NSR Fall24 Week 10 Lecture 2 PDF

Chapter 12 Multicasting And Multicast Routing Protocols TCP/IP Protocol Suite 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction...

Chapter 12 Multicasting And Multicast Routing Protocols TCP/IP Protocol Suite 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or  12-3 IGMP Multicast communication means that a sender sends a message to a group of recipients that are members of the same group. Each multicast router needs to know the list of groups that have at least one loyal member related to each interface. Collection of this type of information is done at two levels: locally and globally. The first task is done by the IGMP protocol; the second task is done by the multicast routing protocols. TCP/IP Protocol Suite 2  Figure 12.6 Position of IGMP in the network layer TCP/IP Protocol Suite 3  Note IGMP is a group management protocol. It helps a multicast router create and update a list of loyal members related to each router interface. TCP/IP Protocol Suite 4  Figure 12.7 IGMP messages TCP/IP Protocol Suite 5  Figure 12.8 Membership query message format TCP/IP Protocol Suite 6  Figure 12.9 Three forms of query messages TCP/IP Protocol Suite 7  Figure 12.10 Membership report message format TCP/IP Protocol Suite 8 TCP/IP Protocol Suite 9 Example 12.4 Figure 12.11 shows a host with three processes: S1, S2, and S3. The first process has only one record; the second and the third processes each have two records. We have used lowercase alphabet to show the source address. TCP/IP Protocol Suite 10  Figure 12.11 Socket state TCP/IP Protocol Suite 11 TCP/IP Protocol Suite 12 TCP/IP Protocol Suite 13 TCP/IP Protocol Suite 14  12-4 MULTICAST ROUTING Now we show how information collected by IGMP is disseminated to other routers using multicast routing protocols. However, we first discuss the idea of optimal routing, common in all multicast protocols. We then give an overview of multicast routing protocols. TCP/IP Protocol Suite 15  Topics Discussed in the Section  Optimal Routing: Shortest Path Trees TCP/IP Protocol Suite 16  Note In unicast routing, each router in the domain has a table that defines a shortest path tree to possible destinations. TCP/IP Protocol Suite 17  Figure 12.18 Shortest path tree in multicast routing TCP/IP Protocol Suite 18  Figure 12.19 Source-based tree approach TCP/IP Protocol Suite 19  Note In multicast routing, each involved router needs to construct a shortest path tree for each group. TCP/IP Protocol Suite 20  Note In the source-based tree approach, each router needs to have one shortest path tree for each group and source. TCP/IP Protocol Suite 21 E.g. Source-based Tree (1) TCP/IP Protocol Suite 22  E.g. Source-based Tree (2) Spanning Tree from Router C to Multicast Group TCP/IP Protocol Suite 23  Note 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 24  Figure 12.20 Group-shared tree approach TCP/IP Protocol Suite 25  Group-Shared Tree If a router receives a multicast packet, it encapsulates the packet in a unicast packet and sends it to the core router The core router removes the multicast packet from its capsule, and consults its routing table to route the packet TCP/IP Protocol Suite 26  12-4 ROUTING PROTOCOLS During the last few decades, several multicast routing protocols have emerged. Some of these protocols are extensions of unicast routing protocols; some are totally new. We discuss these protocols in the remainder of this chapter. Figure 12.21 shows the taxonomy of these protocols. TCP/IP Protocol Suite 27  Topics Discussed in the Section  Multicast Link State Routing: MOSPF  Multicast Distance Vector: DVMRP  Core-Based Tree: CBT  Protocol Independent Multicast: PIM TCP/IP Protocol Suite 28  Figure 12.21 Taxonomy of common multicast protocols TCP/IP Protocol Suite 29  Note Multicast link state routing uses the source-based tree approach. TCP/IP Protocol Suite 30  MOSPF (1) Group membership LSA is flooded throughout the AS The router calculates the shortest path trees on demand (when it receives the first multicast packet) MOSPF is a data-driven protocol; the first time an MOSPF router see a datagram with a given source and group address, the router constructs the Dijkstra shortest path tree TCP/IP Protocol Suite 31 Multicast Distance Vector Routing 4 decision-making strategies 1. Flooding 2. Reverse Path Forwarding (RPF) 3. Reverse Path Broadcasting (RPB) 4. Reverse Path Multicasting (RPM) TCP/IP Protocol Suite 32  Note Flooding broadcasts packets, but creates loops in the systems. TCP/IP Protocol Suite 33  Figure 12.22 RPF TCP/IP Protocol Suite 34  Reverse Path Forwarding (1) To prevent loops, only one copy is forwarded; the other copies are dropped. In RPF, a router forwards only the copy that has traveled the shortest path from the source to the router. The router extracts the source address of the multicast packet and consults its unicast routing table. TCP/IP Protocol Suite 35  Reverse Path Forwarding (2) If the packet has just come from the hop defined in the table, the packet has traveled the shortest path from the source to the router because the shortest path is reciprocal in unicast distance vector routing protocols. If a packet leaves the router and comes back again, it has not traveled the shortest path. TCP/IP Protocol Suite 36  Note RPF eliminates the loop in the flooding process. TCP/IP Protocol Suite 37  Figure 12.23 Problem with RPF TCP/IP Protocol Suite 38  Figure 12.24 RPF versus RPB TCP/IP Protocol Suite 39  Reverse Path Broadcasting (1) RPF guarantees that each network receives a copy of the multicast packet without formation of loops However, RPF does not guarantee that each network receives only one copy To eliminate duplication, we must define only one parent router (designated parent router) for each network TCP/IP Protocol Suite 40  Reverse Path Broadcasting (2) In RPB, for each source, the router sends the packet only out of those interfaces for which it is the designated parent The designated parent router can be the router with the shortest path to the source – Because routers periodically send updating packets to each other (in RIP), they can easily determine which router in the neighborhood has the shortest path to the source. TCP/IP Protocol Suite 41  Note RPB creates a shortest path broadcast tree from the source to each destination. It guarantees that each destination receives one and only one copy of the packet. TCP/IP Protocol Suite 42  Figure 12.25 RPF, RPB, and RPM (Src, Group ID) TCP/IP Protocol Suite 43  Reverse Path Multicasting (1) To increase efficiency, the multicast packet must reach only those networks that have active members for that particular group RPM adopts the procedures of Pruning and Grafting Pruning – The designated parent router of each network is responsible for holding the membership information (through IGMP) TCP/IP Protocol Suite 44  Reverse Path Multicasting (2) – The router sends a prune message to the upstream router so that it can prune the corresponding interface – That is, the upstream router can stop sending multicast message for this group through that interface Grafting – The graft message forces the upstream router to resume sending the multicast messages TCP/IP Protocol Suite 45  Note RPM adds pruning and grafting to RPB to create a multicast shortest path tree that supports dynamic membership changes. TCP/IP Protocol Suite 46  Note PIM-DM is used in a dense multicast environment, such as a LAN. TCP/IP Protocol Suite 47  PIM-DM It is used when there is a possibility that each router is involved in multicasting (dense mode) In this environment, the use of a protocol that broadcasts the packet is justified because almost all routers are involved in the process TCP/IP Protocol Suite 48  Note PIM-DM uses RPF and pruning/grafting strategies to handle multicasting. However, it is independent from the underlying unicast protocol. TCP/IP Protocol Suite 49  Note PIM-SM is used in a sparse multicast environment such as a WAN. TCP/IP Protocol Suite 50  Note PIM-SM is similar to CBT but uses a simpler procedure. TCP/IP Protocol Suite 51  PIM  There are two key components: state and the multicast distribution tree  State It is the information network devices must track in order for the router to know where it should send the traffic. State includes the component known as (S, G); S (multicast source), G (multicast group). TCP/IP Protocol Suite 52  Distribution Tree  The distribution tree is a path through the network used to distribute multicast traffic.  There are two types of distribution trees : shortest path (also known as source tree) Shared tree TCP/IP Protocol Suite 53  Source Distribution Tree  It is the shortest path from the source to the multicast group member.  It represents an optimal path, a source distribution tree minimizes the latency in the network.  At the same time, the multicast router must track all sources and maintain state information for each source. TCP/IP Protocol Suite 54  Shared Distribution Tree  Source trees have their root at the source, shared trees use a single common root, called a Rendezvous Point (RP) as the root of the distribution tree.  Other routers need to know the IP address of the RP router.  The RP router discovers the sources for all multicast groups. TCP/IP Protocol Suite 55  PIM-DM  PIM Dense Mode operates by initially flooding the multicast traffic for all groups out of all enabled interfaces.  Routers that do not have any interested hosts send PIM Prune messages to remove themselves from the tree.  Based on this “Flood and Prune” behavior, eventually, the traffic is only sent to the necessary routers that require the traffic. TCP/IP Protocol Suite 56  PIM-DM Flooding&Pruning TCP/IP Protocol Suite 57  PIM-SM  In PIM sparse mode no multicast traffic is forwarded unless someone requests it.  PIM-SM works via the use of an RP (Rendezvous Point).  Shared Tree (RP to Receiver) - The receiver sends an IGMP Join message to the first hop router (FHR), i.e its direct neighboring router.  FHR will then send a PIM Join to the RP. A shared tree is then built from the receiver to RP based upon (*, G). TCP/IP Protocol Suite 58  PIM-SM  Shortest Path Tree (Source to RP) - the source starts to send multicast traffic.  The FHR encapsulates the multicast packet into a PIM register message and sends via unicast to the RP router.  The RP decapsulates the packet and checks the multicast group to see if it has any state for any receivers for the multicast group. If so the RP sends a PIM Join message back towards to the source, in order to build an SPT (Shortest Path Tree) back to the source. TCP/IP Protocol Suite 59