1. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 1 IP Multicasting: Multicast Routing Protocols

2. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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.

3. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 3 Multicast Distribution Trees

4. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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)

5. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 5 Shortest Path or Source Distribution Tree Receiver 1 B E A D F Source 1 Notation: (S, G) S = Source G = Group C Receiver 2 Source 2 Multicast Distribution Trees

6. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 6 Receiver 1 B E A D F Source 1 Notation: (S, G) S = Source G = Group C Receiver 2 Source 2 Multicast Distribution Trees Shortest Path or Source Distribution Tree

7. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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

8. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 8 Multicast Distribution Trees Receiver 1 B E AF Source 1Notation: (*, G) * = All Sources G = Group C Receiver 2 Source 2 (RP) PIM Rendezvous Point Shared Tree Source Tree D(RP) Shared Distribution Tree

9. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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

10. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 10 Multicast Distribution Trees Characteristics Characteristics 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

11. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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.

12. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 12 Multicast Routing

13. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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.

14. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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.

15. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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

16. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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.

17. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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.

18. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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 Table Network Interface 10.1.0.0/24 E0 Join E0

19. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 19 Reverse Path Forwarding (RPF) 10.1.1.1 E1E0 E2 Join RPF Calculation (cont.)  Repeat for other receivers…

20. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 20 Reverse Path Forwarding (RPF) RPF Calculation  What if we have equal-cost paths? We can’t use both.  Tie-Breaker Use highest Next-Hop IP address. 10.1.1.1 E1E0 E2 Unicast Route Table Network Intfc Nxt-Hop 10.1.0.0/24 E0 1.1.1.1 10.1.0.0/24 E1 1.1.2.1 1.1.2.11.1.1.1 Join

21. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 21 Multicast Distribution Tree Creation Shared Tree Example

22. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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?

23. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 23 PIM Dense Mode Operation

24. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 24 PIM-DM Flood and Prune Initial Flooding

25. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 25 PIM-DM Flood and Prune (Cont.)

26. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 26 PIM-DM Flood and Prune (Cont.) Results After Pruning

27. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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?

28. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 28 PIM Sparse Mode Operation

29. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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.

30. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 30 PIM-SM Shared Tree Join Receiver RP ( *, G) Join Shared Tree ( *, G) State created only along the Shared Tree.

31. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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 only along the Source Tree. Traffic Flow

32. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 32 PIM-SM Sender Registration Receiver RP Source 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.

33. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 33 PIM-SM Sender Registration Receiver RP Source Shared Tree Source Tree Traffic Flow Source traffic flows natively along SPT to RP. From RP, traffic flows down the Shared Tree to Receivers.

34. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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

35. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 35 PIM-SM SPT Switchover Receiver RP Source 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

36. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 36 PIM-SM SPT Switchover Receiver RP Source 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

37. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 37 PIM-SM SPT Switchover Receiver RP Source 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

38. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 38 PIM-SM SPT Switchover Receiver RP Source 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

39. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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

40. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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

41. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 41 Multiple RPs with Auto RP PIM Sparse-Dense-Mode

42. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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.

43. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI 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.

44. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 44 Q and A

45. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 45 Resources  Internet Protocol IP Multicast Technology http://www.cisco.com/en/US/tech/tk828/tech_brief09186a00800 a4415.html  IP Multicast Deployment Fundamentals http://www.cisco.com/en/US/tech/tk828/tech_brief09186a00800 e9952.html  Cisco IOS Multicast Q&A http://www.cisco.com/en/US/tech/tk828/technologies_q_and_a_ item09186a00801bb25d.shtml

46. © 2006 Cisco Systems, Inc. All rights reserved.Cisco Public BSCI Module 7 Lesson 3 46