02_5_1_组播PIM-SM-bidir

2019年7月27日 01:59 作者：金淼淋分类：Multicast  609

YES LAB
Bidirectional PIM and Source Specific
Multicast

Objectives
YES LAB
Upon completion of this section, you will be
able to perform the following tasks:
— Explain the operation of PIM SM bidirectional
mode and configure it
— Describe the principles of Source-Specific
Multicast

Bidirectional PIM
YES LAB
— Idea: Use the same tree for traffic from sources toward 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

Bidirectional PIM—Source
YES LAB
• RP identified for bidir groups (statically/dynamically)
Source 2
Source I
Receiver
Receiver

Bidirectional PIM—Source
YES LAB
• RP identified for bidir groups (statically/dynamically)
• Traffic forwarded natively (hop-by-hop) toward RP rather than
registered (using designated forwarders)
Source 2
Source I
Receiver
Receiver

Bidirectional PIM
• Receivers join toward RP
— Receive
YES LAB
Receiver
Source 2
(v, G) Join
Forwarding state
Source I
Receiver

Bidirectional PIM
• Receivers join toward RP
— Receive
YES LAB
• Forwarding state created with RPF toward RP as the IIF
Source 2
(v, G) Join
Forwarding state
Source I
Receiver
Receiver

Bidirectional PIM—Traffic Fl
YES LAB
• Branches of bidirectional distribution tree established
Source 2
DF
Source 1
Receiver
Receiver

Bidirectional PIM—Traffic Fl
YES LAB
• Branches of bidirectional distribution tree established
• Traffic flows natively toward RP (forwarded by DF) and can be
forwarded directly on a branch toward interested receivers
without first reaching RP
Source 2
DF
Source 1
Receiver
Receiver

PIM Modifications for Bidirectional
Operation
YES LAB
— On each link the router with the best path to the
RP is elected to be the designated
forwarder (DF)
— The DF is responsible for forwarding upstream
towards the RP
— No special treatment is required for local sources

Forwarding/ Tree Building
• The DF forwards all traffic
from the link upstream
toward the RP
YES LAB

Forwarding/ Tree Building
• The DF forwards all traffic
from the link upstream
toward the RP
• Downstream routers with
receivers Join towards the DF
i Join to DF
RI

Forwarding/ Tree Building
• The DF forwards all traffic
from the link upstream
toward the RP
• Downstream routers with
receivers Join towards the DF
• DF adds link to ( * , G) oilist
and Joins towards the RP
Join
i Join to DF
RI

$Designated Forwarder Electi YES LAB — Elects the router on the link with the best path to the RP n/J\B3MetricsfÄ , , — Ensures all routers on link have a consistent view of the winner identity and metrics — Unicast routing metrics and assert comparison rules are used to decide between paths through different routers$

DF Election Messages
YES LAB
— Offer—Used to advertise local metrics to reach
the RP
— Winner—Used by a DF announcing or reasserting
its status
— Backoff—Used by a DF upon receipt of a better
Offer
— Pass—Used by an acting DF to pass the DF
responsibility to a better candidate

Initial Election (cont.)
• On RP discovery send offer
with RP metric
• Neighbors compare with own
metric and back off unless
better
• After repeating 3
uncontested Offers, send a
Become DF
I Winner 8
Winner and assume DF role
DFis NI
YES LAB
DF is NI

DF Advantages
YES LAB
— DF election enforces a single forwarder for traffic
in both directions between a link and
the
— DF is responsible for originating Joins for local
receivers thus eliminating loops that were
previously possible because of DR placement.

Configuring PIM bidir
(Example with BSR)
YES LAB
int-ecLuce
i p pi m enable
(9, 22.1. 1.1), L lug, .
1 u. 1.1.
i nt.evfar.e. 7 i.' t. :
F X'LELh(-znuLO/0, 00:
Out. going I i u L :
se, 00 : 1 1

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