Free Riding Multicast

Free Riding Multicast Berkeley SysLunch (10/10/06) Sylvia Ratnasamy (Intel Research) Andrey Ermolinskiy (U.C. Berkeley) Scott Shenker (U.C. Berkeley andICSI) ACM SIGCOMM 2006

Talk Outline • Introduction • Overview of the IP Multicast service model • Challenges of Multicast routing • Free Riding Multicast (FRM) • Approach overview • Overhead evaluation • Design tradeoffs • Implementation

C2 C1 C3 C4 Internet Routing – a High-Level View • Internet is a packet-switched network • Each routable entity is assigned an IP address C1: Send(Packet, C2Addr); • Routers forward packets towards their recipients • Routing protocols (BGP, OSPF) establish forwarding state in routers

Internet Routing – a High-Level View • Traditionally, Internet routing infrastructure offers a one-to-one (unicast) packet delivery service • Problem: Some applications require one-to-many packet delivery • Streaming media delivery • Digital conferencing • Online multiplayer games S G G G G

IP Multicast Service Model • In 1990, Steve Deering proposed IP Multicast • extension to the IP service model for efficient one-to-many packet delivery S • Group-based communication: • Join (IPAddr, GrpAddr); • Leave (IPAddr, GrpAddr); • Send (Packet, GrpAddr); G G G • Multicast routing problem: • Set up a dissemination tree rooted at the source with group members as leaves G

IP Multicast Routing S G G G G

New members must find tree ? join G? ? IP Multicast Routing S G G G G

? join G? ? IP Multicast Routing • New members must find tree • Tree changes with new members, sources S G G G G

New members must find tree Tree changes with new members, sources Tree changes with network failures ? join G? ? IP Multicast Routing S G G G G

New members must find tree Tree changes with new members, sources Tree changes with network failure Admin. boundaries and policies matter ? join G? ? IP Multicast Routing S G G G G

New members must find tree Tree changes with new members, sources Tree changes with network failure Admin. boundaries and policies matter Forwarding state grows with number of groups, sources ? join G? ? IP Multicast Routing S G G G G

IP Multicast – a Brief History • Extensively researched, limited deployment • Implemented in routers, supported by OS vendors • Some intra-domain/enterprise usage • Virtually no inter-domain deployment • Why? • Too complex? PIM-SM, PIM-DM, MBGP, MSDP, BGMP, IGMP, etc. • FRM goal: make inter-domain multicast simple

Talk Outline • Introduction • Overview of the IP Multicast service model • Challenges of Multicast routing • Free Riding Multicast (FRM) • Approach overview • Overhead evaluation • Design tradeoffs • Implementation

FRM Overview • Free Riding Multicast: radical restructuring of inter-domain multicast • Key design choice: decouple group membership discovery from multicast route construction • Principal trade-off: avoidance of distributed route computation at the expense of optimal efficiency

FRM Approach • Group membership discovery • Extension to BGP - augment route advertisements with group membership information

FRM Approach • Group membership discovery • Extension to BGP - augment route advertisements with group membership information • Multicast route construction • Centralized computation at the origin border router • Exploit knowledge of unicast BGP routes • Eliminate the need for a separate routing algorithm

Group Membership Discovery • Augment BGP with per-prefix group membership information AS X AS Y a.b.*.* c.d.e.* AS P AS Z T AS h.i.*.* f.g.*.* AS Q AS R AS V

Group Membership Discovery • Augment BGP with per-prefix group membership information AS X AS Y a.b.*.* c.d.e.* AS P AS Z T AS • Domain X joins G1 h.i.*.* f.g.*.* AS Q AS R AS V

a.b*.* {G1} Group Membership Discovery • Augment BGP with per-prefix group membership information AS X AS Y a.b.*.* c.d.e.* AS P AS Z T AS • Domain X joins G1 h.i.*.* f.g.*.* AS Q AS R • Border router at X re-advertises its prefix, attaches encoding of active groups AS V BGP UPDATE Dest AS Path FRM group membership a.b.*.* X {G1}

a.b*.* {G1} Group Membership Discovery • BGP disseminates membership change AS X AS Y a.b.*.* c.d.e.* • Border routers maintain membership info. as part of per-prefix state in BGP RIB AS P AS Z T AS h.i.*.* f.g.*.* AS Q AS R AS V

a.b*.* a.b*.* a.b*.* a.b*.* {G1} {G1} {G1} {G1} Group Membership Discovery • BGP disseminates membership change AS X AS Y a.b.*.* c.d.e.* • Border routers maintain membership info. as part of per-prefix state in BGP RIB AS P AS Z T AS h.i.*.* f.g.*.* AS Q AS R AS V

a.b*.* a.b*.* a.b*.* a.b*.* a.b*.* a.b*.* a.b*.* a.b*.* {G1} {G1} {G1} {G1} {G1} {G1} {G1} {G1} Group Membership Discovery • BGP disseminates membership change AS X AS Y a.b.*.* c.d.e.* • Border routers maintain membership info. as part of per-prefix state in BGP RIB AS P AS Z T AS h.i.*.* f.g.*.* AS Q AS R AS V

a.b*.* {G1} Group Membership Discovery • BGP disseminates membership change AS X AS Y a.b.*.* c.d.e.* • Border routers maintain membership info. as part of per-prefix state in BGP RIB AS P AS Z T AS h.i.*.* f.g.*.* AS Q AS R AS V

Group Membership Discovery • Domains Y and Z join G1 AS X AS Y a.b.*.* c.d.e.* AS P AS Z T AS h.i.*.* f.g.*.* AS Q AS R AS AS V V

c.d.e.* f.g.*.* {G1} {G1} Group Membership Discovery • Domains Y and Z join G1 AS X AS Y a.b.*.* c.d.e.* AS P AS Z T AS h.i.*.* f.g.*.* AS Q AS R AS V

Packet Forwarding AS X AS Y a.b.*.* c.d.e.* AS P AS Z T AS h.i.*.* f.g.*.* AS Q AS R AS V Domain V: Send(G1, Pkt)

Packet Forwarding Dissemination tree AS X AS Y a.b.*.* c.d.e.* AS P AS Z T AS h.i.*.* f.g.*.* AS Q AS R {G1 } Lookup AS V Domain V: Send(G1, Pkt)

Packet Forwarding Dissemination tree AS X AS Y a.b.*.* c.d.e.* V AS P Q AS Z T AS P h.i.*.* f.g.*.* AS Q AS R X {G1 } Lookup AS V Domain V: Send(G1, Pkt)

Packet Forwarding Dissemination tree AS X AS Y a.b.*.* c.d.e.* V AS P Q AS Z T AS P h.i.*.* f.g.*.* AS Q AS R X Y {G1 } Lookup AS V Domain V: Send(G1, Pkt)

Packet Forwarding Dissemination tree AS X AS Y a.b.*.* c.d.e.* V AS P Q R AS Z T AS P Z h.i.*.* f.g.*.* AS Q AS R X Y {G1 } Lookup AS V Domain V: Send(G1, Pkt)

G1 G1 SubtreeQ SubtreeR Packet Forwarding AS X AS Y a.b.*.* c.d.e.* V AS P Q R AS Z T AS P Z h.i.*.* f.g.*.* AS Q AS R X Y SubtreeQ SubtreeR AS V Domain V: Send(G1, Pkt) • V forwards packet to its children on the tree, attaches encoding the subtree in a “shim” header

G1 G1 SubtreeR SubtreeQ Packet Forwarding AS X AS Y a.b.*.* c.d.e.* V AS P Q R AS Z T AS P Z h.i.*.* f.g.*.* AS Q AS R X Y AS V Domain V: Send(G1, Pkt) • V forwards packet to its children on the tree, attaches encoding the subtree in a “shim” header

G1 G1 SubtreeQ SubtreeR Packet Forwarding AS X AS Y a.b.*.* c.d.e.* V AS P Q R AS Z T AS P Z h.i.*.* f.g.*.* AS Q AS R X Y AS V • Transit routers inspect FRM header, forward packet to their children on the tree Domain V: Send(G1, Pkt)

G1 G1 SubtreeQ SubtreeR Packet Forwarding AS X AS Y a.b.*.* c.d.e.* V AS P Q R AS Z T AS P Z h.i.*.* f.g.*.* No AS Q AS R X Y AS V • Transit routers inspect FRM header, forward packet to their children on the tree Domain V: Send(G1, Pkt)

G1 G1 SubtreeR SubtreeQ Packet Forwarding AS X AS Y a.b.*.* c.d.e.* V AS P Q R AS Z T AS P Z h.i.*.* f.g.*.* AS Q AS R X Y No AS V • Transit routers inspect FRM header, forward packet to their children on the tree Domain V: Send(G1, Pkt)

G1 G1 SubtreeR SubtreeQ Packet Forwarding AS X AS Y a.b.*.* c.d.e.* V AS P Q R Yes AS Z T AS P Z h.i.*.* f.g.*.* AS Q AS R X Y AS V • Transit routers inspect FRM header, forward packet to their children on the tree Domain V: Send(G1, Pkt)

G1 G1 G1 SubtreeR SubtreeQ TREE_BFQ Packet Forwarding AS X AS Y a.b.*.* c.d.e.* V AS P Q R AS Z T AS P Z h.i.*.* f.g.*.* AS Q AS R X Y AS V • Transit routers inspect FRM header, forward packet to their children on the tree Domain V: Send(G1, Pkt)

G1 SubtreeR Packet Forwarding AS X AS Y a.b.*.* c.d.e.* V AS P Q R AS Z T AS P Z h.i.*.* f.g.*.* AS Q AS R X Y AS V • Transit routers inspect FRM header, forward packet to their children on the tree Domain V: Send(G1, Pkt)

FRM Details • Encoding group membership • Simple enumeration is hard to scale • Border routers encode locally active groups using a Bloom filter • Transmit encoding using a new path attribute in BGP UPDATE message • Encoding the dissemination tree • Encode edges into a shim header using a Bloom filter • Tree computation is expensive  Border routers maintain shim header cache

Talk Outline • Introduction • Free Riding Multicast (FRM) • Approach overview • Overhead evaluation • Router storage requirements • Forwarding bandwidth overhead (in paper) • Design tradeoffs • Implementation

FRM Overhead – Router Storage AS X AS Y a.b.*.* c.d.e.* AS P Transit router AS Z T AS Transit forwarding state (per-neighbor, line card memory) h.i.*.* f.g.*.* AS Q AS R AS V Origin border router 1. Source forwarding state (per-group, line card memory) 2. Group membership state(per-prefix, BGP RIB)

Forwarding State (Source Border Router) • A -- number of groups with sources in the local domain • Zipfian group popularity with a minimum of 8 domains per group • 25 groups have members in every domain (global broadcast) 256 MB of line card memory enables fast-path forwarding for ~200000 active groups

FRM Overhead – Router Storage AS X AS Y a.b.*.* c.d.e.* AS P Transit router AS Z T AS Transit forwarding state (per-neighbor, line card memory) h.i.*.* f.g.*.* AS Q AS R AS V Origin border router 1. Source forwarding state (per-group, line card memory) 2. Group membership state(per-prefix, BGP RIB)

Group Membership State Requirements • Total of A multicast groups • Domains of prefix length phave 232-pusers • Each user chooses and joins k distinct groups from A • 10 false positives per prefix allowed 1M simultaneously active groups and 10 groups per user require~3GBof route processor memory (not on the fast path)

Free Riding Multicast