© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 1
BSCI Module 7 Lesson 3
IP Multicasting: Multicast Routing Protocols
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 2
Objectives
Describe a multicast network in terms of the IP multicast routing protocols and processes used over various segments.
Describe multicast distribution trees including source trees and shared trees.
Describe the (S,G) and (*,G) multicast distribution trees entry formats.
Explain IP multicast routing.
Identify the characteristics of each of the PIM modes.
Describe the operation of PIM-DM, PIM-SM, and PIM sparse-dense modes.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 3
Multicast Distribution Trees
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 4
Multicast Protocol Basics
Types of multicast distribution trees:
Source distribution trees; also called shortest path trees (SPTs)
Shared distribution trees; rooted at a meeting point in the network
A core router serves as a rendezvous point (RP)
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 5
Shortest Path or Source Distribution Tree
Receiver 1
B
E
A D F
Source 1Notation: (S, G) S = Source G = Group
C
Receiver 2
Source 2
Multicast Distribution Trees
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 6
Receiver 1
B
E
A D F
Source 1Notation: (S, G) S = Source G = Group
C
Receiver 2
Source 2
Multicast Distribution TreesShortest Path or Source Distribution Tree
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 7
Multicast Distribution Trees
Receiver 1
B
E
A D F
Notation: (*, G) * = All Sources G = Group
C
Receiver 2
(RP) PIM Rendezvous Point
Shared Tree
(RP)
Shared Distribution Tree
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 8
Multicast Distribution Trees
Receiver 1
B
E
A F
Source 1 Notation: (*, G) * = All Sources G = Group
C
Receiver 2
Source 2
(RP) PIM Rendezvous Point
Shared Tree
Source Tree
D (RP)
Shared Distribution Tree
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 9
Multicast Distribution Tree Identification
(S,G) entries
For this particular source sending to this particular group
Traffic is forwarded through the shortest path from the source
(*,G) entries
For any (*) source sending to this group
Traffic is forwarded through a meeting point for this group
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 10
Multicast Distribution Trees
CharacteristicsCharacteristics of Distribution Trees
Source or Shortest Path trees
Uses more memory but optimal paths from source to all receivers; minimizes delay
Shared trees
Uses less memory but sub-optimal paths from source to all receivers; may introduce extra delay
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 11
Self Check
1. What is an advantage of Shortest Path Trees compared to Shared Trees?
2. What does multicast use to make it’s forwarding decisions?
3. In the STP notation (S,G), what do each of the characters represent?
4. What is the root of the shared tree called?
5. Compare Shared Distribution trees and SPT trees in terms of router memory and packet delivery delay.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 12
Multicast Routing
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 13
Protocols for IP Multicast Routing
PIM is used between routers so that they can track which multicast packets to forward to each other and to their directly connected LANs.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 14
Protocol-Independent Multicast (PIM) PIM maintains the current IP multicast service mode of
receiver-initiated membership.
PIM is not dependent on a specific unicast routing protocol.
With PIM, routers maintain forwarding tables to forward multicast datagrams.
PIM can operate in dense mode or sparse mode.Dense mode protocols flood multicast traffic to all parts of the network and prune the flows where there are no receivers using a periodic flood-and-prune mechanism.
Sparse mode protocols use an explicit join mechanism where distribution trees are built on demand by explicit tree join messages sent by routers that have directly connected receivers.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 15
Multicast Tree Creation
PIM Join/Prune Control Messages
Used to create/remove Distribution Trees
Shortest Path trees
PIM control messages are sent toward the Source
Shared trees
PIM control messages are sent toward RP
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 16
Multicast Forwarding
Multicast routing operation is the opposite of unicast routing.
Unicast routing is concerned with where the packet is going.
Multicast routing is concerned with where the packet comes from.
Multicast routing uses Reverse Path Forwarding (RPF) to prevent forwarding loops.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 17
Reverse Path Forwarding (RPF)
The RPF Calculation
The multicast source address is checked against the unicast routing table.
This determines the interface and upstream router in the direction of the source to which PIM Joins are sent.
This interface becomes the “Incoming” or RPF interface.
A router forwards a multicast datagram only if received on the RPF interface.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 18
Reverse Path Forwarding (RPF)
RPF Calculation
Based on Source Address.
Best path to source found in Unicast Route Table.
Determines where to send Joins.
Joins continue towards Source to build multicast tree.
Multicast data flows down tree.
10.1.1.1
E1
E2
Unicast Route TableNetwork Interface10.1.0.0/24 E0
Join
Join
E0
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 19
Reverse Path Forwarding (RPF)
10.1.1.1
E1E0
E2
Join
Join
RPF Calculation (cont.)
Repeat for other receivers…
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 20
Reverse Path Forwarding (RPF)
RPF Calculation
What if we have equal-cost paths?We can’t use both.
Tie-BreakerUse highest Next-Hop IP address.
10.1.1.1
E1E0
E2 Unicast Route TableNetwork Intfc Nxt-Hop10.1.0.0/24 E0 1.1.1.110.1.0.0/24 E1 1.1.2.1
1.1.2.11.1.1.1Join
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 21
Multicast Distribution Tree Creation
Shared Tree Example
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 22
Self Check
1. Why is Protocol Independent Multicast called Independent?
2. Describe dense mode operation.
3. What does multicast routing use to prevent forwarding loops?
4. What is the RPF interface?
5. What if the RFP calculation finds 2 equal-cost paths?
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 23
PIM Dense Mode Operation
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 24
PIM-DM Flood and Prune
Initial Flooding
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 25
PIM-DM Flood and Prune (Cont.)
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 26
PIM-DM Flood and Prune (Cont.)
Results After Pruning
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 27
Self Check
1. What happens to packets arriving through the non-RPF interface?
2. When would prune messages be sent on the RPF interface?
3. How often do prune messages expire in PIM-DM?
4. What happens when the prune messages expire?
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 28
PIM Sparse Mode Operation
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 29
PIM Sparse Mode
PIM-SM works with any of the underlying unicast routing protocols.
PIM-SM supports both source and shared trees.
PIM-SM is based on an explicit pull model.
PIM-SM uses an RP.Senders and receivers “meet each other.”
Senders are registered with RP by their first-hop router.
Receivers are joined to the shared tree (rooted at the RP) by their local DR.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 30
PIM-SM Shared Tree Join
Receiver
RP
(*, G) Join
Shared Tree
(*, G) State created onlyalong the Shared Tree.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 31
PIM-SM Sender Registration
Receiver
RP
(S, G) Join
Source
Shared Tree
(S, G) Register (unicast)
Source Tree
(S, G) State created onlyalong the Source Tree.Traffic Flow
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 32
PIM-SM Sender Registration
Receiver
RPSource
Shared Tree
Source Tree RP sends a Register-Stop back to the first-hop router to stop the Register process.
(S, G) Register-Stop (unicast)
Traffic Flow
(S, G) Register (unicast)
(S, G) traffic begins arriving at the RP through the Source tree.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 33
PIM-SM Sender Registration
Receiver
RPSource
Shared Tree
Source Tree
Traffic FlowSource traffic flows nativelyalong SPT to RP.
From RP, traffic flows downthe Shared Tree to Receivers.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 34
PIM-SM SPT Switchover
Receiver
RP
(S, G) Join
Source
Source Tree
Shared Tree
Last-hop router joins the Source Tree.
Additional (S, G) State is created along new part of the Source Tree.
Traffic Flow
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 35
PIM-SM SPT Switchover
Receiver
RPSource
Source Tree
Shared Tree
(S, G)RP-bit Prune
Traffic begins flowing down the new branch of the Source Tree.
Additional (S, G) State is created along along the Shared Tree to prune off (S, G) traffic.
Traffic Flow
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 36
PIM-SM SPT Switchover
Receiver
RPSource
Source Tree
Shared Tree
(S, G) Traffic flow is now pruned off of the Shared Tree and is flowing to the Receiver through the Source Tree.
Traffic Flow
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 37
PIM-SM SPT Switchover
Receiver
RPSource
Source Tree
Shared Tree
(S, G) traffic flow is no longer needed by the RP so it Prunes the flow of (S, G) traffic.
Traffic Flow
(S, G) Prune
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 38
PIM-SM SPT Switchover
Receiver
RPSource
Source Tree
Shared Tree
(S, G) Traffic flow is now only flowing to the Receiver through a single branch of the Source Tree.
Traffic Flow
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 39
“The default behavior of PIM-SM is that routers with directly connected members will join the Shortest Path Tree as soon as they detect a new multicast source.”
PIM-SM Frequently Forgotten Fact
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 40
PIM-SM Evaluation
Effective for Sparse or Dense distribution of multicast receivers
Advantages:
Traffic only sent down “joined” branches
Can switch to optimal source-trees for high traffic sources dynamically
Unicast routing protocol-independent
Basis for inter-domain multicast routing
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 41
Multiple RPs with Auto RP
PIM Sparse-Dense-Mode
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 42
Self Check
1. What types of deployments is PIM-SM appropriate for?
2. When using PIM-SM, to what device does the receiver send a Join when wishing to receive multicast traffic?
3. How is a Register message used?
4. Explain the implications of the default value of the SPT-Threshold in Cisco routers.
5. Describe the potential issues with PIM-SM.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 43
Summary IP multicast requires multiple protocols and processes for proper packet
forwarding.
Source and shared trees may be used to define multicast packet flows to group members.
Multicast routing utilizes the distribution trees for proper packet forwarding.
PIM is the routing protocol for multicast.
PIM-DM uses flood and prune.
PIM-SM uses less device and bandwidth resources and is typically chosen to implement multicast.
PIM sparse-dense mode is the recommended methodology for maximum efficiency in IP multicast.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 3 45
Resources
Internet Protocol IP Multicast Technologyhttp://www.cisco.com/en/US/tech/tk828/tech_brief09186a00800a4415.html
IP Multicast Deployment Fundamentalshttp://www.cisco.com/en/US/tech/tk828/tech_brief09186a00800e9952.html
Cisco IOS Multicast Q&Ahttp://www.cisco.com/en/US/tech/tk828/technologies_q_and_a_item09186a00801bb25d.shtml
Top Related