1April 16, 2002 Layer 3 Multicast Addressing IP group addresses – “Class D” addresses = high order bits of “1110” Special reserved group addresses: – : All systems on this subnet All routers on this subnet DVMRP routers OSPF routers PIMv2 Routers

2April 16, 2002 Multicast Group Addressing Group addresses have inherent scope: -Link scope: — These are never forwarded by any router -Global scope: – Can be delivered throughout the Internet -Administrative scope: – Not forwarded beyond an organization’s network

3April 16, 2002 Multicast Packet Format Source is ALWAYS a unicast address Destination is a multicast group address Packet payload is typically UDP Need to map multicast group IP addresses to Layer 2 multicast MAC addresses Sender does NOT need to be a member of the group

4April 16, 2002 Layer 2 Multicast Addressing— (Ethernet) A Layer 3 IPmc Address Maps to a Layer 2 Multicast Address: Be Aware of the Overlap of Layer 3 Addresses to Layer 2 Addresses 32 Bits 23 Bits 24 Bits 48 Bits e-7f

5April 16, 2002 Layer 2 Multicast Addressing— (Ethernet) Be Aware of the Overlap of Layer 3 Addresses to Layer 2 Addresses e Maps to: , , , , etc. etc , , ,

6April 16, 2002 IGMP: Internet Group Management Protocol How hosts tell routers about group membership Routers solicit group membership from directly connected hosts RFC 1112 specifies first version of IGMP RFC 2236 specifies version 2 of IGMP RFC 3376 specifies version 3 of IGMP IGMP messages not forwarded by routers

7April 16, 2002 IGMPv1 RFC 1112— “Host extensions for IP Multicasting” – Membership Queries Querier sends IGMP query messages to with ttl = 1, determining what group addresses have members on that subnet One router on LAN is designated/elected to send queries, but all routers listen to the replies/reports Query interval 60–120 seconds – Membership Reports IGMP report sent by one host suppresses sending by others; sending based on random timer per group Restrict to one report per group per LAN Unsolicited reports sent by host, when it first joins the group

8April 16, 2002 H3 IGMPv1—Joining a Group Joining member sends report to immediately upon joining H Report IGMPv1 H1 H2

9April 16, 2002 IGMPv1—General Queries Periodically sends General Queries to to determine memberships General Query to IGMPv1 H1 H2H3 Multicast Router

10April 16, 2002 IGMPv1—Maintaining a Group IGMPv1 #1 Router sends periodic queries Query to #1 #2 One member per group per subnet reports Report #2 #3 Other members suppress reports Suppressed X # Suppressed X #3 H1 H2H3

11April 16, 2002 H3 Router sends periodic queries Query to Hosts silently leave group H3 Router continues sending periodic queries Query to IGMPv1—Leaving a Group IGMPv1 H1 H2 No Reports for group received by router Group times out

12April 16, 2002 IGMPv2 RFC 2236 –Leave Group message Host sends leave message if it leaves the group and is the last member (reduces leave latency in comparison to v1); sent to (all routers) – Group-specific query After Host sends Leave Group message, Router sends Group- specific queries to make sure there are no members present before stopping to forward data for the group for that subnet

13April 16, 2002 IGMPv2 — (cont.) – Querier election mechanism On multiaccess networks, an IGMP Querier router is elected based on lowest IP address. Only the Querier router sends Querys. – Query-Interval Response Time General Queries specify “Max. Response Time” which inform hosts of the maximum time within which a host must respond to General Query. (Improves burstiness of the responses.) – Backward compatible with IGMPv1

14April 16, 2002 IGMPv3 adds support for "source filtering“: ability for a system to report interest in receiving packets *only* from specific source addresses, or from *all but* specific source addresses, sent to a particular multicast address; avoid delivering multicast packets from specific sources to networks where there are no interested receivers.

15April 16, 2002 H2 IGMPv2—Joining a Group Joining member sends report to immediately upon joining (same as IGMPv1) H Report H1 H rtr-a

16April 16, 2002 IGMPv2—Querier Election IGMPv H1 H2H Intially all routers send out a Query Query Router w/lowest IP address “elected” querier IGMP Querier Other routers become “Non-Queriers” IGMP Non-Querier rtr-artr-b

17April 16, 2002 IGMPv2—Maintaining a Group Router sends periodic queries Query IGMPv One member per group per subnet reports Report Other members suppress reports Suppressed X Suppressed X H1 H2H3

18April 16, 2002 IGMPv2—Leaving a Group rtr-a>sh ip igmp group IGMP Connected Group Membership Group Address Interface Uptime Expires Last Reporter Ethernet0 6d17h 00:02: H1 H2H rtr-a IGMP State in “rtr-a” before Leave

19April 16, 2002 IGMPv2—Leaving a Group H2 leaves group; sends Leave message H1 H2 H H2 Leave to #1 Router sends Group specific query Group Specific Query to #2 A remaining member host sends report Report to #3 Group remains active rtr-a

20April 16, 2002 IGMPv2—Leaving a Group rtr-a>sh ip igmp group IGMP Connected Group Membership Group Address Interface Uptime Expires Last Reporter Ethernet0 6d17h 00:01: H1 H2H rtr-a IGMP State in “rtr-a” after H2 Leaves

21April 16, 2002 IGMPv2—Leaving a Group Last host leaves group; sends Leave message H1 H H3 Leave to #1 Router sends Group specific query Group Specific Query to #2 No report is received Group times out rtr-a H2

22April 16, 2002 IGMPv2—Leaving a Group rtr-a>sh ip igmp group IGMP Connected Group Membership Group Address Interface Uptime Expires Last Reporter H1 H2H rtr-a IGMP State in “rtr-a” after H3 Leaves

23April 16, 2002 L2 Multicast Frame Switching Typical L2 switches treat Multicast Traffic as Unknown or Broadcast and must “flood” the frame to every port. Static entries can sometimes be set to specify which ports should receive which group(s) of multicast traffic. Dynamic configuration of these entries would cut down on user administration. Multicast M PIM Problem: Layer 2 Flooding of Multicast Frames

24April 16, 2002 L2 Multicast Frame Switching Switches become “IGMP” aware. IGMP packets intercepted by the NMP or by special hardware ASICs. Switch must examine contents of IGMP messages to determine which ports want what traffic. IGMP Membership Reports IGMP Leave Messages Impact on Switch : Must process ALL layer 2 Mcast packets Admin. load increases w/Mcast traffic load Requires special h/w to maintain throughput PIM IGMP IGMP Snooping IGMP

1 2 MAC Address Port d0e 5 0 Host-1 Router-A 3 Host-2 4 Host-3 5 Host-4 ( d0e) CAM Table Switching Engine CPU LAN Switch Typical L2 Switch Architecture

1 2 MAC Address Ports IGMP Report Host-1 Router-A 3 Host-2 4 Host-3 5 Host-4 CAM Table Switching Engine CPU LAN Switch IGMP Snooping — 1st Join e ,1,2 Entry Added

LAN Switch CAM Table 1 2 MAC Address Ports e ,1,2 IGMP Report CPU Host-1 Router-A 3 Host-2 4 Host-3 5 Host-4 Switching Engine IGMP Snooping — 2nd Join,5 Port Added

LAN Switch CAM Table CPU Host-1 Router-A 3 Host-2 4 Host-3 5 Host-4 Switching Engine (w/L3 ASICs) IGMP Leave Group (0100.5e ) IGMP Leave Group (0100.5e ) MAC Address L3 Ports e00.00xxIGMP e IGMP e !IGMP1,2,5 IGMP Snooping — Leaves

LAN Switch CAM Table CPU Host-1 Router-A 3 Host-2 4 Host-3 5 Host-4 Switching Engine (w/L3 ASICs) IGMP General Query (0100.5e ) IGMP General Query (0100.5e ) MAC Address L3 Ports e00.00xxIGMP e IGMP e !IGMP1,2,5 IGMP Snooping — Leaves (cont.)

LAN Switch CAM Table CPU Host-1 Router-A 3 Host-2 4 Host-3 5 Host-4 Switching Engine (w/L3 ASICs) IGMP Leave Group (0100.5e ) IGMP Leave Group (0100.5e ) MAC Address L3 Ports e00.00xxIGMP e IGMP e !IGMP1,5 IGMP Snooping — Leaves

LAN Switch CAM Table CPU Host-1 Router-A 3 Host-2 4 Host-3 5 Host-4 Switching Engine (w/L3 ASICs) IGMP Leave Group (0100.5e ) IGMP Leave Group (0100.5e ) MAC Address L3 Ports e00.00xxIGMP e IGMP e !IGMP1,5 IGMP Snooping — Leaves

LAN Switch CAM Table CPU Host-1 Router-A 3 Host-2 4 Host-3 5 Host-4 Switching Engine (w/L3 ASICs) MAC Address L3 Ports e00.00xxIGMP0 IGMP General Query (0100.5e ) IGMP General Query (0100.5e ) IGMP Snooping — Leaves

LAN Switch CAM Table CPU Host-1 Router-A 3 Host-2 4 Host-3 5 Host-4 Switching Engine (w/L3 ASICs) IGMP Leave Group (0100.5e ) IGMP Leave Group (0100.5e ) MAC Address L3 Ports e00.00xxIGMP0 IGMP Snooping — Leaves

34April 16, 2002 Video Server Unnecessary Traffic!!! VLAN1VLAN2VLAN3 Design Issue - Server Location

35April 16, 2002 Video Server VLAN1VLAN2VLAN3 Design Issue - Server Location Keep high B/W sources close to router.

36April 16, 2002 Receiver Group 2 Receiver Group 1 T1 WAN Video Server 1.5MB MPEG Video StreamsUnnecessary Multicast Traffic !!! Unnecessary Holy Multicast, Batman!! 3MB of unwanted data! (Choke, gasp, wheeze!) Router-A Router-BRouter-C Router-D Design Issue - Core Switch Unnecessary Multicast Traffic !!! Unnecessary

37April 16, 2002 Receiver Group 2 Receiver Group 1 T1 WAN Video Server 1.5MB MPEG Video Streams Unnecessary Multicast Traffic !!! Unnecessary Router-A Router-BRouter-C Router-D Design Issue - Core Switch Move WAN Router to another VLAN segment.

38April 16, 2002 IGMP Summary IGMP Snooping – Requires special “Layer-3-aware” ASICs – Increases cost of switch Design Issues – Pay attention to Campus topology – IGMP Snooping can’t solve all L2 Flooding issues.

39April 16, 2002 Multicast Routing Multicast routing is backwards from Unicast routing Unicast Routing is concerned about where the packet is going Multicast routing is concerned about where the packet came from Multicast routing uses “Reverse-Path Forwarding” A router forwards a multicast datagram only if received on the up stream interface to the source

40April 16, 2002 Multicast Routing Dense-mode multicast routing Distance Vector Multicast Routing Protocol (DVMRP Multicast Open Shortest Path First (MOSPF) Protocol Independent Multicast – Dense Mode (PIM- DM) Sparse-mode multicast routing Core Based Trees (CBT) Protocol Independent Multicast – Sparse Mode (PIM- SM)

41April 16, 2002 DVMRP Summary First datagram for any (source,group) pair is delivered to all leaf routers Leaf routers with no group members on their subnetworks send prune messages back towards the source Ultimately results in source specific shortest path tree with all leaf routers with group members After a period of time the pruned brances graft back and the next datagram is forwarded to the leaves Routers can send graft messages to quickly graft pruned brances

42April 16, 2002 PIM Sparse Mode Summary A part of Class D multicast address space has been reserved for PIM-SM Each PIM-SM group has a primary RP and a small ordered set of alternative RPs A PIM router has the option to switch to source rooted shortest path tree based on local policy PIM-SM requires routers to maintain significant state information Deployment of PIM-SM requires tight co- ordination among ISPs

43April 16, 2002 Research Areas Scalable multicast routing Reliable multicast

44April 16, 2002 Interdomain Multicast Protocols Multicast routing across domains: MBGP Multicast Source Discovery: MSDP with PIM-SM