Multicasting and Multicast Routing Protocols Objectives Differentiate between

Multicasting and Multicast Routing Protocols Objectives • Differentiate between a unicast and a multicast message • Understand multicast link state routing and MOSPF • Understand the Protocol Independent Multicast Protocols TCP/IP Protocol Suite 1

UNICAST and MULTICAST A message can be unicast, multicast, or broadcast. Let us clarify these terms as they relate to the Internet. In unicast communication, there is one source and one destination. The relationship between the source and destination is one-to-one. In unicasting, the router forwards the received packet through only one of its interfaces. TCP/IP Protocol Suite 2

Multicasting In multicast communication, there is one source and a group of destinations. The relationship is one-to-many. In multicasting, the router may forward the received packet through several of its interfaces. Multicasting has many applications today such as access to distributed databases, information dissemination, teleconferencing, and distance learning. TCP/IP Protocol Suite 3

Multicasting versus multiple unicasting Emulation of multicasting through multiple unicasting is not efficient and may create long delays, particularly with a large group. TCP/IP Protocol Suite 4

Shortest path tree in unicast routing In unicast routing, each router in the domain has a table that defines a shortest path tree to possible destinations. TCP/IP Protocol Suite 5

Source-based tree approach There are two types of shortest path tree in multicast routing: sourcebased tree and group-shared tree. In the source-based tree approach, each router needs to have one shortest path tree for each group. TCP/IP Protocol Suite 6

Group-shared tree approach In the group-shared tree approach, only the core router, which has a shortest path tree for each group, is involved in multicasting. TCP/IP Protocol Suite 7

Taxonomy of common multicast protocols MOSPF: Multicast Open Shortest Path First DVMRP: Distance Vector Multicast Routing Protocol PIM: Protocol Independent Multicast No multicast router PIM-DM: PIM, Dense Mode available in today’s PIM-SM: PIM, Sparse Mode Internet CBT: Core-Based Tree TCP/IP Protocol Suite 8

Multicasting Routing Protocols MOSPF is a multicast link state routing using source-based tree approach. DVMRP is a multicast distance vector routing. The Core-Based Tree (CBT) protocol is a group-shared protocol that uses a core as the root of the tree. The autonomous system is divided into regions and a core (center router or rendezvous router) is chosen for each region. PIM-DM is used in a dense multicast environment, such as a LAN. PIM-SM is used in a sparse multicast environment such as a WAN. TCP/IP Protocol Suite 9

Summary 1. Intradomain and interdomain routing 2. Unicast routing: distance vector routing, link state, path vector routing 3. RIP, OSPF and BGP 4. RIP table update 5. Dijkstra’s shortest path algorithm to find the shortest path tree 6. Difference between multicast and unicast 7. Source-based multicast tree and group based multicast tree TCP/IP Protocol Suite 10

Excises 1. A router running RIP has a routing table with 20 entries. How many periodic timers are needed to handle this table? How many expiration timers are needed to handle this table? Suppose 5 routes are invalid, how many garbage collection timer are needed to handle this table? 2. Below is a network, using Dijkstra algorithm to find the shortest path tree of the node A and E, and construct their routing table. A 5 C 4 B TCP/IP Protocol Suite 2 E 6 2 6 8 3 D 5 F 3 2 H 4 G 11

Solutions 1. 1 periodic timer is needed. 20 expiration timer are needed 5 garbage timer are needed, each for 1 invalid entry 2. Shortest path tree for A E 9 A C 11 F H 5 B 4 TCP/IP Protocol Suite D 7 12 G 14 12

Solutions-cont. I 2. Routing table of A Node Cost Next Router A 0 - B 4 - C 5 - D 7 B E 9 B F 11 B G 12 B H 14 B TCP/IP Protocol Suite 13

Solutions-cont. II 2. Shortest path tree of E E A 9 F 2 C 6 B 5 TCP/IP Protocol Suite H D 2 5 G 4 14

Solutions-cont. III 2. Routing table of A Node Cost Next Router A 9 D B 5 D C 6 - D 2 - E 0 - F 2 - G 4 F H 5 F TCP/IP Protocol Suite 15