- Used for many-to-may applications; videoconferencing, 'hoot-n-holler' type application; 7x24 direct party line type connection.
- Because Bidir PIM uses only shared trees for traffic distribution, this protocol needs a mechanism to get traffic from the sources to the rendezvous point. The designated forwarder provides that mechanism
- All the PIM neighbors in a subnet advertise their unicast route to the rendezvous point and the router with the best route is elected as DF. This effectively builds a shortest path between every subnet and the rendezvous point without consuming any multicast routing state (no (S,G) entries are generated).
- Use the interface command ip pim bidir-neighbor-filter to disable the PIM neighbors not able/capable/wanting to be in bidir mode
- If a router detects through “PIM Hello” messages that one of its PIM neighbors is not Bidir capable, the designated forwarder election process is aborted and no Bidir traffic would be forwarded tos/from that interface.
- remember to use the keyword overrirde to allow static pim rp-address to supersede the auto-rp announcements. ip pim rp-address <ip-address> <bidir-groups-acl> bidir override
- Troubleshooting bidir can be done with netflow v9, no mroute S,G exists to help.
Using loopback interfaces with different subnet masks for bidir redundancy, relying on 'longest' prefix match of unicast routing; I think this is slick, note the ip pim rp-address
Note the other of operation both in CLI and 'rate-limit' key word.
R5(config)#ip pim rp-address 150.1.5.5 55 bidir ?
<cr>
R5(config)#ip pim rp-address 150.1.5.5 55 override ?
bidir Group range treated in bidirectional shared-tree mode
<cr>
R5(config)#ip pim rp-address 150.1.5.5 55 override bidir
