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- Multicast Routing- Network IRL

Jens A Andersson

Multicast: one sender to many (not all) receivers

•Unicast: act of sending a datagram to one and only one receiver•Multicast: act of sending a datagram to multiple receivers with single “transmit” operation

♦ analogy: one teacher to many students but only to those who are taking the course

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Multicast: one sender to many receivers

“Multicast” via Unicast

multicast receiver (red)

not a multicast receiver (red)

routersforward unicastdatagrams

Multicast: one sender to many receivers

Network multicast

Multicastrouters (red) duplicate and forward multicast datagrams

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Figure 21.23 Multicasting

Source and Group (S,G)

Joining a mcast group: two-step process

local: host informs local mcast router of desire to join group: IGMP (Internet Group Management Protocol)

wide area: local router interacts with other routers to receive mcast datagram flow and build forwarding tree♦many protocols (e.g., DVMRP, MOSPF, PIM)

IGMPIGMP

IGMP

wide-areamulticast

routing

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Figure 21.24 IGMP message types

IGMP Message Types

Figure 21.26 IGMP operation

IGMP operation

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Figure 21.27 Membership report

IGMP Membership Report

0x16

No Response

IGMP Leave report

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No Response

IGMP General Query

Mcast forwarding

Unicast forwarding done according to destinationMulticast routing done according to source

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Figure 21.34 Reverse path forwarding

RPF

Scope = individual router

Figure 21.35 RPF versus RPB

RPB

Scope = all routers from source to destination

Build tree from source to destinationsEach destination has one single parent

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Figure 21.36 RPF, RPB, and RPM

RPM

Tree scaping mechanism added

Multicast/RPM is Tree Building

Source-Based TreeGroup-Shared Tree

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Source-Based Tree,One Tree Per Source

R1

S1

R2

S2

R4

R3

Group Shared Tree,Shared by All Sources

R1

S1

R2

S2

R4

R3

Rendezvous Point

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Figure 21.39 Sending a multicast packet to the rendezvous router

Tunnelling from source to RP

Figure 21.33 Multicast routing protocols

Multicast Routing Protocols

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DVMRP

• used in MBONE (overlay test net)• mcast version of RIP• forwarding decision made based on source address:

RFP

Figure 21.32 MBONE

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MOSPF

• mcast version of OSPF• use unicast database

Note! OSPF database not the same as routing table!

• each router builds least cost mcast tree with root = source

MBGP

• mcast version of BGP• builds special mcast routing table that spans ASes

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CBT

• Core/Centre Based Tree• compare group-shared tree• access router sends join to RP (unicast)• intermediate routers eavesdrops join message• Forwarding tree built from leaves!

PIM

• Unicast Protocol Independent• uses whatever available routing info for RPF

lookups• two modes:

♦Sparse Mode♦Dense Mode

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PIM SM

• trees are built on demand from listeners• compare CBT• group-shared trees with rendez-vous points• grafting/pruning• can switch from group-shared to source-based if

more efficient

PIM DM

• hypothesis: all hosts are listeners• build source-based tree from source• routers without listeners prunes tree

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Example Topologyg g

s

g

Phase 1: Truncated Broadcastg g

s

g

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Phase 2: Pruningg g

s

prune (s,g)

prune (s,g)

g

Steady Stateg g

s

g

g

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graft (s,g)

graft (s,g)

Grafting on New Receiversg g

s

g

greport (g)

Steady State after Graftingg g

s

g

g

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What else?• How to cross borders?• How find active groups?

♦Session Directory

• How limit group scope?♦Filter group addresses at border routers

Local groupsRegional groupsGlobal groups

• “Mcast on demand”? ♦Delayed mcast

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Network IRL

♦Design issues ( my empirical findings)♦Some examples

GLIFNordUNETSUNETLUNETSmall enterpriceHome

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Design Goals♦Service Quality

AvailabilityCapacity (“Bandwidth”)Delay, jitterPacket loss

♦QoSTraffic prioritising

♦ResilienceRedundancy (“L0”, L1, L2, L3)

♦Administrative, Organisational

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Constraints♦ Technical

Compare Design GoalsLimit size of broadcast domains!Number of broadcast domains = routes

♦ GeographicalInter node distancesPhysical redundancy

♦ Economical♦ Security

What can be open, what has to be limited access?Is it my responsibility?

♦ AdministrativeAdapt broadcast domains to organisational boundariesResponsibilities/Boundries

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End-to-end performance

ISP X

ISP Y ISP Z

The user perspective!

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Establish Boundaries

♦Technical♦Administrative/Organisational♦Legible, Apparent

♦Boundaries must coincide!

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GLIF(Global Lambda Integrated Facility)

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NORDUnet

• Northern Light

• IP network

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OptoSUNET

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OptoSUNET♦2 * 1, 10 Gbps to universities♦Hybrid network

Native IP/InternetWavelengths/DWDM < 40 Gbps/colour)

♦FibreTDC Song

♦Active equipmentOwned by SUNETJuniper/Ciena

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OptoSUNET

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LUNET:Fibre network in Lund

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GigaLUNET

Goals:♦Adaptable to organisational changes♦Effective operation and management♦Operational QoS♦High availability♦ Increased capacity♦Extremely low recover time approx 50ms

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GigaLUNET

♦10 Gbps in Core and Centralized Distribution♦1 – 10 Gbps in Decentralized Distribution and Access♦Single Mode Fibre♦Active Equipment: Extreme Networks♦EAPS in L2 (Distribution)♦Equal Path Cost in L3 (Core)

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GigaLUNET design

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Smaller Enterprice Network

♦Data securityProtect intra networkDMZ for customer serversVPN

♦Single connection to ISPLimited routable IP address space

• Private address space on intranet

♦Several broadcast domainsSecurity

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Design

ISP

FW + NAT

Main switch

Hosting(DMZ)

Clients

Servers

WLAN

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Home Network

ISP

FW + NAT(server,WLAN)

Main switch

Wired and/or WLAN