Multicast - Implementing Multicast (MCAST V1.0) - PIM Bi-Dir (6)

- idea:use the sam tree for traffic from sources toward RP an from RP to receivers
- benefits: less states in routers (many sources for the same group produce one (*,G) only
- traffic forwarded natively (hop-by-hop) toward RP rather than registered (designated forwarders)
- initally routers responsible for sending (*,G) Joins toward RP and routers responsible for forwarding group traffic toward RP have to identify the group as bidir
- DF (designated forwarder) Router on the Link with the best unicast route to RP
- DF for a particular BiDir PIM group exists on every link within a PIM domain (also p2p)
- Receiver join toward RP
* no changes, PIM SM (*,G) joins are forwarded by last-hop designated router toward RP serving the group.
- when router receives join for bidir group it must determine if it is the DF on the link, if it is DF, it follows normal (*,G) join procedure otherwise discard the join


Designated Forwarder Election

- elets the router on the link with the best paths to the RP
- ensures all routers on link have a consistent view
- unicast routing metrics used to decide between paths through different routers


- DF Election Messages
* Offer - used to advertise local metrics to reach the RP
* Winner - used by DF to announcing its status
* Backoff - used by DF upon receipt of a better Offer
* Pass - used by DF to pass DF responsiblity to better candidate


-DF dies : downstream router will notice a change in the RPF provided by unicast routing
-DF advantages
* enforces a single forwarder for traffic in both directions between a link and the rp
* responsible for originating joins for local receivers
* eliminating loops that were previously possible because of DR placement


Configuring PIM-bidir (BSR)

Router1(config)#ip pim bidir-enable
Router1(config)#ip access-list standard ACL123
Router1(config-std-nacl)#permit host 239.0.0.1
Router1(config)#ip pim rp-candidate Loopback0 group-list ACL123 bidir 
!239.0.0.1 as PIM-SM-Bidir, deny ip any any -> PIM DM
Router1(config)#ip pim bsr-candidate Loopback0 4

Note:By default a bidirectional RP advertises all groups as bidirectiona


Configuring PIM-bidir (AutoRP)

Router1(config)#ip pim bidir-enable
Router1(config)#ip access-list standard ACL123
Router1(config-std-nacl)#permit host 239.0.0.1
Router1(config)#ip pim send-rp-announce Loopback0 scope 10 group-list ACL123 bidir
!239.0.0.1 as PIM-SM-Bidir, deny ip any any -> PIM DM

Look if AutoRP is running

Router1#sh ip pim autorp 
AutoRP Information: 
  AutoRP is enabled.
Router1#

Also see Cisco IOS Multicast Configuration Guide