The information provided below is simply my study notes and not meant to be a full and complete resource on multicast troubleshooting. For more information please refer to the cisco website – www.cisco.com/en/US/tech/tk828/technologies_tech_note09186a0080094b55.shtml
This list of Multicast Troubleshooting Cisco Commands should help you find most problems relating to the troubleshooting section of the Cisco CCIE Lab exam.
The first task in any Multicast Troubleshooting task is to verify if Multicast is enabled and if the device has formed any pim neighbors.
- show ip pim interface
- sh ip pim neighbor
[stextbox id=”black”]R4#sh ip pim interface
Address Interface Ver/ Nbr Query DR DR
Mode Count Intvl Prior
192.168.1.1 Fa0/1 v2/S 1 30 1 18.104.22.168[/stextbox]
From this command you can see that PimV2 is enabled on the Fa0/1 interface
[stextbox id=”black”]R4#sh ip pim neigh
PIM Neighbor Table
Mode: B – Bidir Capable, DR – Designated Router, N – Default DR Priority,
P – Proxy Capable, S – State Refresh Capable, G – GenID Capable
Neighbor Interface Uptime/Expires Ver DR
192.168.1.2 Fa0/1 00:00:24/00:01:20 v2 1 / DR S P G
From this command you can see that router 4 has formed a PIM neighbor with a device with the IP of 192.168.1.2 out it’s Fa0/1 interface.
You need to do these 2 commands on all devices in the multicast network to verify if pim has been enabled on the interface and if a PIM neighbor has been formed.
Any missing interface commands of neighbors not up can be resolved at this stage
For Sparse-Mode you next have a lot of mechanisms for defining the RP, the following commands should assist with any Rendezvous Point configuration problems.
- debug ip pim auto-rp
- debug ip pim bsr
- debug ip mpacket
- sh ip pim rp-mapping
Debug ip pim auto-rp will show any problems with the group to auto-rp mapping
Debug ip mpacket will show the actual data plane forwarding for multicast, be aware however that only process switched traffic is going to show on the debug. You could go to the interface and type no ip mroute cache and this will turn process switching on and will allow you to see the debug output.
Show ip pim rp-mapping will tell you what mapping information you have for the RP, this needs to be checked on each device to ensure they all agree on the RP
So if you check sh ip pim rp-mapping and you do not see any output that would indicate a problem.
Check where the multicast boundary is and ensure the multicast packets are actually making it down to the end device.