multicast routing babu ram dawadi

Multicast RoutingMulticast Routing

Babu Ram DawadiBabu Ram Dawadi

IndexIndexa) What is a multicast routing protocol?

b) What are the differences between dense mode and sparse mode protocols?

c) What is PIM-SM?

d) What is RPF (Reverse Path Forwarding)?

e) What is MRIB?

f) Explain the three phases of PIM-SM. GWE.

g) Explain the roles of Designated Routers.

h) Explain the roles of Rendezvous Points.

i) Explain how a RPT to SPT switch is triggered.

j) Learn how to see the above processes using XORP. GWE.

What is a multicast routing protocol?What is a multicast routing protocol?

Multicast Routing ProtocolMulticast Routing Protocol Multicast communications is define as one-to-many or many-to-many Multicast communications is define as one-to-many or many-to-many

communicationscommunications

In multicasting, the router may forward the received packets through In multicasting, the router may forward the received packets through several of its interfaces.several of its interfaces.

In this case, router may copy the data when it is necessary, and forward it In this case, router may copy the data when it is necessary, and forward it to the receivers.to the receivers.

Fig. 1. Multicast RoutingFig. 1. Multicast Routing

`

Source (S)

`

Receiver 3

`

Receiver 2

`

Receiver 1

The router may forward The router may forward received packets through received packets through

several interfacesseveral interfaces

Multicast Routing Protocol Multicast Routing Protocol (cont)(cont)

Multicast routing protocol doesn’t support reliable transport layer protocol Multicast routing protocol doesn’t support reliable transport layer protocol such as TCPsuch as TCP– Source does not care about how many downstream receivers are receiving the

data– It is impossible to maintain the reliable TCP connections with all of the

receivers.User Layer

Socket Layer

Stream Sockets Datagram Sockets Multicast Sockets

TCP UDP

IP IP Multicast

Network Interface

Fig. 2. Multicast Routing Protocol StackFig. 2. Multicast Routing Protocol Stack

UDP is commonly used for UDP is commonly used for multicast traffic.multicast traffic.

If a packet is missed by receiver, If a packet is missed by receiver, the packet will simply lost and will the packet will simply lost and will

not be retransmitted not be retransmitted

Multicast Routing ProtocolMulticast Routing Protocol Multicast Routing Protocol consists of:Multicast Routing Protocol consists of:

– DVMRP (Distance Vector Multicast Routing Protocol)– PIM-DM (Protocol Independent Multicast - Dense Mode)– CBT (Core Based Tree)– PIM-SM (Protocol Independent Multicast – Sparse Mode)– and others…….

They each serve a different purpose.They each serve a different purpose.

RoutingRouting

Dense ModeDense Mode

DVMRPDVMRP PIM-DMPIM-DM

Fig. 2. Types of Unicast Routing ProtocolFig. 2. Types of Unicast Routing Protocol

Sparse ModeSparse Mode

PIM-SMPIM-SM CBTCBTPIMPIM

Dense Mode Multicast Routing ProtocolDense Mode Multicast Routing Protocol

DVMRP and PIM-DM are the 2 examples of multicast routing DVMRP and PIM-DM are the 2 examples of multicast routing protocol in this category.protocol in this category.

As the name implies, Dense Mode is optimized for densely As the name implies, Dense Mode is optimized for densely populated communities of receivers.populated communities of receivers.

Using Source based tree (S,G)Using Source based tree (S,G)

Routers simply floods multicast traffic streams to all interfaces. Routers simply floods multicast traffic streams to all interfaces. (FLOOD)(FLOOD)

If downstream routers have no receiver require this particular If downstream routers have no receiver require this particular multicast stream, it will send “stop” message to upstream router. multicast stream, it will send “stop” message to upstream router. (PRUNE)(PRUNE)

Dense Mode – Flood and PruneDense Mode – Flood and Prune

Source

Receiver

Multicast Packets

Routers simply floods Routers simply floods multicast traffic streams multicast traffic streams to all interfacesto all interfaces (S, G) State created in

everyevery router in the network!


Source

Receiver

Multicast Packets

Prune Messages

Downstream routers have Downstream routers have no receiver, so send a no receiver, so send a prune messages to prune prune messages to prune unwanted traffic.unwanted traffic.


Source

Receiver

Multicast Packets

Finally, after pruning, only Finally, after pruning, only downstream with receiver will downstream with receiver will receive the traffic. But the Flood receive the traffic. But the Flood and prune process will repeat and prune process will repeat every 3 minutesevery 3 minutes

Sparse Mode Multicast Routing ProtocolSparse Mode Multicast Routing Protocol

PIM-SM or CBTPIM-SM or CBT

Routers must specifically request a particular multicast stream before the Routers must specifically request a particular multicast stream before the data is forwarded to them.data is forwarded to them.

PIM SM implements forwarding trees for each multicast groupPIM SM implements forwarding trees for each multicast group– creating routing tree for a group with Rendezvous Point (RP) as a root for

the tree– Rendezvous Point Tree (RPT)

Explicit join modelExplicit join model– Receivers send Join towards the RP– Sender send Register towards the RP

Support both Source Based Tree (S,G) and Shared Based Tree (*,G)Support both Source Based Tree (S,G) and Shared Based Tree (*,G)

Reverse Path Forwarding (RPF)Reverse Path Forwarding (RPF) RPF is used to verify that a router receives a multicast packet on RPF is used to verify that a router receives a multicast packet on

the correct incoming interface.the correct incoming interface.

RPF algorithm RPF algorithm – makes use of the existing unicast routing table to determine the upstream

and downstream neighbors

Using unicast routing information Using unicast routing information – to create a distribution tree along the reverse path from the receivers

towards the source

RPF check helps to guarantee that the distribution tree will be RPF check helps to guarantee that the distribution tree will be loop-freeloop-free

Reverse Path Forwarding (RPF)Reverse Path Forwarding (RPF)

Multicast Route TableMulticast Route TableNetwork Network InterfaceInterfaceFF02::/16FF02::/16 eth0eth0

`

`

SourceSourceFF02::101/16FF02::101/16

Receiver 1Receiver 1

Receiver 2Receiver 2

Router 1Router 1

Router 2Router 2

Router 3Router 3

eth0eth0

eth1eth1

eth2eth2

eth0eth0

eth1eth1

eth2eth2

eth0eth0

eth1eth1

eth2eth2

MRIB - MRIB - Multicast Routing Information Base Multicast Routing Information Base

Multicast Routing Information Base Multicast Routing Information Base

Multicast topology table Multicast topology table

Derived from the unicast routing table or from other routing Derived from the unicast routing table or from other routing protocolsprotocols– Unicast routing table

• OSPF

PIM-DM uses the MRIB to make decisions regarding RPF PIM-DM uses the MRIB to make decisions regarding RPF interfaces.interfaces.– PIM know where to send (*,G) and (S,G) Join/Prune messages

Three phases of PIM-SMThree phases of PIM-SM 3 phases of PIM – SM to build a multicast distribution tree3 phases of PIM – SM to build a multicast distribution tree

– RP Tree

– Register Stop

– Shortest Path Tree

Rendezvous Points Tree (RPT)Rendezvous Points Tree (RPT) In shared treeIn shared tree

– Root of the distribution tree is a router, not a host

In PIM-SM multicast routing protocolIn PIM-SM multicast routing protocol– the core router at the root of the shared tree is the rendezvous point (RP )– The traffic from upstream and join/prune message from downstream

routers “rendezvous” at this core router.

To join the Shared Tree (host want to receive multicast traffic)To join the Shared Tree (host want to receive multicast traffic)– Router or DR executes an RPF check on the RP address in its routing table– Produces the interface closest to the RP. – Send a join message (*,G) out on this interface.

These upstream routersThese upstream routers– Repeat the those 3 processes until it reaches the RP.– It is building the shared tree or RPT as it goes until it reaches the RP.

Register StopRegister Stop Sources of multicast traffic don't necessarily join the group to Sources of multicast traffic don't necessarily join the group to

which they are sending datawhich they are sending data– First Hop Router (FHR) or DR can receive the traffic without knowing the

information on how to send the traffic to the RP through the tree.– It encapsulates the packet and send to RP as unicast packet.(Register

Msg)– RP de-encapsulates theRegister message and forwards the extracted data

packet to downstream members on the RPT

Encapsulation at DR and decapsulation for Register message at Encapsulation at DR and decapsulation for Register message at RP is not efficientRP is not efficient– RP initiates a (S,G) Join toward S and the path to source is established.– DR starts sending traffic from S using both native multicast and Register-

encapsulated messages– RP detected a duplicated multicast packets, it will send a “Register Stop”

message to tell DR stop sending Register Message.– DR stop sending the Register message and RP now only receive the packet

from native multicast packet.

Shortest Path Tree (SPT)Shortest Path Tree (SPT) RP is a place for a source and receivers to meetRP is a place for a source and receivers to meet

– But if there is too many multicast group “rendezvous” there, it might become a bottleneck

Hence, establishing SPT might solve this problem and also reduce Hence, establishing SPT might solve this problem and also reduce the path delay from Source to receivesthe path delay from Source to receives– SPT can be accomplish by specifying an SPT-Threshold in terms of

bandwidth.– If this threshold is exceeded, the last-hop DR joins the SPT

To build the SPT To build the SPT – Router executes an RPF check on the source address in its routing table to

find the interface closest to the source.– Issues an (S,G) Join to the RPF next router toward S.

Shortest Path Tree (SPT) Shortest Path Tree (SPT) (cont)(cont)

Each upstream router repeats this process, untilEach upstream router repeats this process, until– Arrives at the subnet of S – Router that already has (S,G) Join state.

The DR at the Source subnet then starts forwarding packets onto The DR at the Source subnet then starts forwarding packets onto the source tree to the receiverthe source tree to the receiver

Now, the receiver's DR, it receives packets from Shared Tree (RP) Now, the receiver's DR, it receives packets from Shared Tree (RP) and Source Tree (SPT). To stop receiving duplicating traffics,and Source Tree (SPT). To stop receiving duplicating traffics,– Receiver's DR sends a PIM Prune message towards the RP router.– This message is known as (S,G,rpt) Prune, to tell RP this particular traffic This message is known as (S,G,rpt) Prune, to tell RP this particular traffic

coming in from the RPT are no longer neededcoming in from the RPT are no longer needed

PIM Prune message is received by the RP router, then it stops PIM Prune message is received by the RP router, then it stops sending this particular multicast traffic down to the receiver's DR.sending this particular multicast traffic down to the receiver's DR.

Designated Routers (DR)Designated Routers (DR) The DR is a router which directly-connected to receivers and The DR is a router which directly-connected to receivers and

sources.sources.

Sets up multicast route entriesSets up multicast route entries

Sends corresponding Join/Prune and Register messages on Sends corresponding Join/Prune and Register messages on behalf of receivers and sources.behalf of receivers and sources.

The sender with the largest IP The sender with the largest IP address assumes the role of DR address assumes the role of DR

Receiver 1`

10.207.160.0/24

10.207.160.100

10.207.160.1 10.207.160.2

RPRP

Router A Router B

If multiple routers If multiple routers exist on a single exist on a single segment, segment, “designated router” “designated router” will be electedwill be elected

DRDR

Roles of Rendezvous PointsRoles of Rendezvous Points The RP is the root of particular group shared treeThe RP is the root of particular group shared tree

– RP-Tree.

The distribution center of PIM-SMThe distribution center of PIM-SM– Multicast the traffic from the source to the downstream routers that have

receivers– Responsible for forwarding information from the source to all registered Responsible for forwarding information from the source to all registered

receivers.receivers.

Source

Receiver 1

RP

`

R1

PIM-SM – Joining the Shared TreePIM-SM – Joining the Shared Tree

Receiver 1 Joins Group G, and Router (R1) creates (*,G) state and send the (*, G) Join message to its upstream PIM neighbor, in the direction to the RP

(*,G) was created only along the shared tree

RP created the (*,G) state

IGMP or MLD, Receiver listen to Group, G

Last Hop Router(LHR)

First Hop Router(FHR)

PIM-SM – Registering with the RPPIM-SM – Registering with the RP

Source

Receiver 1

RP

`

R1Legend

Shared tree

Sources of multicast traffic can always send the traffic. They no need to Join to any group


FHR will send a “register” message to the RP. Theregister message is a unicast message addressed directly to the RP

The multicast data from the source (including headers) is encapsulated in the register message so that the RPcan forward the data while adding the source to the tree

Multicast Traffic Flow(S,G) Register message - - - - unicast

RP de-encapsulates each Register message and forwards the extracted data packet to downstream members on the RPT RP add FHR into the RPTRP sends PIM “join” to FHR.

(S,G) Join MessageSource Tree

Once the shortest path is established, from the source to the RP, the FHR begins sending traffic to the RP as standard IP multicast packets as well as encapsulated within Register messages.RP will temporary receive some packets twice.

RP detects the normal multicast packets, it sends a Register-Stop message to FHR, ask FHR to stop sending register packets.

Multicast Traffic Flow


PIM-SM – Registering with the RPPIM-SM – Registering with the RP

Source

Receiver 1

RP

`

R1

Shared tree

Legend

Source Tree

Source traffic flows nativelyalong SPT to RP.

The multicast traffic flown down from RP to Receiver through Shared Tree

Multicast Traffic Flow



Source

Receiver 1

RP

`

R1

The LHR now receives two copies of the multicast traffic packets - source node- Rendezvous Point (RP).

PIM-SM – Shortest Path Tree PIM-SM – Shortest Path Tree (switching)(switching)

Shared tree

Legend

Source TreeMulticast Traffic Flow



Additional (S, G) State is created along new part of the Source Tree

Traffic begins flowing down the new branch of the Source Tree

Additional (S, G) State is created along the Shared Tree to prune off (S, G) traffic.

(S, G) Prune Message

(S, G) Traffic flow is now pruned off of the Shared Tree and is flowing to the Receiver via the Source Tree.

(S, G) traffic flow is no longer needed by the RP so it Prunes the flow of (S, G) traffic.

When a downstream router detects there is an available shorter path, it can send a PIM-SM “join” message directly to the FHR.

(S, G) Traffic flow is now only flowing to the Receiver via a single branch of the Source Tree and Receiver is receiving traffic using SPT

Summary: Dense mode vs Sparse mode diagramSummary: Dense mode vs Sparse mode diagram

Sparse ModeSparse Mode Dense ModeDense Mode

XORP ConfigurationXORP Configuration

XORP IntroductionXORP Introduction Extensible Open Router Platform Extensible Open Router Platform

Multicast routing protocols for IPv4 and IPv6 Multicast routing protocols for IPv4 and IPv6

XORP is free XORP is free

The XORP core developer teamThe XORP core developer team– International Computer Science Institute in Berkeley, California

XORP-InstallationXORP-Installation XORP can be divided into two subsystems:XORP can be divided into two subsystems:

– kernel-spacekernel-space– user-spaceuser-space

kernel-spacekernel-space– handles the forwarding path and provides API to the userspacehandles the forwarding path and provides API to the userspace– MROUTING kernel option must be activatedMROUTING kernel option must be activated– PIM kernel option must be activated in order to run PIM-SMPIM kernel option must be activated in order to run PIM-SM

User-spaceUser-space– Default Configuration file: /usr/local/xorp/config.bootDefault Configuration file: /usr/local/xorp/config.boot– Requirements : GNU make and Net-SNMPRequirements : GNU make and Net-SNMP

XORP-ConfigurationXORP-Configuration

interfaces {interfaces { interface rl0 {interface rl0 { description: "upstream interface"description: "upstream interface" disable: falsedisable: false default-system-configdefault-system-config }}

interface rl1 {interface rl1 { description: "downstream interface"description: "downstream interface" disable: falsedisable: false default-system-configdefault-system-config }}}}

Explicitly enables the two rl0 and rl1 physical interfaces for XORP operation.

default-system-config-Tell FEA that the interface is configured using the existing interface information from the underlying system.

XORP-Configuration XORP-Configuration (cont)(cont)

plumbing {plumbing { mfea6 {mfea6 { disable: falsedisable: false interface rl0 {interface rl0 { vif rl0 {vif rl0 { disable:falsedisable:false }} }} interface rl1 {interface rl1 { vif rl1 {vif rl1 { disable falsedisable false }} }} interface register_vif {interface register_vif { vif register_vif {vif register_vif { disable: falsedisable: false }} }} }}}}

mfea6 (Multicast Forwarding Engine Abstraction)-must be configured if the XORP router is to be used for IPv6 multicast routing.

vif( virtual interface)-To enable or disable vif to be used for multicast IPv6 forwarding. In this example, we are not using it.

interface register_vif-Enable it for PIM-SM operation, it is for PIM-SM register messages and must enable in mfea is PIM-SM is configured.


protocols {protocols { mld {mld { disable: falsedisable: false interface rl0 {interface rl0 { vif rl0 {vif rl0 { disable: falsedisable: false }} }}

interface rl1 {interface rl1 { vif rl1 {vif rl1 { disable: falsedisable: false }} }}

}}

MLD(Multicast Listener Discovery)-MLD is configured if the XORP router is to be used for multicast routing

- Track multicast group membership for directly connected subnets.


pimsm6 {pimsm6 { disable: falsedisable: false interface rl0 {interface rl0 { vif rl0 {vif rl0 { disable: falsedisable: false }} }}

interface rl1 {interface rl1 { vif rl1 {vif rl1 { disable: falsedisable: false }} }}

interface register_vif {interface register_vif { vif register_vif {vif register_vif { disable: falsedisable: false }} }}

pimsm6-If the XORP router is used for multicast routing for the PIM-SM domain, the PIM-SM should be configured.

dr-priority - This command is used for setting the priority for the XORP router. If this command is not stated in the configuration, default priority value =1 will be used.

-This parameter is used for the Designated Router election.


bootstrap {bootstrap { disable: falsedisable: false cand-bsr {cand-bsr { scope-zone ff00::/32 {scope-zone ff00::/32 { cand-bsr-by-vif-name: "rl1"cand-bsr-by-vif-name: "rl1" bsr-priority: 128bsr-priority: 128 hash-mask-len: 30hash-mask-len: 30 }} }}

cand-rp {cand-rp { group-prefix ff00::/32 {group-prefix ff00::/32 { cand-rp-by-vif-name: "rl1"cand-rp-by-vif-name: "rl1" rp-priority: 192rp-priority: 192 rp-holdtime: 150rp-holdtime: 150 }} }}}}

bootstrap-Mechanism for elect RP dynamically.

cand-bsr-Configured the XORP routers as candidate Bootstrap Routers (BSR)

Scope-zone-A router intended to be a Candidate-BSR it must advertise for each zone (scope-zone & non-scope-zone)

bsr--priority-Router with the highest priority value will be elected as BSR.

Hash-mask-len-Unknown, leave it as default

cand-rp-XORP router is to be a Candidate-RP,

group-prefix- Candidate-RP it must advertise for each zone

rp-priority- Router with highest priority will be elected as RP


switch-to-spt-threshold {switch-to-spt-threshold { /*approximately 1K bytes/s (10Kbps) threshold *//*approximately 1K bytes/s (10Kbps) threshold */ disable: falsedisable: false interval: 100interval: 100 bytes: 102400bytes: 102400 }} }}

Switch-to0spt-threshold-used to specify the multicast data bandwidth threshold.-Used for Shortest Path Tree (SPT) switching

interval: 100bytes: 102400-if total 10240 bytes arrive within 100 seconds, switch to SPT


fib2mrib {fib2mrib { disable: falsedisable: false }}}}

fib2mrib-If the unicast routing protocol is not configured in and inject routes into MRIB, this parameter will be used.

- It will get the Forwarding Information Base (FIB) from the system and pass it to the MRIB.

XORP XORP –– Case Study (Practical) Case Study (Practical)

XORP – Case Study (Topology)XORP – Case Study (Topology)

2001:d30:1EF:1::/64

2001:d30:1EF:3::/64

2001:d30:1EF:5::/642001:d30:1EF:4::/64

2001:d30:101:EF::/64

em1 ::1:1

em0 ::1:3em0 ::1:2

em1 ::2:2

em0 ::2:5

em1 ::5:5

em0 ::3:6

em1 ::4:6

Router-51

Router-53

Router-56

Router-52

Router-55

`

rtadvd

` rtadvd

Receiver

Source

RPRP

Initial State – No QueriesInitial State – No QueriesRouter-51

Router 51 knows where is the RP located, it is at Router 2001:d30:1ef:5::5:5 Router 51 knows where is the RP located, it is at Router 2001:d30:1ef:5::5:5 Router 51 knows where is the BSR located, it is at Router 2001:d30:1ef:5::5:5 Router 51 knows where is the BSR located, it is at Router 2001:d30:1ef:5::5:5

To show interfaces status

To show Bootstrap and RP info

To show RP info only

To show bootstrap info only

AA BB

CC DD

Initial State – No Queries Initial State – No Queries (cont)(cont)

Router-52






AA BB

CC DD


Router-53






AA BB

CC DD


Router-55RP

BSR

Router 55 is configured as a BSR and RP statically, in the diagram B and C , there is anRouter 55 is configured as a BSR and RP statically, in the diagram B and C , there is an additional information about BSR and RP in Router 55. additional information about BSR and RP in Router 55.





AA BB

CC DD


Router-56






AA BB

CC DD


Router-51

Router-55

Router-54

Router-53

Router-52

All show pim6 join return an empty result because

there is no request from the receiver

Initial State – No QueriesInitial State – No Queries

Router-51

Router-53

Router-56

Router-52

Router-55

`

`

Receiver

Source

RPRP

BSRBSRDR

NOT DR

NOT DR

NOT DR

em1

VIF

em1

em0

em0em0

em0 em0

em1em1

em1

DR

NOT DR

DR

DR

DR

NOT DR

Summary for the DR

election on this topology

Case Study : XORP Configuration & Case Study : XORP Configuration & ObservationObservation

Phase 1 Building RP TreePhase 1 Building RP TreePhase 2 Register Start/StopPhase 2 Register Start/Stop

Receiver wishes to receive - RequestReceiver wishes to receive - Request

2001:d30:1EF:1::/64

2001:d30:1EF:3::/64

2001:d30:1EF:5::/642001:d30:1EF:4::/64

2001:d30:101:EF::/64

em1 ::1:1

em0 ::1:3em0 ::1:2

em1 ::2:2

em0 ::2:5

em1 ::5:5

em0 ::3:6

em1 ::4:6

Router-51

Router-53

Router-56

Router-52

Router-55

`

`

Receiver

Source

RPRPRequestRequest

(*,G)(*,G)

(*,G)(*,G)(*,G)(*,G)

(*,G)(*,G)

2001:d30:101:EF:20c:29ff:fe9f:f3af

Now, the receiver intended to receive a traffic, Thus, receiver make a request to Router-56

Receiver wishes to receive - RequestReceiver wishes to receive - Request

`

Receiver

Request

An example of the screen shot on

using SSMPINGD at receiver

Building RP TreeBuilding RP TreeRouter-51

Now there is a receiver request for the traffic. In show pim6 join, it shows that Router-51 is directly connected to the source.

In the upstream, there is no RP forwarder. But Router-51 knows where is the RP for this particular group. It sends the Register message to RP. The status now is the FHR had joined to the RP (Router-55)

Route-51 is directly connected to the source through em0, and RP is connected at direction of em1

Router-51 is connected to (S,G) through vif

Building RP Tree Building RP Tree (cont)(cont)

Router-52

WC = Wild Card (*,G)If Router 52 found that there is no more specific match for particular source , the packet will be forwarded according to the next hop entry.

Current status for Router-52 is joined to the multicast group

RP is connected towards at interface em1

DR is at em0.DR at em0 join the multicast wildcard entry for the group


Router-53




DR is at em1.DR at em1 join the multicast wildcard entry for the group


Router-55Router-55 is RP, it joins to the FHR through vif using Register Message



Router-56




DR is at em1.DR at em1 create the multicast wildcard entry for the group

Registering with the RPRegistering with the RP

PIM-SM Register MessagePIM-SM Register Message

XORP XORP –– Case Study (Practical) Case Study (Practical)

Phase 3 Shortest Path TreePhase 3 Shortest Path Tree

Shortest Path Tree (SPT)Shortest Path Tree (SPT)

em1

em0em0

em1

em0

em1

em0

em1

Router-51

Router-53

Router-56

Router-52

Router-55

`

`

Receiver

Source

RPRPRequestRequest

(*,G)(*,G)

(*,G)(*,G)(*,G)(*,G)

(*,G)(*,G)X

X X

X(S,G)(S,G)

(S,G)(S,G)

(S,G)(S,G)

The The distance distance

becomes 3 becomes 3 hopshops


`

Receiver

Receive 2 Receive 2 duplicated duplicated multicast multicast packetspackets

Router immediately Router immediately switch to SPT and switch to SPT and send a Prune send a Prune Message to RP, so Message to RP, so now receiver only now receiver only received single received single multicast packet multicast packet using SPTusing SPT


Router-52Router-52 now Router-52 now

knows sources is knows sources is at direction of at direction of

em0 and RP is at em0 and RP is at direction of em1direction of em1

Now the multicast group has Now the multicast group has switched to SPT. Since Router-52 switched to SPT. Since Router-52 is not in SPT path, a (S,G) Prune is not in SPT path, a (S,G) Prune message is sent towards RP. This message is sent towards RP. This is known as is known as (S,G,RPT) Prune(S,G,RPT) Prune and and indicating that traffic from S for G indicating that traffic from S for G should NOT be forwarded in this should NOT be forwarded in this em0em0 direction. direction.


Router-53

Now the multicast group has Now the multicast group has switched to SPT. Router-53 is now in switched to SPT. Router-53 is now in SPT path, it no longer using RPT, so SPT path, it no longer using RPT, so (S,G,RPT) Prune is sent towards RP, (S,G,RPT) Prune is sent towards RP, indicating that traffic from S for G indicating that traffic from S for G should NOT be forwarded in this should NOT be forwarded in this directiondirection

Router-53 now Router-53 now knows sources is knows sources is

at direction of at direction of em0 and RP is at em0 and RP is at direction of em1direction of em1

Router-53 receive Router-53 receive the traffic from the traffic from

the source using the source using SPTSPT


Router-55

Now the multicast group has switched Now the multicast group has switched to SPT. Since Router-55 is not in SPT to SPT. Since Router-55 is not in SPT path, and there is no other group path, and there is no other group receive traffic from the RP, the RP receive traffic from the RP, the RP send a Prune Message to the FHR send a Prune Message to the FHR (router 51) to stop receiving traffic (router 51) to stop receiving traffic from FHR. No traffic will be forwarded from FHR. No traffic will be forwarded in this in this em0em0 direction. direction.


Router-56

Router-56 receive Router-56 receive the traffic from the traffic from

the source using the source using SPTSPT

Thank youThank you

multicast routing babu ram dawadi

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