- 1. Enable ip multicast routing globally
- 2. Set nominated RP
- 3. Enable PIM mode (Dense, Sparse etc)
We’ll verify the neighbor relationships with show ip pim neighbor.
R1#show ip pim neighbor PIM Neighbor Table Neighbor Address Interface Uptime Expires Ver Mode 188.8.131.52 Serial0 00:00:37 00:01:37 v2 184.108.40.206 Serial0 00:00:40 00:01:35 v2
Ever wonder how you can test whether routers have correctly joined a multicast group? Here’s an old CCIE lab trick – ping the multicast IP address of the group with the extended ping command.
R1#ping Protocol [ip]: Target IP address: 220.127.116.11 Repeat count : 100 Datagram size : Timeout in seconds : Extended commands [n]: Sweep range of sizes [n]: Type escape sequence to abort. Sending 100, 100-byte ICMP Echos to 18.104.22.168, timeout is 2 seconds: ............................
R1’s pings to 22.214.171.124 are failing because there are no members of that multicast group. Let’s fix that by making R2 and R3 members.
R2(config)#int s0 R2(config-if)#ip igmp join-group 126.96.36.199 R3(config)#int s0 R3(config-if)#ip igmp join-group 188.8.131.52
Let’s take a look at the multicasting route table on R2 with show ip mroute
R2#show 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 Outgoing interface flags: H - Hardware switched Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 184.108.40.206), 00:07:40/00:00:00, RP 220.127.116.11, flags: SJPCL Incoming interface: Serial0, RPF nbr 18.104.22.168 Outgoing interface list: Null (*, 22.214.171.124), 00:04:16/00:00:00, RP 126.96.36.199, flags: SJPCLF Incoming interface: Serial0, RPF nbr 188.8.131.52 Outgoing interface list: Null (184.108.40.206, 220.127.116.11), 00:04:16/00:01:13, flags: PCLFT Incoming interface: Serial0, RPF nbr 0.0.0.0 Outgoing interface list: Null
This table is quite different from the IP routing table we’re used to..
Note that there are two entries for 18.104.22.168. The first is a “star, group” entry. The star (“*”) represents all source addresses, while the “group” indicates the destination multicast group address. This entry is usually referred to as *, G in Cisco documentation. The second entry is a “Source,Group” entry, usually abbreviated as S,G in technical documentation. The Source value is the actual source address of the group, while the Group is again the multicast group address itself.
When spoken, the G entry is called a “star comma G” entry; the S,G entry is called a “S comma G” entry.
Note the RPF neighbor entry 0.0.0.0 for the 22.214.171.124,126.96.36.199 entry. That will always be 0.0.0.0 when you’re running sparse mode, as we are here.
D - Dense Mode entry S - Sparse Mode entry C - Connected, referring a member of the group being on the directly connected network L - Local Router, meaning this router itself is a member of the group P - Pruned, indicates the route has been pruned. T - Shortest Path Tree, indicates packets have been received on the tree.
To test this configuration. We’ll send pings to 188.8.131.52 and see what the result is…
R1#ping Protocol [ip]: Target IP address: 184.108.40.206 Repeat count : Datagram size : Timeout in seconds : Extended commands [n]: Sweep range of sizes [n]: Type escape sequence to abort. Sending 1, 100-byte ICMP Echos to 220.127.116.11, timeout is 2 seconds: Reply to request 0 from 18.104.22.168, 116 ms Reply to request 0 from 22.214.171.124, 128 ms
Both downstream members of the multicast group 126.96.36.199 responded to the ping.
There are some other commands you can use to verify and troubleshoot multicasting, one being show ip pim interface
R1#show ip pim interface Address Interface Version/Mode Nbr Query DR Count Intvl 188.8.131.52 Serial0 v2/Sparse 2 30 184.108.40.206
Note the “DR” entry. On multiaccess segments like the one we’ve got ere, a PIM Designated Router will be elected. The router with the highest IP will be the DR. The DR election is really more for Ethernet segments with more than one router than for NBMA networks like this fame relay network. The PIM DR has two major responsibilities.
1. Send IGMP queries to the LAN
2. If Sparse Mode is running, transmit PIM join and register messages to the RP.
You can verify IGMP group memberships with show ip igmp groups.
R2#show ip igmp groups IGMP Connected Group Membership Group Address Interface Uptime Expires Last Reporter 220.127.116.11 Serial0 00:58:20 00:02:49 18.104.22.168 22.214.171.124 Serial0 00:52:13 00:02:46 126.96.36.199