multicast drops

Unanswered Question
Sep 2nd, 2010
User Badges:

I am seeing currently seeing an issue where multicast traffic is not reaching client boxes at a particular location.  When I check the first router upstream from the client everything looks normal with the joins, but the multicast isn't getting that far.

(*,, 2d16h/00:02:53, RP, flags: DC
  Incoming interface: Null, RPF nbr
  Outgoing interface list:
    GigabitEthernet2/0, Forward/Sparse-Dense, 2d16h/00:00:00

IGMP Connected Group Membership
Group Address    Interface                Uptime    Expires   Last Reporter      GigabitEthernet0/0/0.605 2d16h     00:02:54

The traffic is getting dropped on the router upstream from the one shown above.  I can see they get dropped as "Other drops"...however, the OIF is not null, and there is no for what other reasons would they get dropped?

sh ip mroute

(,, 00:01:18/00:01:41, flags:
  Incoming interface: POS2/0, RPF nbr, Mroute
  Outgoing interface list:
    GigabitEthernet6/0, Forward/Sparse-Dense, 00:01:18/00:00:00

sh ip mroute count:

Group:, Source count: 1, Group pkt count: 0
  Source:, Forwarding: 0/0/0/0, Other: 2493/40/2453

Furthermore, when I send multicast from another source in the same subnet, to the same client box, it is succssful.

Group:, Source count: 2, Group pkt count: 3
  Source:, Forwarding: 3/1/32/0, Other: 4/1/0
  Source:, Forwarding: 0/0/0/0, Other: 3142/101/3041

One thing that I did notice is that the TTL is too low on the one that is dropping.  The application sending the multicast needs to bump the TTL up by 1.  However, I would not expect the traffic to get dropped on this router.  The traffic I think should get forwarded to the next router, where the TTL would then be 1, and get dropped there.  I'm going to bump up the TTL by 1 tonight, but was really just curious as to why it was being dropped like this.

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)


This Discussion