IP Multicast: Does It Really Work?

Wayne M. Pecena, CPBE, CBNE

Texas A&M Information Technology Educational Broadcast Services - KAMU

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Agenda • Introduction • IP Networking Review • The Multicast Group • Multicast Addressing

– Layer 2 Address – Class D Layer 3 Address

• Multicast Switching & Routing • A Deployment Example • Acronym Glossary • Reference Documents • Takeaway Summary – Q&A

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5 Things Required To Build a Network • Send Host • Receive Host • Message or Data to Send Between Hosts • Media to Interconnect Hosts • Protocol to Define How Data is Transferred

Reference Models

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Application

Session

Presentation

Transport

Physical

Data Link

Network

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5

6

4

1

2

3

Transport

Internetwork

Network AccessProvides Media

Interface, Topology

Provides Data Sequencing, Flow Control, Integrity

Provides Logical Addressing, Fragmentation,

End-End Delivery

Provides Physical Addressing, Error

Correction

Service Provided to Applications

Provides Conversation Control

Provides Data Formatting

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1

2

LLC

MAC

The OSI Model TCP/IP Model Encapsulation

Application4

IP

Network Interface

TCP UDP

Application Data

Segments

Bits

Frames

Packets

DoD Model

Layer 2 Standards: • Project 802 Ethernet Standards:

– 802.1 Bridging – 802.3 Ethernet – 802.11 Wireless

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http://standards.ieee.org/about/get/

Layer 3 Standards:

• Request for Comments – RFC’s – The “Standards Bible” of the Internet – Explains All Aspects of IP Networking

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www.rfc-editor.org/rfc.html

Host Addressing • Each Host on an Ethernet Based IP Network Has: • An Unique MAC Address

– Layer 2 Physical Address (local network segment) – 48 bits

• An Unique IP Address – Layer 3 Logical Address (global routed) – 32 bits (IPv4)

172.15.1.1 172.15.2.2 DATA Trailer00:12:3F:8D:4D:A7FF:FF:FF:FF:FF:FF

DestinationMAC

SourceMAC

DestinationIP

SourceIP

IP Packet

Ethernet Frame

Simplified Representation

IP Address Formats

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Classful Addressing: 165.95.240.136 (Implied Mask 255.255.0.0) VLSM Addressing: 165.95.240.136 255.255.255.192 (Explicit Mask 255.255.255.192) CIDR Notation : 165.95.240.136 /26

Number of Mask Bits

1 1

Classful IPv4 Addressing

Class First Octet Range Use

A

E

D

C

B

240 - 255

224 - 239

192 - 223

128 - 191

1 - 126 Large Unicast Network

Experimental Network

Multicast Network

Small Unicast Network

Medium Unicast Network

Octet 1 Octet 2 Octet 3 Octet 4

0Octet 1

1 0Octet 1

1 01Octet 1

Class A: 1 - 126

Class C: 192 - 223

Class B: 128 - 191

Leading Bit Patterns Indicated the Class

1 011

Octet 1

Class D: 224-239

TCP vs UDP TCP

• Connection Oriented • Guaranteed Delivery • Acknowledgments Sent • Reliable, But Higher Latency • Segments & Sequences Data • Resends Dropped Segments • Provides Flow Control • Performs CRC • Uses Port Numbers for Multiplexing

UDP • Connectionless • Not Guaranteed • No Acknowledgements • Unreliable, But Low Latency • No Sequencing • No Retransmission • No Flow Control • Performs CRC • Uses Port Numbers for Multiplexing

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Routing & Switching Summary

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Route Between Networks (Control Broadcast Domains)

Switch to Eliminate a Collision Domain Within a

Broadcast Domain

Multicast Introduction • IP Networking is Founded on an “Unicast” Model

– One Send Host to One Receive Host

• Or the “Broadcast” Model – One Send Host to All Other Hosts on the Subnet

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Multicast • Multicast Adds a 3rd Packet Distribution Approach

– One Send Host to A Group of Receive Hosts on the Subnet

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A Host Must Join A Multicast Group To Receive Multicast Packets

Types of IP Packets on an IPv4 Network • Unicast

– One Send Host TO One Receive Host • Broadcast

– One Send Host TO ALL Hosts Within the Broadcast Domain

• Multicast – One Send Host TO Specific Hosts

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Unicast

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Potential of 17 Sessions from the Server

Broadcast

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Multicast

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Why IP Multicast? • Efficient Network Resource Use & Bandwidth

Conserving Technology – Eliminates Network Traffic Redundancy on Segments

• Provides Server & CPU Load Decrease

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Key Terminology To Be Aware Of: • Multicast Group ID • Class D IP Address Space • Internet Group Management Protocol – IGMP • Multicast Distribution Tree • Protocol Independent Multicast – PIM • Reverse Path Forwarding – RPF

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Multicast Group ID

• The Multicast Group = Hosts That Want to Receive the Same Multicast

• The Multicast Group ID Identifies Each Group • A Receiving Host Must Join a Group or Groups • The Sending Host is Not Aware of the Receiving Host(s) • Thus, UDP Must Be Utilized!

IP Multicast Addressing • Layer 2 Addressing (physical address)

– 23 Bits of 48 Bit MAC Address Reserved for Multicast – By Default: A Layer 2 Switch Will Forward Multicast Packets

Out All Ports (except origin port) – To Eliminate “Flooding” – IGMP Snooping is Utilized

• IP Group Addressing (virtual address) – 28 Bits of 32 Bit IP Address Reserved for Multicast – Class D IP Address Range Reserved for Multicast

• 224.0.0.0 to 239.255.255.255 – Layer 2 Multicast Address Derived From Layer 3 IP Address

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Deriving a Multicast Layer 2 Address

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01 5E0000000001 0101111000000000

22311011111

100000001

22911100101

2500110010

01 5E0000000001 0101111000000000

0100000001

E511100101

5000110010

Yields 48-bit Multicast MAC Address:01:00:5E:50:E5:01

IANA OUI for Multicast - 24 bits Multicast IP Address – 32 bits

Take Last23 bits

IPv4 Layer 3 Address Classes

IP Group Addressing • Multicast Utilizes “Class D” Reserved IP Address Space

– 224.0.0.0 to 239.255.255.255 • Ranges Reserved Within Class D Address Space:

– 224.0.0.0 to 224.0.0.255 Local Multicast / Routing Protocol Use – 224.0.1.0 to 238.255.255.255 Public Use (Globally Scoped) – 239.0.0.0 to 239.255.255.255 Private Use (Limited Scope)

• Common Multicast Addresses: – 224.0.0.1 All Hosts on Subnet – 224.0.0.2 All Routers on Subnet – 224.0.0.5 All OSPF Routers – 224.0.0.22 IGMP Traffic

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Internet Group Management Protocol “IGMP”

• A Multicast Group is Identified by a Multicast Address • IGMP is the Protocol That Allows a Multicast Receive

Client (Host) to Send a Request to Join a Multicast Group

• Three Versions of IGMP Exist: – IGMPv1 (RFC 1112) – IGMPv2 (RFC 2236) – IGMPv3 (RFC 3376)

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IGMP Message Types • Membership “Query”

– A Request to Identify Members of a Multicast Group

• Membership “Report” – List of Members of a Multicast Group

• Leave Group – Terminates Multicast Group Membership (Disconnect)

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IGMP in More Detail • Multicast Works by Having a Multicast Source Send

Packets to a Specific Group of Host Clients That Belong to the Multicast Group.

• The Multicast Group is Assigned a Specific Multicast Address. • IGMP Provides for Host Clients to Send a “Join” Request to a

Multicast Enabled Router. • IGMP “Snooping” Allows a Layer 2 Switch to “Learn” the

Multicast MAC Address of Multicast Groups. • IGMP Snooping “Listens” to IGMP Membership Reports and

Builds a Multicast MAC Entry in the Switch Table.

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IP Multicast Distribution Tree • An IP Multicast Distribution Tree is a Path Structure

From a Multicast Source to a Multicast Destination.

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Single Source Tree

“Trim” or “Prune” the Tree

“Graft” The Tree

Protocol Independent Multicast – “PIM” • PIM is Focused on Getting Multicast Packets to the Desired Destination • PIM Creates the Multicast Tree & “Trims” the Tree • 3-Types of PIM:

– PIM Dense Mode – PIM Sparse Mode – PIM Sparse-Dense Mode (PIM-SM-DM “Cisco Proprietary”)

• Key Difference Between PIM Modes? – “How The Distribution Tree is Created”

• Which is Best? – Dense Mode Used in Large Networks – Quick Tree Creation – Sparse Mode Used in Smaller Networks – More Efficient Bandwidth Use

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PIM Dense Mode - “PIM-DM” • All Segments of the Multicast Tree Are “Flooded”. • Branches Are “Pruned” if Multicast Traffic is Not needed.

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PIM Sparse Mode - “PIM-SM” • Multicast Traffic is NOT Flooded. • A “Rendezvous Point” is Designated. • All Multicast Sources & Clients Register With the Rendezvous Point.

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Multicast Forwarding (Routing) - RFC 3704 • Unicast Routing Only Looks at the Destination Address • Multicast Traffic is Forwarded Away From the Source Host or Downstream • Reverse Path Forwarding (RPF) is Used to Prevent Loops • A Router Only Forwards Traffic Received on an Upstream Interface • RPF Check Used to Determine if an Interface is Valid

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X Discarded

What About Multicast on an IPv6 Network? • Multicast is Inherent to IPv6! • But, You Still Must:

– Build the Distribution Tree – Provide Routing Info

• Multicast IPv6 Address Format Defined by RFC 3513 – FF00::/8 address prefix format

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1 1 1 1 1 1 1 1 Scope FieldFlag Field Group ID

8 Bits 4 Bits 4 Bits 112 Bits

Flag Field: Defines a Permanent Address “0” or a Transient Address “1”

Scope Field: Defines the Scope of the Multicast

f f

Practical Applications of IP Multicast • Typical Applications:

– Audio & Video Content Distribution – Digital Signage / Corporate Communications – Stock Quote Distribution – Distance Learning

• Common Broadcast Implementation Examples: – AoIP – IPTV

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Current Multicast Project • NOAA Originated Multicast to TAMU-Galveston • Provided “Live” HD Video Images of 200 Year Old Shipwreck Artifact

Recovery Effort in Gulf

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Multicast Acronym Glossary

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References

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http://www.cisco.com/en/US/docs/ios/solutions_docs/ip_multicast/White_papers/mcst_ovr.html

Additional IETF References Internet Engineering Task Force

• RFC 1112 Host Extension for IP Multicasting • RFC 1918 Address Allocation for Private Internets • RFC 2362 PIM - SM • RFC 2365 Administratively Scoped IP Multicast • RFC 2770 GLOP Addressing • RFC 2283 Multiprotocol Extensions for BGP-4

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www.ietf.org

Takeaway Summary • IP Multicast Focused on “One to Selected Many” Communications

– Efficient Use of Network Resources – Send Host Server Resource Reduction

• IETF RFC’s Define IP Multicast Implementation • Class D IPv4 Address Space is “Reserved” for IP Multicast • IP Multicast Utilizes “UDP” Packet Delivery (not guaranteed) • Multicast “Reverse Path” Routing is the Key to Implementation • IPv6 Natively Incorporates IP Multicast • The “Commodity Internet” Does Not Support IP Multicast:

– But Internet 2 and Private Networks Do!

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Thank You for Attending! Wayne M. Pecena Texas A&M University w-pecena@tamu.edu 979.845.5662

? Questions ?