1 Computer Networks IP Multicast

2 Recall Unicast Broadcast Multicast sends to a specific group

3 Unicast

4 Multicast

5 Introduction to IP Multicast Class D group address ( x.x.x) First bits must be 1110 of first octet How to join/leave a multicast group? How to map to hardware address? How to route to a IP multicast group?

6 IP Multicast Addressing Some reserved addresses /24 Link local reserved e.g RIPv2 routers /8 Private (Administratively Scoped) IP Multicast to ethernet multicast mapping place low-order 23 bits of IP address into low- order 23 bits of special Ethernet address 01:00:5e:00:00:00 problem... IP multicast has 28 significant bits!

7 Internet Group Multicast Protocol (IGMP) Standardized in RFC 1112 and 2236 Host/Router signalling protocol Hosts send IGMP join messages Router periodically queries IGMPv3 in draft Hosts only listen to specific group sources

8 Multicast routing Backwards from unicast routing Reverse Path Forwarding (RFP) Route away from source Could follow the shortest (source tree) path Could build a shared distribution tree Rendevous Point (RP) Dense (Push) and Sparse (Pull) Modes

9 Distance Vector Multicast Routing Protocol (DVMRP) Similar to RIP Infinity = 32 hops Flood and Prune builds distribution tree Grafting adds back a link Was widely used in early MBONE Does not scale

10 Multicast OSPF (MOSPF) LSAs carry multicast route information Each router learns entire multicast tree Only works with OSPF networks Does not scale well Not popular

11 Protocol Independent Multicast Dense Mode (PIM-DM) Uses any underlying routing protocol e.g. RIP, OSPF, IS-IS, BGP, etc. Very similar to DVMRP Floods and prunes back based on membership Does not scale to large networks (MBONE)

12 Protocol Independent Multicast Sparse Mode (PIM-SM) Supports source and shared trees Uses a Rendevous Point (RP) Can use any underlying routing protocol Traffic only sent down joined branches Can dynamically switch to optimal source tree depending on traffic pattern

13 PIM-SM Illustrated

14 Internet MBONE Multicast backbone overlay on the Internet Originally used DVMRP, now mostly uses PIM-SM Few commercial organizations using it Many educational and research institutions using it

15 Common MBONE Tools SDR VAT/RAT VIC WB IP/TV Mtrace