Multicast timer expires

Question

I've a multicast network for security cameras (multiple RPs, bsr, connectivity with OSPF). The problem is that the monitors sometimes stop receiving the video stream.

(10.0.0.1, 234.0.0.1), 00:10:11/00:00:24, flags: T
  Incoming interface: Vlan1, RPF nbr 10.0.1.1, RPF-MFD
  Outgoing interface list:
    GigabitEthernet0/0, Forward/Sparse, 00:10:11/00:03:24, H

I noticed that after the "expire" timer counts down and the Outgoing interface changes to "null". Soon after that the route disappears from "sho ip mroute".

Could you get me some info how this should work? In test environment the counter restarts before reach 2:30. Moreover, when I remove the IGMP join-group the "show ip mroute" entries immediately goes to "null" outgoing interface.

I'm wondering what is responsible for resetting expire counter.

Thanks in advance!

Answer 1

Normally the router will periodically send a membership query to destination 224.0.0.1 (all hosts multicast group address). Hosts that receive this message will respond with a IGMP membership report to tell the router that they are still interested in receiving the multicast traffic. When the router receives the membership report, it’s expiry timer will be refreshed.

Expiration can happen due to 2 reasons:

• When no hosts respond, the router knows that nobody is interested anymore in the multicast traffic and it will then remove the entry once the timer exceeds.

• Leave group messages: when a host no longer wants to listen to a multicast group address then it will report to the router that it has stopped listening.

Most probably you have an application issue on the server listening to the traffic and it is not sending IGMP messages correctly. You can solve the problem by adding ip igmp static group to the outgoing interface.