounter this problem by this followings.
- PIM sparse-dense mode : in this mode the router will act as if it is in dense mode at first. Then it moves back to sparse mode. Therefore, it will learn the 224.0.1.39 and 224.0.1.40 when it is in dense mode.
- Autorp-listener: This command will be configured at the global configuration. It allows only 2 multicast group which are 224.0.1.39 and 224.0.140 to to flood out to all PIM routers. It helps increase efficiency then flooding all multicast group to all routers at once like PIM sparse-dense mode does.
Example Configuration
Explanation
- Multicast source of 239.1.1.1 is located at R1 loopback interface with source address of 1.1.1.1
- Configure Auto-RP at R2 with RP announce at 2.2.2.2
- Configure the mapping agent at R2.
- R3 is a receiver of 239.1.1.1 multicast group.
Configuration
R2
ip pim send-rp-announce Loopback0 scope 5
ip pim send-rp-discovery scope 5
!
R3
ip multicast-routing
interface FastEthernet0/0
ip address 192.168.2.2 255.255.255.0
ip igmp join-group 239.1.1.1
duplex auto
speed auto
!
Debug output
*Mar 1 00:32:00.015: PIM(0): check pim_rp_announce 1
*Mar 1 00:32:00.015: PIM(0): send rp announce
*Mar 1 00:32:14.283: PIM(0): Send RP-reachability for 239.1.1.1 on FastEthernet0/1
*Mar 1 00:32:24.083: PIM(0): Building Periodic (*,G) Join / (S,G,RP-bit) Prune message for 239.1.1.1
*Mar 1 00:32:28.999: PIM(0): Received v2 Join/Prune on FastEthernet0/1 from 192.168.2.2, to us
*Mar 1 00:32:29.003: PIM(0): Join-list: (*, 239.1.1.1), RPT-bit set, WC-bit set, S-bit set
*Mar 1 00:32:29.003: PIM(0): Update FastEthernet0/1/192.168.2.2 to (*, 239.1.1.1), Forward state, by PIM *G Join
Verify
R3
show ip mroute
(*, 239.1.1.1), 00:30:14/00:02:25, RP 2.2.2.2, flags: SP
Incoming interface: FastEthernet0/0, RPF nbr 192.168.2.1
Outgoing interface list: Null
When R3 joined the 239.1.1.1 multicast group
R3 Join 239.1.1.1
ip igmp join-group 239.1.1.1
(*, 239.1.1.1), 00:25:13/00:02:27, RP 2.2.2.2, flags: SJPCL
Incoming interface: FastEthernet0/0, RPF nbr 192.168.2.1
Outgoing interface list: Null
R3 received the traffic from R1 lo0 (multicast source)
R3#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,
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), 00:26:20/stopped, RP 2.2.2.2, flags: SJPCL
Incoming interface: FastEthernet0/0, RPF nbr 192.168.2.1
Outgoing interface list: Null
(1.1.1.1, 239.1.1.1), 00:00:16/00:02:48, flags: PLTX
Incoming interface: FastEthernet0/0, RPF nbr 192.168.2.1
Outgoing interface list: Null
(192.168.1.1, 239.1.1.1), 00:00:16/00:02:48, flags: PLTX
Incoming interface: FastEthernet0/0, RPF nbr 192.168.2.1
Outgoing interface list: Null
(*, 224.0.1.39), 00:34:11/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, 00:34:11/00:00:00
(2.2.2.2, 224.0.1.39), 00:00:53/00:02:06, flags: PTX
Incoming interface: FastEthernet0/0, RPF nbr 192.168.2.1
Outgoing interface list: Null
(*, 224.0.1.40), 00:35:42/stopped, RP 0.0.0.0, flags: DCL
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/0, Forward/Sparse-Dense, 00:35:42/00:00:00
(192.168.2.1, 224.0.1.40), 00:30:12/00:02:37, flags: PLT
Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0
Outgoing interface list: Null
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