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Example Topology:
Rendezvous Point: 10.104.0.140.
FortiGate configuration should enable the multicast routing and have the required multicast policy to allow multicast traffic.
- Once routers are configured with Sparse-Mode multicast PIM Hellos are sent by the multicast routers to address 224.0.0.13 to establish neighborship, the default interval is 30 sec which helps maintain the neighborship.
- If no PIM Hello is received before Hold time (default value is 105 sec) expires the neighborship is lost.
- Command to check Rendezvous Point mapping quickly. Confirm output with the configuration under:
show router multicast
- Check the IGMP Connected Group Membership. Once multicast receivers start sending the IGMPv2 JOIN or IGMPv2. Membership Report: The respective multicast address shows up in IGMP groups.
- The 'Last Reporter' is the IP of the last receiver that sent the IGMPv2 packet for the respective multicast group (234.5.6.8) via interface 'mgmt'.
- The multicast receivers will send the IGMPv2 Membership Report when they first join the multicast group and in response to multicast queries.
- FortiGate will use the route for RP in the unicast routing-table to form IGMP neighborship.
- The DR (Designated Router) is the router that will forward the PIM join message from the receiver to the RP (rendezvous point).
- If there is no route in the unicast, routing-table for the RP, then the multicast debug will show that it has failed to get the neighbor for the multicast group.
- Below is the expected debug when configuration is in place and multicast works. The debug shows IGMP is received followed by PIM-JOIN being sent to RP.
- Use the below debugs for spare-mode multicast;
diagnose debug disable
diagnose debug reset
diagnose ip router pim-sm all enable
diagnose ip router pim-sm level info
diagnose debug enable
- Capture a few minutes to stop:
diagnose debug disable
diagnose debug reset
- PIM JOIN packet sent by FortiGate-1101E to multicast address 224.0.0.13 as seen in Wireshark capture:
- PIM-SM debugs from FGT-B, which is the source/server-side Designated Router (DR) show that PIM JOIN/PRUNE has been received.
- In the output of the command:
get router info multicast pim sparse-mode next-hop
The next-hops for all the multicast receivers and source, and RP.
- In the output of the command:
diagnose ip multicast mroute
- The source for the respective multicast group.
Note:
PIM Sparse-mode only works in VRF=0. NFR has already been raised to support PIM Sparse-mode in multi-VRFs. Command to see if neighborship is active or not:
For sparse-mode:
get router info multicast pim sparse-mode neighbour
Example:
Get router info multicast pim sparse-mode neighbour
Neighbor Interface Uptime/Expires Ver DR
Address Priority/Mode
10.15.0.140 port16 01d03h17m/00:01:17 v2 1 /
If Fortinet TAC support is required, create a ticket: Technical Tip: How to create a ticket for Fortinet TAC
Attach the output of the following commands:
Diagnose commands to TAC:
show router multicast
diagnose ip multicast status
diagnose ip multicast mroute
get router info multicast pim sparse-mode neighbor
get router info multicast pim sparse-mode neighbour-detail
get router info multicast pim sparse-mode interface-detail
get router info multicast pim sparse-mode next-hop
get router info multicast pim sparse-mode table
get router info multicast pim sparse-mode rp-mapping
get router info multicast pim sparse-mode bsr-info
Debug:
diagnose debug disable
diagnose debug reset
diagnose ip router pim-sm all enable
diagnose ip router pim-sm level info
diagnose debug enable
Capture a few minutes to stop:
diagnose debug disable
diagnose debug reset
Related articles:
Technical Tip: How to troubleshoot IGMP and PIM Dense Mode issues
Technical Tip: FortiOS Multicast Resource List
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