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Layer 3 Multicast Addressing . IP group addresses 224.0.0.0–239.255.255.255 “Class D” addresses = high order bits of “1110” Special reserved group addresses: 224.0.0.0–224.0.0.255: 224.0.0.1 All systems on this subnet 224.0.0.2 All routers on this subnet 224.0.0.4 DVMRP routers

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layer 3 multicast addressing
Layer 3 Multicast Addressing
  • IP group addresses 224.0.0.0–239.255.255.255
  • “Class D” addresses = high order bits of “1110”
  • Special reserved group addresses: 224.0.0.0–224.0.0.255:
    • 224.0.0.1 All systems on this subnet
    • 224.0.0.2 All routers on this subnet
    • 224.0.0.4 DVMRP routers
    • 224.0.0.5 OSPF routers
    • 224.0.0.13 PIMv2 Routers
multicast group addressing
Multicast Group Addressing
  • Group addresses have inherent scope:
    • Link scope: 224.0.0.0—224.0.0.255These are never forwarded by any router
    • Global scope: 224.0.1.0 – 238.255.255.255Can be delivered throughout the Internet
    • Administrative scope: 239.0.0.0 – 239.255.255.255Not forwarded beyond an organization’s network
multicast packet format
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
layer 2 multicast addressing ethernet
Layer 2 Multicast Addressing—(Ethernet)

A Layer 3 IPmc Address Maps to a Layer 2 Multicast Address:

32 Bits

23 Bits

239.255.0.1

01-00-5e-7f-00-01

24 Bits

24 Bits

48 Bits

Be Aware of the Overlap of Layer 3 Addresses to Layer 2 Addresses

layer 2 multicast addressing ethernet5
Layer 2 Multicast Addressing—(Ethernet)

Be Aware of the Overlap of Layer 3 Addresses to Layer 2 Addresses

01-00-5e-01-01-01

Maps to: 224.1.1.1, 224.129.1.1, 225.1.1.1, 225.129.1.1,

etc. etc. 238.1.1.1, 238.129.1.1, 239.1.1.1, 239.129.1.1

igmp internet group management protocol
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
igmpv1
IGMPv1
  • RFC 1112— “Host extensions for IP Multicasting”
    • Membership Queries
    • Querier sends IGMP query messages to 224.0.0.1 with ttl = 1, determining what group addresses have members on that subnet
    • One routeron 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
igmpv1 joining a group

224.1.1.1

H3

H3

Report

IGMPv1—Joining a Group

H2

H1

  • Joining member sends report to 224.1.1.1 immediately upon joining

IGMPv1

igmpv1 general queries

H2

H3

H1

General Query

to 224.0.0.1

IGMPv1—General Queries
  • Periodically sends General Queries to 224.0.0.1 to determine memberships

IGMPv1

MulticastRouter

igmpv1 maintaining a group

224.1.1.1

224.1.1.1

224.1.1.1

H2

H3

H1

X

X

Suppressed

Report

Suppressed

#3

#2

#3

Query to

224.0.0.1

#1

Router sends periodic queries

#1

One member per group per subnet reports

#2

Other members suppress reports

#3

IGMPv1—Maintaining a Group

IGMPv1

igmpv1 leaving a group

H3

H3

Query to

224.0.0.1

Query to

224.0.0.1

IGMPv1—Leaving a Group

H2

H1

IGMPv1

  • Router sends periodic queries
  • Hosts silently leave group
  • Router continues sending periodic queries
  • No Reports for group received by router
  • Group times out
igmpv2
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 224.0.0.2 (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
igmpv2 cont
IGMPv2 — (cont.)
  • Querier election mechanism
    • On multiaccess networks, an IGMP Querier router iselected based on lowest IP address. Only the Querier router sends Querys.
  • Query-Interval Response Time
    • General Queries specify “Max. Response Time” whichinform hosts of the maximum time within which a host must respond to General Query. (Improves burstinessof the responses.)
  • Backward compatible with IGMPv1
igmpv3
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.
igmpv2 joining a group

224.1.1.1

H2

H2

Report

IGMPv2—Joining a Group

1.1.1.10

1.1.1.11

1.1.1.12

  • Joining member sends report to 224.1.1.1 immediately upon joining (same as IGMPv1)

H3

H1

1.1.1.1

rtr-a

igmpv2 querier election

Query

Query

IGMPv2—Querier Election

1.1.1.10

1.1.1.11

1.1.1.12

H2

H3

H1

1.1.1.2

1.1.1.1

IGMP

Non-Querier

IGMP

Querier

IGMPv2

rtr-b

rtr-a

  • Intially all routers send out a Query
  • Router w/lowest IP address “elected” querier
  • Other routers become “Non-Queriers”
igmpv2 maintaining a group

224.1.1.1

224.1.1.1

224.1.1.1

H2

H3

H1

X

X

Suppressed

Report

Suppressed

Query

IGMPv2—Maintaining a Group

1.1.1.10

1.1.1.11

1.1.1.12

  • Router sends periodic queries

1.1.1.1

IGMPv2

  • One member per group per subnet reports
  • Other members suppress reports
igmpv2 leaving a group

rtr-a>sh ip igmp group

IGMP Connected Group Membership

Group Address Interface Uptime Expires Last Reporter

224.1.1.1 Ethernet0 6d17h 00:02:31 1.1.1.11

IGMPv2—Leaving a Group

1.1.1.10

1.1.1.11

1.1.1.12

H2

H3

H1

1.1.1.1

rtr-a

IGMP State in “rtr-a” before Leave

igmpv2 leaving a group19

224.1.1.1

224.1.1.1

H2

H2

Report to

224.1.1.1

Leave to

224.0.0.2

#1

#3

Group Specific

Query to 224.1.1.1

#2

IGMPv2—Leaving a Group

1.1.1.10

1.1.1.11

1.1.1.12

  • H2 leaves group; sends Leave message

H3

H1

1.1.1.1

rtr-a

  • Router sends Group specific query
  • A remaining member host sends report
  • Group remains active
igmpv2 leaving a group20

rtr-a>sh ip igmp group

IGMP Connected Group Membership

Group Address Interface Uptime Expires Last Reporter

224.1.1.1 Ethernet0 6d17h 00:01:47 1.1.1.12

IGMPv2—Leaving a Group

1.1.1.10

1.1.1.11

1.1.1.12

H2

H3

H1

1.1.1.1

rtr-a

IGMP State in “rtr-a” after H2 Leaves

igmpv2 leaving a group21

224.1.1.1

H3

Leave to

224.0.0.2

#1

Group Specific

Query to 224.1.1.1

#2

IGMPv2—Leaving a Group

1.1.1.10

1.1.1.11

1.1.1.12

H2

H3

H1

1.1.1.1

rtr-a

  • Last host leaves group; sends Leave message
  • Router sends Group specific query
  • No report is received
  • Group times out
igmpv2 leaving a group22

rtr-a>sh ip igmp group

IGMP Connected Group Membership

Group Address Interface Uptime Expires Last Reporter

IGMPv2—Leaving a Group

1.1.1.10

1.1.1.11

1.1.1.12

H2

H3

H1

1.1.1.1

rtr-a

IGMP State in “rtr-a” after H3 Leaves

l2 multicast frame switching

PIM

Multicast M

L2 Multicast Frame Switching

Problem: Layer 2 Flooding of Multicast Frames

  • 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.
l2 multicast frame switching24

PIM

L2 Multicast Frame Switching

IGMP Snooping

  • 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

IGMP

IGMP

typical l2 switch architecture
Typical L2 Switch Architecture

Router-A

1

LAN Switch

Switching Engine

CPU

0

CAMTable

2

3

4

5

MAC Address Port

0000.6503.1d0e 5

Host-4

(0000.6503.1d0e)

Host-1

Host-2

Host-3

igmp snooping 1st join

Entry Added

IGMP Snooping — 1st Join

Router-A

IGMP Report224.1.2.3

1

LAN Switch

Switching Engine

CPU

0

CAMTable

2

3

4

5

MAC Address Ports

0100.5e01.0203 0,1,2

Host-1

Host-2

Host-3

Host-4

igmp snooping 2nd join

Port Added

IGMP Snooping — 2nd Join

Router-A

IGMP Report224.1.2.3

1

LAN Switch

Switching Engine

CPU

0

CAMTable

2

3

4

5

MAC Address Ports

0100.5e01.0203 0,1,2

,5

Host-1

Host-2

Host-3

Host-4

igmp snooping leaves
IGMP Snooping — Leaves

Router-A

1

LAN Switch

Switching Engine

(w/L3 ASICs)

CPU

0

IGMP Leave Group

224.1.2.3

(0100.5e00.0002)

CAMTable

2

3

4

5

MAC Address L3 Ports

0100.5e00.00xx IGMP 0

0100.5e01.0203 IGMP 0

0100.5e01.0203 !IGMP 1,2,5

Host-1

Host-2

Host-3

Host-4

igmp snooping leaves cont
IGMP Snooping — Leaves (cont.)

Router-A

1

LAN Switch

Switching Engine

(w/L3 ASICs)

CPU

0

IGMP General Query

224.0.0.1

(0100.5e00.0001)

CAMTable

2

3

4

5

MAC Address L3 Ports

0100.5e00.00xx IGMP 0

0100.5e01.0203 IGMP 0

0100.5e01.0203 !IGMP 1,2,5

Host-1

Host-2

Host-3

Host-4

igmp snooping leaves30
IGMP Snooping — Leaves

Router-A

IGMP Leave Group

224.1.2.3

(0100.5e00.0002)

1

LAN Switch

Switching Engine

(w/L3 ASICs)

CPU

0

CAMTable

2

3

4

5

MAC Address L3 Ports

0100.5e00.00xx IGMP 0

0100.5e01.0203 IGMP 0

0100.5e01.0203 !IGMP 1,5

Host-1

Host-2

Host-3

Host-4

igmp snooping leaves31
IGMP Snooping — Leaves

Router-A

1

LAN Switch

IGMP Leave Group

224.1.2.3

(0100.5e01.0203)

Switching Engine

(w/L3 ASICs)

CPU

0

CAMTable

2

3

4

5

MAC Address L3 Ports

0100.5e00.00xx IGMP 0

0100.5e01.0203 IGMP 0

0100.5e01.0203 !IGMP 1,5

Host-1

Host-2

Host-3

Host-4

igmp snooping leaves32
IGMP Snooping — Leaves

Router-A

1

IGMP General Query

224.0.0.1

(0100.5e00.0001)

LAN Switch

Switching Engine

(w/L3 ASICs)

CPU

0

CAMTable

2

3

4

5

MAC Address L3 Ports

0100.5e00.00xx IGMP 0

Host-1

Host-2

Host-3

Host-4

slide33

IGMP Snooping — Leaves

Router-A

IGMP Leave Group

224.1.2.3

(0100.5e00.0002)

1

LAN Switch

Switching Engine

(w/L3 ASICs)

CPU

0

CAMTable

2

3

4

5

MAC Address L3 Ports

0100.5e00.00xx IGMP 0

Host-1

Host-2

Host-3

Host-4

slide35

Design Issue - Server Location

VideoServer

VLAN1

VLAN2

VLAN3

Keep high B/W sources close to router.

design issue core switch

Unnecessary

MulticastTraffic !!!

Holy Multicast, Batman!!

3MB of unwanted data!

(Choke, gasp, wheeze!)

Unnecessary

MulticastTraffic !!!

Design Issue - Core Switch

Video

Server

Router-A

1.5MB

MPEG

Video

Streams

T1

WAN

Router-D

Router-B

Router-C

Receiver

Group 1

Receiver

Group 2

design issue core switch37

Unnecessary

MulticastTraffic !!!

Design Issue - Core Switch

Video

Server

Router-A

T1

WAN

1.5MB

MPEG

Video

Streams

Router-D

Move WAN Router to

another VLAN segment.

Router-B

Router-C

Receiver

Group 1

Receiver

Group 2

igmp summary
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.
multicast routing
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
multicast routing40
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)
dvmrp summary
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
pim sparse mode summary
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
research areas
Research Areas
  • Scalable multicast routing
  • Reliable multicast
interdomain multicast protocols
Interdomain Multicast Protocols
  • Multicast routing across domains: MBGP
  • Multicast Source Discovery: MSDP with PIM-SM