1april 16, 2002 layer 3 multicast addressing ip group addresses 224.0.0.0–239.255.255.255 “class...
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1April 16, 2002
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
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2April 16, 2002
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
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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
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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 Be Aware of the Overlap of Layer 3 Addresses to Layer 2 AddressesAddresses to Layer 2 Addresses
32 Bits
23 Bits
24 Bits 24 Bits
48 Bits
01-00-5e-7f-00-0101-00-5e-7f-00-01
239.255.0.1239.255.0.1
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5April 16, 2002
Layer 2 Multicast Addressing—(Ethernet)
Be Aware of the Overlap of Layer 3 Be Aware of the Overlap of Layer 3 Addresses to Layer 2 AddressesAddresses to Layer 2 Addresses
01-00-5e-01-01-0101-00-5e-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
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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
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7April 16, 2002
IGMPv1• RFC 1112— “Host extensions for IP
Multicasting”
– Membership QueriesQuerier sends IGMP query messages to 224.0.0.1 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 ReportsIGMP 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
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8April 16, 2002
H3
IGMPv1—Joining a Group
• Joining member sends report to 224.1.1.1 immediately upon joining
H3224.1.1.1
Report
IGMPv1
H1 H2
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9April 16, 2002
IGMPv1—General Queries
• Periodically sends General Queries to 224.0.0.1 to determine memberships
General Query to 224.0.0.1
IGMPv1
H1 H2 H3
MulticastRouter
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10April 16, 2002
IGMPv1—Maintaining a Group
IGMPv1
#1#1 Router sends periodic queries
Query to224.0.0.1 #1#1
#2#2 One member per group per subnet reports
224.1.1.1
Report#2#2
#3#3 Other members suppress reports
224.1.1.1
SuppressedX
#3#3
224.1.1.1
SuppressedX
#3#3
H1 H2 H3
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11April 16, 2002
H3
• Router sends periodic queries
Query to224.0.0.1
• Hosts silently leave group
H3
• Router continues sending periodic queries
Query to224.0.0.1
IGMPv1—Leaving a Group
IGMPv1
H1 H2
• No Reports for group received by router
• Group times out
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12April 16, 2002
IGMPv2
• RFC 2236
–Leave Group messageHost 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 queryAfter 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
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13April 16, 2002
IGMPv2 — (cont.)
– Querier election mechanismOn multiaccess networks, an IGMP Querier router iselected based on lowest IP address. Only the Querier router sends Querys.
– Query-Interval Response TimeGeneral 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
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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.
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15April 16, 2002
H2
IGMPv2—Joining a Group
• Joining member sends report to 224.1.1.1 immediately upon joining (same as IGMPv1)
H2224.1.1.1
Report
1.1.1.1
H1 H3
1.1.1.10 1.1.1.11 1.1.1.12
rtr-a
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16April 16, 2002
IGMPv2—Querier Election
IGMPv2
1.1.1.11.1.1.2
H1 H2 H3
1.1.1.10 1.1.1.11 1.1.1.12
• Intially all routers send out a Query
Query Query
• Router w/lowest IP address “elected” querier
IGMPQuerier
• Other routers become “Non-Queriers”
IGMPNon-Querier
rtr-artr-b
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17April 16, 2002
IGMPv2—Maintaining a Group
• Router sends periodic queries
Query1.1.1.1
IGMPv2
1.1.1.10 1.1.1.11 1.1.1.12
• One member per group per subnet reports
224.1.1.1
Report
• Other members suppress reports
224.1.1.1
SuppressedX
224.1.1.1
SuppressedX
H1 H2 H3
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18April 16, 2002
IGMPv2—Leaving a Group
rtr-a>sh ip igmp groupIGMP Connected Group MembershipGroup Address Interface Uptime Expires Last Reporter224.1.1.1 Ethernet0 6d17h 00:02:31 1.1.1.11
1.1.1.1
H1 H2 H3
1.1.1.10 1.1.1.11 1.1.1.12
rtr-a
IGMP State in “rtr-a” before Leave
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19April 16, 2002
IGMPv2—Leaving a Group
• H2 leaves group; sends Leave message
1.1.1.1
H1 H2 H3
1.1.1.10 1.1.1.11 1.1.1.12
H2
Leave to224.0.0.2
224.1.1.1
#1#1
• Router sends Group specific query
Group SpecificQuery to 224.1.1.1
#2#2
• A remaining member host sends report
Report to224.1.1.1
224.1.1.1
#3#3
• Group remains active
rtr-a
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20April 16, 2002
IGMPv2—Leaving a Group
rtr-a>sh ip igmp groupIGMP Connected Group MembershipGroup Address Interface Uptime Expires Last Reporter224.1.1.1 Ethernet0 6d17h 00:01:47 1.1.1.12
1.1.1.1
H1 H2 H3
1.1.1.10 1.1.1.11 1.1.1.12
rtr-a
IGMP State in “rtr-a” after H2 Leaves
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21April 16, 2002
IGMPv2—Leaving a Group
• Last host leaves group; sends Leave message
1.1.1.1
H1 H3
1.1.1.10 1.1.1.11 1.1.1.12
H3
Leave to224.0.0.2
224.1.1.1
#1#1
• Router sends Group specific query
Group SpecificQuery to 224.1.1.1
#2#2
• No report is received• Group times out
rtr-a
H2
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22April 16, 2002
IGMPv2—Leaving a Group
rtr-a>sh ip igmp groupIGMP Connected Group MembershipGroup Address Interface Uptime Expires Last Reporter
1.1.1.1
H1 H2 H3
1.1.1.10 1.1.1.11 1.1.1.12
rtr-a
IGMP State in “rtr-a” after H3 Leaves
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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
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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 ReportsIGMP Leave Messages
• Impact on Switch : Must process ALL layer 2 Mcast packets
Admin. load increases w/Mcast traffic loadRequires special h/w to maintain throughput
PIM
IGMP
IGMP Snooping
IGMP
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1
2
MAC Address Port0000.6503.1d0e 5
0
Host-1
Router-A
3
Host-2
4
Host-3
5
Host-4(0000.6503.1d0e)
CAMTableCAMTable
Switching EngineCPUCPU
LAN Switch
Typical L2 Switch Architecture
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1
2
MAC Address Ports
IGMP Report224.1.2.3
IGMP Report224.1.2.3
0
Host-1
Router-A
3
Host-2
4
Host-3
5
Host-4
CAMTableCAMTable
Switching EngineCPUCPU
LAN Switch
IGMP Snooping — 1st Join
0100.5e01.0203 0,1,2
Entry Added
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LAN Switch
CAMTableCAMTable
1
2
MAC Address Ports 0100.5e01.0203 0,1,2
IGMP Report224.1.2.3
IGMP Report224.1.2.3
0CPUCPU
Host-1
Router-A
3
Host-2
4
Host-3
5
Host-4
Switching Engine
IGMP Snooping — 2nd Join
,5
Port Added
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LAN Switch
CAMTableCAMTable
1
2
0CPUCPU
Host-1
Router-A
3
Host-2
4
Host-3
5
Host-4
Switching Engine(w/L3 ASICs)
IGMP Leave Group224.1.2.3
(0100.5e00.0002)
IGMP Leave Group224.1.2.3
(0100.5e00.0002)
MAC Address L3 Ports 0100.5e00.00xx IGMP 00100.5e01.0203 IGMP 00100.5e01.0203 !IGMP 1,2,5
IGMP Snooping — Leaves
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LAN Switch
CAMTableCAMTable
1
2
0CPUCPU
Host-1
Router-A
3
Host-2
4
Host-3
5
Host-4
Switching Engine(w/L3 ASICs)
IGMP General Query224.0.0.1
(0100.5e00.0001)
IGMP General Query224.0.0.1
(0100.5e00.0001)
MAC Address L3 Ports 0100.5e00.00xx IGMP 00100.5e01.0203 IGMP 00100.5e01.0203 !IGMP 1,2,5
IGMP Snooping — Leaves (cont.)
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LAN Switch
CAMTableCAMTable
1
2
0CPUCPU
Host-1
Router-A
3
Host-2
4
Host-3
5
Host-4
Switching Engine(w/L3 ASICs)
IGMP Leave Group224.1.2.3
(0100.5e00.0002)
IGMP Leave Group224.1.2.3
(0100.5e00.0002)
MAC Address L3 Ports 0100.5e00.00xx IGMP 00100.5e01.0203 IGMP 00100.5e01.0203 !IGMP 1,5
IGMP Snooping — Leaves
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LAN Switch
CAMTableCAMTable
1
2
0CPUCPU
Host-1
Router-A
3
Host-2
4
Host-3
5
Host-4
Switching Engine(w/L3 ASICs)
IGMP Leave Group224.1.2.3
(0100.5e01.0203)
IGMP Leave Group224.1.2.3
(0100.5e01.0203)
MAC Address L3 Ports 0100.5e00.00xx IGMP 00100.5e01.0203 IGMP 00100.5e01.0203 !IGMP 1,5
IGMP Snooping — Leaves
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LAN Switch
CAMTableCAMTable
1
2
0CPUCPU
Host-1
Router-A
3
Host-2
4
Host-3
5
Host-4
Switching Engine(w/L3 ASICs)
MAC Address L3 Ports 0100.5e00.00xx IGMP 0
IGMP General Query224.0.0.1
(0100.5e00.0001)
IGMP General Query224.0.0.1
(0100.5e00.0001)
IGMP Snooping — Leaves
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LAN Switch
CAMTableCAMTable
1
2
0CPUCPU
Host-1
Router-A
3
Host-2
4
Host-3
5
Host-4
Switching Engine(w/L3 ASICs)
IGMP Leave Group224.1.2.3
(0100.5e00.0002)
IGMP Leave Group224.1.2.3
(0100.5e00.0002)
MAC Address L3 Ports 0100.5e00.00xx IGMP 0
IGMP Snooping — Leaves
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34April 16, 2002
VideoServer
Unnecessary Traffic!!!Unnecessary Traffic!!!Unnecessary Traffic!!!Unnecessary Traffic!!!
VLAN1 VLAN2 VLAN3
Design Issue - Server Location
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35April 16, 2002
VideoServer
VLAN1 VLAN2 VLAN3
Design Issue - Server Location
Keep high B/W sources close to router.
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36April 16, 2002
ReceiverGroup 2
ReceiverGroup 1
T1 WAN
VideoServer
1.5MBMPEGVideo
Streams
UnnecessaryUnnecessaryMulticastMulticastTraffic !!!Traffic !!!
UnnecessaryUnnecessaryMulticastMulticastTraffic !!!Traffic !!!
Holy Multicast, Batman!!3MB of unwanted data!(Choke, gasp, wheeze!)
Router-A
Router-B Router-C
Router-D
Design Issue - Core Switch
UnnecessaryUnnecessaryMulticastMulticastTraffic !!!Traffic !!!
UnnecessaryUnnecessaryMulticastMulticastTraffic !!!Traffic !!!
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37April 16, 2002
ReceiverGroup 2
ReceiverGroup 1
T1 WAN
VideoServer
1.5MBMPEGVideo
Streams
UnnecessaryUnnecessaryMulticastMulticastTraffic !!!Traffic !!!
UnnecessaryUnnecessaryMulticastMulticastTraffic !!!Traffic !!!
Router-A
Router-B Router-C
Router-D
Design Issue - Core Switch
Move WAN Router to another VLAN segment.
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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.
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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
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40April 16, 2002
Multicast Routing
• Dense-mode multicast routingDistance Vector Multicast Routing Protocol (DVMRP
Multicast Open Shortest Path First (MOSPF)
Protocol Independent Multicast – Dense Mode (PIM-DM)
• Sparse-mode multicast routingCore Based Trees (CBT)
Protocol Independent Multicast – Sparse Mode (PIM-SM)
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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
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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
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43April 16, 2002
Research Areas
• Scalable multicast routing
• Reliable multicast
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44April 16, 2002
Interdomain Multicast Protocols
• Multicast routing across domains: MBGP
• Multicast Source Discovery: MSDP with PIM-SM