Let's say we have this sample output from a PIM DM router:
rtr-b>show ip mroute IP Multicast Routing Table Flags: D - Dense, S - Sparse, C - Connected, L - Local, P - Pruned file:///V|/[%20CISCO%20PRESS%20]/Ciscopress-Developing.Ip.Multicast.Networks/di10ch10.htm (18 of 30)09/12/2003 01:11:54 Using PIM Dense Mode R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, 188.8.131.52), 00:00:12/00:00:00, RP 0.0.0.0, flags: D Incoming interface: Null, RPF nbr 0.0.0.0 Outgoing interface list: Serial0, Forward/Dense, 00:00:12/00:00:00 (184.108.40.206/32, 220.127.116.11), 00:00:12/00:02:48, flags: PT Incoming interface: Serial0, RPF nbr 18.104.22.168 Outgoing interface list: Null
The "00:00:12" part shows how long the entry has been up. What does "00:02:48" mean? This is the expiry timer, used to remove the entry if it does not receive multicast traffic for this (S,G) entry.
But in this case, the outgoing interface list is null, which means that none of our downstream neighbors or any hosts on our connected interfaces wants it. This router sent an (S,G) prune message to its RPF neighbor (22.214.171.124), so obviously, we won't be receiving multicast traffic for this (S,G) entry.
Given this information, what does the timer "00:02"48" mean in this context? Is it a count down timer for the router to send a state refresh or another prune message for this (S,G) entry, provided that the outgoing interface list remains null?