TDC375 Autumn 03/04 John Kristoff - DePaul University 1 Network Protocols Multicast

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 Recall Unicast Broadcast Multicast Unicast source address Group destination address (class D)

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 Unicast one-to-one

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 Multicast one-to-many

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 Multicast operation questions How do routers route/forward these packets? How do interested receivers learn about groups? How do hosts join (and leave) groups? What would be the MAC destination address? What about security and reliability?

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 IP multicast addressing /4 (first 4 bits always 1110) Registered, reserved and special use addresses e.g /24 – link local /8 – GLOP addresses IP to Ethernet MAC layer address mapping IANA OUI = 00:00:5e (01:00:5e for multicast) Map 23 low order IP bits to last 23 MAC bits Yes, there is a mismatch (overlap of groups)

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 Internet group management protocol (IGMP) Host to router link layer signalling protocol Hosts issue join/leave to signal interest or not Routers use IGMP to build forwarding state IGMPv1 - 1 st generation, joins and queries IGMPv2 – hosts can send explicit leave messages IGMPv3 – hosts selectively specify sources Required for source-specific multicast (SSM) IGMPv3 not widely implemented yet

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 IGMP packet format

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 Multicast routing Broadcast and prune (DVMRP, PIM-DM) Reverse shortest path tree Routers do reverse path forwarding (RPF) check Explicit join (CBT, PIM-SM) Receivers send join to rendezvous point (RP) Senders send multicast data to RP, up the tree RP fans out multicast data (its a meeting point) Optimizations in PIM-SM to short-cut the RP Shared tree versus source specific tree

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 Distance vector multicast routing protocol (DVMRP) Similar to RIP Infinity = 32 hops Flood everywhere first, prune back if necessary Graft back leaf nodes if necessary, requires state 1 st generation multicast/MBONE – deprecated Relatively poor scaling properties PIM-DM is similar Useful for dense population of group members

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 Protocol independent multicast – sparse mode (PIM-SM) Underlying unicast routing protocol is used Receivers must explictly join groups (no flooding) Everyone meets at a rendezvous point (RP) RP is the core of a uni-directional tree First hop routers encapsulate multicast to RP RP can join source to the tree to avoid encap State and reliability issues

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 PIM-SM illustrated

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 Multi-protocol BGP (MBGP) BGP extension to carry other routes (e.g multicast) Provides for route aggregation and policy Used between ASes Carries information about the sources of multicast

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 Multicast source discovery protocol (MSDP) A way for receivers to discover groups and sources Connects PIM-SM domains together MSDP peering routers exchange SA info Source advertisements announced by senders MSDP messages are flooded to all peers State and flooding issues Widely considered to be a temporary hack...but nothing better exists yet

TDC375 Autumn 03/04 John Kristoff - DePaul University 1 Internet IP multicast From DVMRP MBONE to today's protocols Widely deployed on Internet2 and intra-domain IGMPv2/PIM-SM/MBGP/MSDP widely deployed SSM addresses some scaling/security issues DoS and state attacks still a significant risk Common tools and applications deployed IP/TV, sdr, mtrace, beacons, NUTV, on-the-i University of Oregon has a lot of expertise