Debugging Multicast Routing

Debugging gives you detailed information about the Protocol-Independent Multicast (PIM) data that your router sees on the network. With PIM data, you can select the types of debug data you want to observe, or you can choose to see all of it by only using the command at debug ip pim.

Router2>enable
Password:
Router2#debug ip pim ?
  atm      PIM ATM signalling activity
  auto-rp  Auto-RP
  bsr      PIM Candidate-RP/BSR activity
  df       PIM RP designated forwarder election activity
  hello    PIM Hello packets
  tag      PIM multicast tagswitching activity
  vrf      Select VPN Routing/Forwarding instance
  <cr>

Here is a sample of the type of data you see with the debug command. In the output, notice the join messages, RP information, and protocol version.

Router2>enable
Password:
Router2#debug ip pim
PIM debugging is on
*Mar 26 08:42:40.040: PIM(0): Building Periodic Join/Prune message for 224.0.1.40
*Mar 26 08:42:40.040: PIM(0): Insert (*,224.0.1.40) join in nbr 192.168.1.2's queue
*Mar 26 08:42:40.040: PIM(0): Insert (192.168.1.2,224.0.1.40) sgr prune in nbr 192.168.1.2's queue
*Mar 26 08:42:40.040: PIM(0): Building Join/Prune packet for nbr 192.168.1.2
*Mar 26 08:42:40.040: PIM(0): Adding v2 (192.168.1.2/32, 224.0.1.40), WC-bit, RPT-bit, S-bit Join
*Mar 26 08:42:40.040: PIM(0): Adding v2 (192.168.1.2/32, 224.0.1.40), RPT-bit, S-bit Prune
*Mar 26 08:42:40.040: PIM(0): Send v2 join/prune to 192.168.1.2 (FastEthernet0/0)
*Mar 26 08:42:45.292: PIM(0): Received RP-Reachable on FastEthernet0/0 from 192.168.1.2
*Mar 26 08:42:45.292: PIM(0): Received RP-Reachable on FastEthernet0/0 from 192.168.1.2
*Mar 26 08:42:45.296:      for group 224.0.1.40
*Mar 26 08:42:45.296: PIM(0): Update RP expiration timer (270 sec) for 224.0.1.40
*Mar 26 08:42:50.772: PIM(0): Send v2 Null Register to 192.168.1.2
*Mar 26 08:42:50.772: PIM(0): Received v2 Register-Stop on FastEthernet0/0 from 192.168.1.2
*Mar 26 08:42:50.776: PIM(0):   for source 0.0.0.0, group 0.0.0.0
*Mar 26 08:42:50.972: PIM(0): Building Periodic Join/Prune message for 239.192.152.143
*Mar 26 08:42:50.992: PIM(0): Received RP-Reachable on FastEthernet0/0 from 192.168.1.2
*Mar 26 08:42:50.992: PIM(0): Received RP-Reachable on FastEthernet0/0 from 192.168.1.2
*Mar 26 08:42:50.996:      for group 224.1.0.1
*Mar 26 08:42:53.776: PIM(0): Building Periodic Join/Prune message for 239.255.255.250
*Mar 26 08:42:55.776: PIM(0): Send v2 Data-header Register to 192.168.1.2 for 192.168.1.2, group 224.0.1.40
*Mar 26 08:42:55.780: PIM(0): Received v2 Register-Stop on FastEthernet0/0 from 192.168.1.2
*Mar 26 08:42:55.780: PIM(0):   for source 192.168.1.2, group 224.0.1.40
*Mar 26 08:42:55.780: PIM(0): Clear register flag to 192.168.1.2 for (192.168.1.2/32, 224.0.1.40)
*Mar 26 08:42:59.492: PIM(0): Received RP-Reachable on FastEthernet0/0 from 192.168.1.2
*Mar 26 08:42:59.492: PIM(0): Received RP-Reachable on FastEthernet0/0 from 192.168.1.2
*Mar 26 08:42:59.496:      for group 224.0.1.39
*Mar 26 08:42:59.496: PIM(0): Update RP expiration timer (270 sec) for 224.0.1.39
Router2#u all
All possible debugging has been turned off

As with the PIM debugging, you can selectively enable Internet Group Management Protocol (IGMP) for specific elements or for all IGMP debug data.

Router2>enable
Password:
Router2#debug ip igmp ?
  snooping  IGMP snooping activity
  vrf       Select VPN Routing/Forwarding instance
  <cr>

In the option for all debug information, notice that the type of information displayed includes protocol version, data requests received and from whom, and exclusion requests.

Router2>enable
Password:
Router2#debug ip igmp
IGMP debugging is on
*Mar 26 08:47:58.168: IGMP(0): Received v2 Query on FastEthernet0/0 from 192.168.1.2
*Mar 26 08:47:58.168: IGMP(0): Set report delay time to 1.2 seconds for 224.0.1.40 on FastEthernet0/0
*Mar 26 08:47:58.276: IGMP(0): Received v2 Report on FastEthernet0/0 from 192.168.1.104 for 224.0.0.251
*Mar 26 08:47:58.276: IGMP(0): Report has illegal group address 224.0.0.251
*Mar 26 08:47:59.712: IGMP(0): Received v2 Report on FastEthernet0/0 from 192.168.1.31 for 239.255.255.250
*Mar 26 08:47:59.712: IGMP(0): Received Group record for group 239.255.255.250, mode 2 from 192.168.1.31 for 0 sources
*Mar 26 08:47:59.712: IGMP(0): Updating EXCLUDE group timer for 239.255.255.250
*Mar 26 08:47:59.712: IGMP(0): MRT Add/Update FastEthernet0/0 for (*,239.255.255.250) by 0
*Mar 26 08:47:59.984: IGMP(0): Send v2 Report for 224.0.1.40 on FastEthernet0/0
*Mar 26 08:47:59.984: IGMP(0): Received v2 Report on FastEthernet0/0 from 192.168.1.240 for 224.0.1.40
Router2#u all
All possible debugging has been turned off

Finally, for Cisco Group Management Protocol (CGMP) data, you only have the option to see all the debug information for the protocol.

Router2>enable
Password:
Router2#debug ip cgmp

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Source:http://www.dummies.com/how-to/content/debugging-multicast-routing.html