Use cases for this bidirectional is when your application is many to
many where you are both the sender and the receiver and want to cut down the
number of entries in the routing table
- We can use Bidir when we have lots of senders that are also receivers in the Multicast Network
- Traditional sparse mode forms two trees
o
Unidirectional SPT from source to RP
o
Unidirectional shared tree from RP to receivers
- Results in (*,G) and (S,G) entries in control plane
o
For many to many multicast application, doesn’t
scale well
- Bidirectional PIM solves by only allowing the shared tree (*,G) and never a SPT(S,G)
How Bidirectional PIM works
- Defie an RP and group rnage as bidirectional
o
Stops formation of (S,G) for that range
- Build single (*,G) tree towarfs RP
o
Traffic flows upstream from source to RP
o
Traffic flows downstream from RP to receivers
- Removes PIM Register process
o
Implies that traffic from sources always flows
to the RP
- Uses designated forwarder (DF) for loop prevention
- One DF is elected per PIM segment
o
Similar to assert, lowest metric to the RP wins
o
Highest IP address in tie
- Only DF can forward traffic upstream towards RP
- All other interfaces in OIL are downstream facing
- Removes the need for RPF check
o
Due to this all routers must agree on Bidir or
loops can occur
- Router (config) # ip multicast-routing
- Router (config)# ip pim bidir-enable
- Router (config)# ip pim rp-address x.x.x.x bdir
SHOW command
-
Router # show ip mroute· Router # show ip pm rp mapping· Router # show run | inc bidir· Router # show ip mfib count
LAB CONFIGURATION
Router 2 configuration
This lab router 2 is RP bi-direcitonal
Checking mroute for routers
After ip igmp join group 224.1.1.1
REFERENCE
- https://ine.com
- https://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/fsbidir.html
- https://www.cisco.com/c/dam/en/us/products/collateral/ios-nx-os-software/multicast-enterprise/prod_white_paper0900aecd80310db2.pdf
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