IP Multicast: Does It Really Work? Wayne M. Pecena, CPBE, CBNE Texas A&M Information Technology Educational Broadcast Services - KAMU v2
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 2
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 The OSI Model DoD Model TCP/IP Model Encapsulation 7 Application Service Provided to Applications 6 Presentation Provides Data Formatting 4 Application Application Data 5 Session Provides Conversation Control 4 Transport Provides Data Sequencing, Flow Control, Integrity 3 Transport TCP UDP Segments 3 Network Provides Logical Addressing, Fragmentation, End-End Delivery 2 Internetwork IP Packets 2 1 Data Link Physical LLC MAC Provides Physical Addressing, Error Correction Provides Media Interface, Topology 1 Network Access Network Interface Frames Bits 4
Layer 2 Standards: Project 802 Ethernet Standards: 802.1 Bridging 802.3 Ethernet 802.11 Wireless http://standards.ieee.org/about/get/ 5
Layer 3 Standards: Request for Comments RFC s The Standards Bible of the Internet Explains All Aspects of IP Networking www.rfc-editor.org/rfc.html 6
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) Simplified Representation FF:FF:FF:FF:FF:FF 00:12:3F:8D:4D:A7 172.15.1.1 172.15.2.2 DATA Trailer Destination MAC Source MAC Source IP Destination IP IP Packet Ethernet Frame
Classful Addressing: 165.95.240.136 (Implied Mask 255.255.0.0) IP Address Formats VLSM Addressing: 165.95.240.136 255.255.255.192 (Explicit Mask 255.255.255.192) 1 1 CIDR Notation : 165.95.240.136 /26 Number of Mask Bits 8
Classful IPv4 Addressing Leading Bit Patterns Indicated the Class Class First Octet Range Use A 1-126 Large Unicast Network B 128-191 Medium Unicast Network C 192-223 Small Unicast Network D 224-239 Multicast Network E 240-255 Experimental Network Octet 1 Octet 2 Octet 3 Octet 4 1 1 1 0 0 Octet 1 Class A: 1-126 Octet 1 Class D: 224-239 1 0 Octet 1 Class B: 128-191 1 1 0 Octet 1 Class C: 192-223
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 10
Routing & Switching Summary Route Between Networks (Control Broadcast Domains) Switch to Eliminate a Collision Domain Within a Broadcast Domain 11
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 12
Multicast Multicast Adds a 3 rd Packet Distribution Approach One Send Host to A Group of Receive Hosts on the Subnet A Host Must Join A Multicast Group To Receive Multicast Packets 13
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 14
Unicast Potential of 17 Sessions from the Server 15
Broadcast 16
Multicast 17
Why IP Multicast? Efficient Network Resource Use & Bandwidth Conserving Technology Eliminates Network Traffic Redundancy on Segments Provides Server & CPU Load Decrease 18
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 19
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 21
Deriving a Multicast Layer 2 Address IANA OUI for Multicast - 24 bits 01 00 5E Multicast IP Address 32 bits 223 25 229 1 00000001 00000000 01011110 11011111 00110010 11100101 00000001 Take Last 23 bits 01 00 5E 50 E5 01 00000001 00000000 01011110 00110010 11100101 00000001 Yields 48-bit Multicast MAC Address: 01:00:5E:50:E5:01 22
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 24
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) 25
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) 26
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. 27
IP Multicast Distribution Tree An IP Multicast Distribution Tree is a Path Structure From a Multicast Source to a Multicast Destination. Trim or Prune the Tree Single Source Tree Graft The Tree 28
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 29
PIM Dense Mode - PIM-DM All Segments of the Multicast Tree Are Flooded. Branches Are Pruned if Multicast Traffic is Not needed. 30
PIM Sparse Mode - PIM-SM Multicast Traffic is NOT Flooded. A Rendezvous Point is Designated. All Multicast Sources & Clients Register With the Rendezvous Point. 31
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 X Discarded 32
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 8 Bits 4 Bitsaddress 4 prefix format 112 Bits 1 1 1 1 1 1 1 1 Flag Field Scope Field Group ID f f Flag Field: Defines a Permanent Address 0 or a Transient Address 1 Scope Field: Defines the Scope of the Multicast 33
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 34
NOAA Originated Multicast to TAMU-Galveston Current Multicast Project Provided Live HD Video Images of 200 Year Old Shipwreck Artifact Recovery Effort in Gulf 35
Multicast Acronym Glossary 37
References http://www.cisco.com/en/us/docs/ios/solutions_docs/ip_multicast/white_papers/mcst_ovr.html 38
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 www.ietf.org 39
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! 40
? Questions? Thank You for Attending! Wayne M. Pecena Texas A&M University w-pecena@tamu.edu 979.845.5662