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Cisco Multicast Troubleshooting Tips.

Most of time multicast issue is related with Reverse Path Forwarding (RPF) issue

1. Check multicast configuration

- Make sure ' ip multicast-routing ' is enabled

- Verify multicast configuration on each interfaces

ex) Cisco_Multicast# show ip pim interface

2. Find out multicast route

- Private multicast route is normaly 239.0.0.0/8 range.

ex) 239.100.100.1   ( try ' show ip mroute ' )

- If you don't have one, create one (fake) using below command

Cisco_Multicast#conf t
Cisco_Multicast(config)# int fa0/1 ; wherever multicast server would be.
Cisco_Multicast(config-if)# ip igmp join-group 239.100.100.1
 

3. Find RP (if spare or spare-dense mode is being used)

- From running configuration or ' show ip mroute '

4. Check multicast routing table for multicast group IP

Cisco_Multicast# show ip mroute 239.100.100.1

IP Multicast Routing Table 
Flags: D - Dense, S - Sparse, 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 - Advertised via MSDP 
Timers: Uptime/Expires 
Interface state: Interface, Next-Hop or VCD, State/Mode 

(*, 239.100.100.1), 00:01:15/00:02:59, RP 10.10.10.1, flags: DJC 
  Incoming interface: VLAN 100, RPF nbr 20.20.20.1 
  Outgoing interface list: 
    Ethernet3/1, Forward/Sparse-Dense, 00:01:15/00:00:00 
    Ethernet3/2, Forward/Sparse-Dense, 00:00:58/00:00:00 

5. Check RPF information for RP (in this case 10.10.10.1)

Cisco_Multicast# show ip rp 10.10.10.1
RPF information for ? (10.10.10.1)
  RPF interface: Ethernet4/0
  RPF neighbor: ? (0.0.0.0)
  RPF route/mask: 10.10.10.1/32
  RPF type: unicast (static)
  RPF recursion count: 0
  Doing distance-preferred lookups across table

6. Check unicast routing table for RP

Cisco_Multicast# show ip route 10.10.10.1
Routing entry for 10.10.10.1/32
  Known via "static", distance 1, metric 0 (connected)
  Routing Descriptor Blocks:
  * directly connected, via Ethernet2/0
   Route metric is 0, traffic share count is 1

** Mismatching Multicast feed path and unicast route path.

- Cisco IOS® calculates the RPF interface in this way. Possible sources of RPF information are Unicast Routing Table, MBGP routing table, DVMRP routing table and Static Mroute table

1. Static mroutes
2. DVMRP routes
3. MBGP routes
4. Unicast routes

7. Applying static mroute

Cisco_Multicast(config)# ip mroute 10.10.10.1 255.255.255.255 Ethernet2/0

Cisco_Multicast# show ip rp 10.10.10.1
RPF information for ? (10.10.10.1)
  RPF interface: Ethernet2/0
  RPF neighbor: ? (0.0.0.0)
  RPF route/mask: 10.10.10.1/32
  RPF type: unicast (static)
  RPF recursion count: 0
  Doing distance-preferred lookups across table

8. Extra command

Cisco_Multicast# show ip mroute 239.100.100.1 count

Cisco_Multicast# debug ip mpacket 224.1.1.1

Cisco_Multicast# show ip igmp group

Cisco_Multicast# show ip pim rp 239.100.100.1

Cisco_Multicast# show ip pim rp map

Cisco_Multicast# show ip traffic

Cisco_Multicast#show ip mroute active ; To check whether the router recognizes any active traffic .

Ref. http://www.cisco.com/en/US/tech/tk828/technologies_tech_note09186a0080094b55.shtml