MULTICAST TROUBLESHOOTING GUIDE

Multicast troubleshooting is very different from unicast troubleshooting as you will have to think

backward in this one. What I mean to say is that to troubleshoot multicast RPF check plays a big role.

In Multicast check to following things to troubleshoot

1.) Every router has multicast-routing activated.

2.) Every participating port has Dense-Mode/Sparse-Mode is activated.

3.) If Sparse-Mode is used then every router knows about the RP by means or Static/Auto-

RP/BSR.

4.) Check PIM neighborship with other directly connected routers is up.

5.) Check for any filtering (rp-announce-filter, accept-rp, accept-register, multicast-boundary,

bsr-border, scope command in RP/MA/BSR configuration)

6.) traceroute the reverse path towards the source.

To check the above things use the following :

For Points 1, 2 and 3 => sh running-config | inc multicast|pim|interface|igmp

3.) For point 3 this can also be used : "show ip pim rp mapping"

4.) show ip pim neighbors

5.) show running-config | inc rp|boundary|bsr|scope

6.) mtrace

APART FROM the above commands, IF MSDP is used then check the following as well :

1.) The routers becoming MSDP peers have correct msdp command

2.) The IP addresses used in the msdp command are reachable.

3.) Check whether MSDP neighborship is up or not.

4.) any sa-cache filter

To check the above use following commands :

1.) sh run | inc msdp

2.) ping source

3.) sh ip msdp summary

4.) sh run | inc filter

NOTE : Remember in MSDP two organization connects over BGP. If BGP is only configured with unicast

address-family or no address-family then BGP routers use UNICAST ROUTING TABLE for RPF CHECK.

But if address-family multicast is used then MULTICAST BGP TABLE is checked first for RPF

CHECK.

IF BGP is configured with multicast address-family then you can check the routes you received in

multicast BGP table by the following command :

show bgp ipv4 multicast [summary]

* summary keyword will show the Multicast neighbors.

ARPIT PANDIT