111 © 2003, Cisco Systems, Inc. All rights reserved. Presentation_ID

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Session NumberPresentation_ID

Bidirectional PIM

Thom Bryant

June 2003

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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

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Bidirectional PIM–Sources

Source

RP

• Traffic forwarded natively toward RP rather than registered

• RP identified for bidir groups (static or auto-RP)

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1

2

Source

RP

DF

Designated Forwarder elected per subnet based on metric to RP

Bidirectional PIM–Designated Forwarder

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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

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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

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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

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Questions?

Thank you

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