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8/8/2019 BSCI Module 7 Lesson 2 IGMP and Layer 2 Issues_edited
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BSCI Module 7
Lesson 2 1
BSCI Module 7 Lesson 2
IP Multicasting:
IGMP and Layer 2Issues
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BSCI Module 7
Lesson 2 2
Objectives
Explain the operations of IGMPv2 and how IGMPv2utilizes Join Group and Leave Group messages.
Explain the operations of IGMPv3 and how IGMPv2and IGMPv3 interoperate.
Describe the methods used to deal with multicast in aLayer 2 switching environment.
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BSCI Module 7
Lesson 2 3
IGMP Overview
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BSCI Module 7
Lesson 2 4
Internet Group Management Protocol(IGMP)
How hosts tell routers about group membership
Routers solicit group membership from directlyconnected hosts
RFC 1112 specifies IGMPv1Supported on Windows 95
RFC 2236 specifies IGMPv2
Supported on latest service pack for Windows and mostUNIX systems
RFC 3376 specifies IGMPv3
Supported in Window XP and various UNIX systems
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BSCI Module 7
Lesson 2 5
IGMPv2RFC 2236
Group-specific query
Router sends query membership message to a single group rather than all hosts (reduces traffic).
Leave group messageHost sends leave message if it leaves the group and is the lastmember (reduces leave latency in comparison to v1).
Query-interval response time
The Query router sets the maximum Query-Response time(controls burstiness and fine-tunes leave latencies).
Querier election process
IGMPv2 routers can elect the Query Router without relying onthe multicast routing protocol.
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BSCI Module 7
Lesson 2 6
IGMPv2²Joining a Group
224.1.1.1
Join Group
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BSCI Module 7
Lesson 2 7
IGMPv2²Leaving a Group
IGMPv2 has explicit Leave Group messages, whichreduces overall leave latency.
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BSCI Module 7
Lesson 2 8
IGMPv2²Leaving a Group (Cont.)
Hosts H2 and H3 are members of group 224.1.1.1.
1. H2 sends a leave message.
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BSCI Module 7
Lesson 2 9
IGMPv2²Leaving a Group (Cont.)
2. Router sends group-specific query.
KA3
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Slide 9
KA3 In the original slide the screen of computer H3 was a different color to bring it to the attention of the learner. Please change the scree
color of computer H3 from the light teal color to a white.K aren A lderson, 10/19/2006
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BSCI Module 7
Lesson 2 10
IGMPv2²Leaving a Group (Cont.)
3. A remaining member host sends report, so group remains active.
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BSCI Module 7
Lesson 2 11
IGMPv2²Leaving a Group (Cont.)
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BSCI Module 7
Lesson 2 12
IGMPv2²Leaving a Group (Cont.)
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BSCI Module 7
Lesson 2 13
IGMPv3²Joining a Group
Joining member sends IGMPv3 report to 224.0.0.22immediately upon joining.
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BSCI Module 7
Lesson 2 14
IGMPv3²Joining Specific Source(s)
IGMPv3 Report contains desired sources in theInclude list. Only ³Included´ sources are joined.
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BSCI Module 7
Lesson 2 15
IGMPv3²Maintaining State
Router sends periodic queries:
All IGMPv3 members respond.
Reports contain multiple group state records.
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BSCI Module 7
Lesson 2 16
Self Check
1. What is the primary pur pose of IGMP?
2. When 2 IGMP routers are located on the sameEthernet segment, which router will be the designated
querier?
3. What does the ICMPv2 Query router do when itreceives a Leave Message?
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BSCI Module 7
Lesson 2 17
IGMP Layer 2Issues
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BSCI Module 7
Lesson 2 18
Determining IGMP Version Running
Determining which IGMP version is running on an
interface.
rtr-a> show ip igmp interface e0
Ethernet0 is up, line protocol is up
Internet address is 1.1.1.1, subnet mask is 255.255.255.0
IGMP is enabled on interface
Current IGMP version is 2
CGMP is disabled on interface
IGMP query interval is 60 seconds
IGMP querier timeout is 120 seconds
IGMP max query response time is 10 seconds
Inbound IGMP access group is not set
Multicast routing is enabled on interface
Multicast TTL threshold is 0
Multicast designated router (DR) is 1.1.1.1 (this system)
IGMP querying router is 1.1.1.1 (this system)
Multicast groups joined: 224.0.1.40 224.2.127.254
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BSCI Module 7
Lesson 2 19
Layer 2 Multicast Frame Switching
Problem: Layer 2 flooding of multicast
frames
Typical Layer 2 switches treatmulticast traffic as unknown or broadcast and must flood the frameto every port (in VLAN).
Static entries may sometimes be setto specify which ports receive which
groups of multicast traffic.
Dynamic configuration of theseentries may reduce administration.
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BSCI Module 7
Lesson 2 20
Layer 2 Multicast Switching Solutions
Cisco Group Management Protocol (CGMP): Simple,proprietary; routers and switches
IGMP snooping: Complex, standardized, proprietary
implementations; switches only
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BSCI Module 7
Lesson 2 21
Layer 2 Multicast Frame SwitchingCGMP
Solution 1: CGMP
Runs on switches and routers.
CGMP packets sent by routers toswitches at the CGMP multicast MACaddress of 0100.0cdd.dddd.
CGMP packet contains:
Type field: join or leave
MAC address of the IGMP client
Multicast MAC address of the group
Switch uses CGMP packet information toadd or remove an entry for a particular multicast MAC address.
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BSCI Module 7
Lesson 2 22
IGMP Snooping
Solution 2: IGMP snooping
Switches become IGMP-aware.
IGMP packets are intercepted by the CPU or byspecial hardware ASICs.
Switch examines contents of IGMP messages to learnwhich ports want what traffic.
Effect on switch without Layer 3-awareHardware/ASICs
Must process all Layer 2 multicast packets
Administration load increased with multicast trafficload
Effect on switch with Layer 3-aware Hardware/ASICs
Maintain high-throughput performance but cost of
switch increases
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BSCI Module 7
Lesson 2 23
Impact of IGMPv3 on IGMP Snooping
IGMPv3 Reports are sent to a separate group (224.0.0.22)reduces load on switch CPU
No Report Suppression in IGMPv3
IGMP Snooping should not cause a seriousperformance problem once IGMPv3 is implemented.
IGMPv3 and IGMP Snooping
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BSCI Module 7
Lesson 2 24
Self Check
1. What command is used to determine the version of IGMP active on an interface?
2. How does a typical layer 2 switch treat multicast
traffic?
3. What is CGMP?
4. What type of switch is recommending for use withIGMP snooping?
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BSCI Module 7
Lesson 2 25
Summary
IGMPv2 is a protocol used by multicast clients to join amulticast group.
IGMPv3 allows a receiver to specify a source.
If controls such as CGMP and IGMP snooping are notadded at the Ethernet switching level, all multicastframes are flooded.
CGMP is a Cisco proprietary protocol used toimplement multicast efficiently.
IGMP snooping is a standard protocol that has afunction similar to CGMP.
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BSCI Module 7
Lesson 2 26
Q and A
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BSCI Module 7
Lesson 2 27
Resources
Wikipedia IGMP article
http://en.wikipedia.org/wiki/IGMP
Multicast in a Campus Network: CGMP and IGMPSnooping
http://www.cisco.com/war p/public/473/22.html
IP Multicast Glossary of Terms
http://www.cisco.com/en/US/tech/tk828/tech_brief0900aecd801
bca26.html
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BSCI Module 7
Lesson 2 28