Multicast (S, G) entry stays in mroute table even after source is long gone

[kollyjc]

What would cause a multicast (S,G) entry in our routers mroute table (Pim Sparse environment with static rp set) to still be present if that source was removed (device physically unplugged from network) long ago (2+ days)?

This is what we are seeing on router(t1b1) closest to source (X.X.179.212).

(*, 224.0.1.22), 1d23h/stopped, RP X.X.40.255, flags: SPF

  Incoming interface: GigabitEthernet2/0/1, RPF nbr X.X.42.85

  Outgoing interface list: Null

(X.X.179.212, 224.0.1.22), 00:00:52/00:02:37, flags: FT

  Incoming interface: Vlan270, RPF nbr 0.0.0.0, Registering

  Outgoing interface list:

    GigabitEthernet2/0/1, Forward/Sparse, 00:00:52/00:02:37

At this point the (S, G) entry stays in Registering state, and then is eventually removed after the 3:30 timer expires, but is then re-inserted shortly thereafter.  The process repeats over and over.  Manually clearing the route does not fix it either, it seems to always come back.  I don't understand how this is possible if the source has been physically removed from the network.

[Ton V Engelen]

Hi

as 224.0.1.22 is used for SLP:

SLP is a packet-oriented protocol. Most packets are transmitted using UDP, but TCP can also be used for the transmission of longer packets. Because of the potential unreliability of UDP, SLP repeats all multicasts several times in increasing intervals until an answer has been received. All devices are required to listen on port 427 for UDP packets, SAs and DAs should also listen for TCP on the same port. Multicasting is used extensively by SLP, especially by devices that join a network and need to find other devices.

it could be you are seeing the repeats as described here.