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111© 2003, Cisco Systems, Inc. All rights reserved.Presentation_ID
2© 2003, Cisco Systems, Inc. All rights reserved.
Session NumberPresentation_ID
Bidirectional PIM
Thom Bryant
June 2003
333© 2003, Cisco Systems, Inc. All rights reserved.Presentation_ID
Bidirectional PIM
• Bidirectional shared trees appeared in Core Based Trees (CBTs) proposal first
Added to “Simple” later
• Idea: use the same tree for traffic from sources towards RP and from RP to receivers
• Benefits:
Less state in routers (many sources for the same group produce one (*,G) only)
Traffic from sources / to receivers follows the same path if on the same branch of the RP
444© 2003, Cisco Systems, Inc. All rights reserved.Presentation_ID
Bidirectional PIM–Sources
Source
RP
• Traffic forwarded natively toward RP rather than registered
• RP identified for bidir groups (static or auto-RP)
555© 2003, Cisco Systems, Inc. All rights reserved.Presentation_ID
1
2
Source
RP
DF
Designated Forwarder elected per subnet based on metric to RP
Bidirectional PIM–Designated Forwarder
666© 2003, Cisco Systems, Inc. All rights reserved.Presentation_ID
Bidirectional PIM–Receivers
Source
RP
DF
Receiver
Receiver
(*, G) Join
Forwarding state
Receivers join toward RPForwarding state created with RPF toward RP as the iif
777© 2003, Cisco Systems, Inc. All rights reserved.Presentation_ID
Source
RP
DF
Receiver
Receiver
Traffic flows natively toward RP and can be forwarded directly on a branch toward interested receivers without first reaching RP.
Traffic forwarded by Designated Forwarder toward RP
Traffic for all sources in group G, forwarded based on same *,G entry
Source
Bidirectional PIM–Traffic Flow
888© 2003, Cisco Systems, Inc. All rights reserved.Presentation_ID
PIM Bidir Modifications
• On each link, the router with the best path to the RP is elected to be the Designated Forwarder
• The Designated Forwarder is responsible for forwarding upstream towards the RP
• No special treatment is required for local sources
999© 2003, Cisco Systems, Inc. All rights reserved.Presentation_ID
Questions?
Thank you
101010© 2003, Cisco Systems, Inc. All rights reserved.Presentation_ID