3.2b PIM dense

3.2.b Implement and troubleshoot IPv4 protocol independent multicast
3.2.b (i) PIM dense mode, sparse mode, sparse-dense mode

dense mode assumes every node in the network wants the multicast traffic, therefore dense mode floods the network. nodes not wanting the traffic must then prune. (flood and prune). uses source distribution trees (S,G)

Router(config)#ip multicast-routing
Router(config)#int f0/0
Router(config-if)#ip pim dense-mode

dense mode mechanics:

1. a source floods multicast traffic through the network

2. if more than one router is forwarding over a broadcast medium Assert messages will determine which becomes the PIM forwarder. the router with the highest metric (default: highest ip address) wins

3. Routers may not have recipients for the group currently flooded. these routers will send a prune message to their upstream router requesting their branch of the distribution tree be pruned. however if another router is on the same broadcast medium as the one who sent the prune, and if that router has attached receivers, the prune message will be treated with a join-override message.

4. if a receiver comes up on a previously pruned router, that router may rejoin the tree by sending a graft packet.

r2(config-if)#do sh ip mroute | b \(
(*,, 00:03:54/stopped, RP, flags: DC
Incoming interface: Null, RPF nbr
Outgoing interface list:
FastEthernet1/0, Forward/Dense, 00:03:54/00:00:00
FastEthernet0/0, Forward/Dense, 00:03:54/00:00:00

(,, 00:03:00/00:00:07, flags: T
Incoming interface: FastEthernet1/0, RPF nbr
Outgoing interface list:
FastEthernet0/0, Forward/Dense, 00:03:00/00:00:00

(*,, 00:06:29/00:02:01, RP, flags: DCL
Incoming interface: Null, RPF nbr
Outgoing interface list:
FastEthernet1/0, Forward/Dense, 00:05:27/00:00:00
FastEthernet0/0, Forward/Dense, 00:06:29/00:00:00

r3(config-if)#do sh ip pim neigh
PIM Neighbor Table
Mode: B – Bidir Capable, DR – Designated Router, N – Default DR Priority,
S – State Refresh Capable
Neighbor          Interface                Uptime/Expires    Ver   DR
Address                                                            Prio/Mode      FastEthernet0/0          00:09:17/00:01:20 v2    1 / DR S      FastEthernet1/0          00:09:57/00:01:39 v2    1 / S