BSCI Module 7 Lesson 1 IP Multicasting: Explaining Multicast
Objectives <ul><li>Describe the IP multicast group. </li></ul><ul><li>Compare and contrast Unicast packets and multicast p...
Multicast Overview
IP Multicast Distribute information to large audiences over an IP network
Multicast Adoption Past, Present, and Future Multicast (1986-2005) 1992 1996 1997 1998 2000 2001 2002 2003 2004 2005 1986 ...
Why Multicast? <ul><li>Used when sending same data to multiple receivers </li></ul><ul><li>Better bandwidth utilization </...
Unicast vs. Multicast
Multicast Advantages <ul><li>Enhanced   efficiency : Controls network traffic and reduces server and CPU loads </li></ul><...
Other Multicast Advantages <ul><ul><li>For the equivalent amount of multicast traffic, the sender needs much less processi...
Multicast Disadvantages <ul><li>Multicast is UDP-based. </li></ul><ul><li>Best-effort delivery </li></ul><ul><ul><li>Heavy...
Types of Multicast Applications <ul><li>One-to-many </li></ul><ul><li>A single host sending to two or more (n) receivers <...
IP Multicast Applications Corporate Broadcasts Distance Learning Training Videoconferencing Whiteboard/Collaboration Multi...
Self Check <ul><li>List some advantages of multicast transmission over unicast transmission. </li></ul><ul><li>How does th...
Multicast Addressing
IP Multicast Address Structure <ul><li>IP group addresses: </li></ul><ul><li>Class D address (high-order three bits are se...
Multicast Addressing  IPv4 Header Options Padding Time to Live Protocol Header Checksum Identification Flags Fragment Offs...
IP Multicast Address Groups <ul><li>Local scope addresses </li></ul><ul><ul><li>224.0.0.0 to 224.0.0.255 </li></ul></ul><u...
Local Scope Addresses <ul><li>Well-known addresses assigned by IANA </li></ul><ul><li>Reserved use: 224.0.0.0 through 224....
Global Scope Addresses <ul><li>Transient addresses, assigned and reclaimed dynamically (within applications): </li></ul><u...
Administratively Scoped Addresses <ul><li>Transient addresses, assigned and reclaimed dynamically (within applications): <...
Layer 2 Multicast Addressing <ul><li>IEEE 802.3 MAC Address Format </li></ul>
IANA Ethernet MAC Address Range 01-00-5e-00-00-00 through 01-00-5e-7f-ff-ff Available range of MAC addresses for IP multic...
IANA Ethernet MAC Address Range <ul><li>Within this range, these MAC addresses have the first 25 bits in common.  </li></u...
Ethernet MAC Address Mapping
Multicast Addressing 224.1.1.1 224.129.1.1 225.1.1.1 225.129.1.1 . . . 238.1.1.1 238.129.1.1 239.1.1.1 239.129.1.1 0x0100....
Madcap in MS Server
How are Multicast Addresses Assigned?  <ul><li>Static Global Group Address Assignment  </li></ul><ul><li>Temporary method ...
Learning About Multicast Sessions <ul><li>Potential receivers have to learn about multicast streams or sessions available ...
sdr—Session Directory
A Cisco IP/TV Example <ul><li>Cisco IP/TV  a pplication </li></ul><ul><li>Clients ( v iewers) use  p rogram  l isting </li...
Self Check <ul><li>What is the address range for multicast addresses? </li></ul><ul><li>What are Local Scope Addresses? </...
Summary <ul><li>IP multicast is a much more efficient means of delivering content where a single sender needs to deliver t...
Q and A
Resources <ul><li>Wikipedia IP Multicast article </li></ul><ul><ul><li>http://en.wikipedia.org/wiki/IP_Multicast   </li></...
 
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  • Multicast deployments require three elements: the application, the network infrastructure, and client devices. IP Multicast is a bandwidth-conserving technology that reduces traffic by simultaneously delivering a single stream of information to thousands of corporate recipients and homes. IP Multicast utilizes a single data stream, which is replicated by routers at branch points throughout the network. This mechanism uses bandwidth much more efficiently and greatly decreases load on content servers, reaching more users at a lower cost per user. IP Multicast is an efficient means of delivering media to many hosts over a single IP flow.
  • IP Multicast technologies enable scalable distribution of data, voice, and video streams efficiently to hundreds, thousands, even millions of users. Multicast enables corporate communications, financial trading, video conferencing, E-learning, commercial Television and Radio over IP, streaming media applications, and Multicast enabled VPN services. These types of applications have become an effective means of corporate communication; however, sending combined media over a campus data network brings with it the potential for high bandwidth consumption.
  • Most of this information is covered in CCNP 3 v4.0 Module 8: Multicast may be used to send the same data packets to multiple receivers. By sending to multiple receivers the packets are not duplicated for every receiver, but are sent in a single stream where downstream routers take care of packet multiplication over receiving links. Routers process less packets since they receive only a single copy of the packet. This packet is then multiplied and sent on outgoing interfaces where there are receivers. Because downstream routers take care of packet multiplication and delivery to receivers, the sender or source of multicast traffic does not have to know about receivers’ unicast addresses. Simulcast – simultaneous delivery for a group of receivers - can be used for deploying software upgrades or patches. The main points: Reduced load on Server. Reduced load on Network Links Scales to ‘any’ number of receivers
  • This information is covered in CCNP 3 v4.0 Module 8: Unicast transmission sends multiple copies of data, one copy for each receiver: The top example shows a host transmitting 3 copies of data and a network forwards each packet to 3 separate receivers. The host can only send to one receiver at a time since it has to create a different packet destination address for each receiver. Multicast transmission sends a single copy of data to multiple receivers: The lower example shows a host transmitting 1 copy of data and a network replicates the packet at the last possible hop for each receiver, each packet exists only in a single copy on any given network. The host can send to multiple receivers simultaneously since it’s sending only one packet.
  • Multicast transmission affords many advantages over unicast transmission in a one-to-many or many-to-many environment : Enhanced Efficiency: available network bandwidth is utilized more efficiently since multiple streams of data are replaced with a single transmission Optimized Performance: less copies of data require forwarding and processing Distributed Applications: multipoint applications will not be possible as demand and usage grows because unicast transmission will not scale ( traffic level and clients increase at a 1:1 rate with unicast transmission ) Multicast enables a whole range of new applications that were not possible on unicast (for example, video on demand [VoD]).
  • There are also some disadvantages of multicast that need to be considered Most Multicast Applications are UDP based. This results in some undesirable side-effects when compared to similar unicast, TCP applications. Best Effort Delivery results in occasional packet drops. Drops are to be expected. Multicast applications must not expect reliable delivery of data and should be designed accordingly. Many multicast applications that operate in real-time (e.g. Video, Audio) can be impacted by these losses. Also, requesting retransmission of the lost data at the application layer in these sort of real-time applications is not feasible. Reliable multicast applications will address this issue. Heavy drops on Voice applications result in jerky, missed speech patterns that can make the content unintelligible when the drop rate gets high enough. Moderate to Heavy drops in Video is sometimes better tolerated by the human eye and appear as unusual “artifacts” on the picture. However, some compression algorithms can be severely impacted by even low drop rates; causing the picture to become jerky or freeze for several seconds while the decompression algorithm recovers. No Congestion Control can result in overall Network Degradation as the popularity of UDP based Multicast applications grow. The lack of TCP windowing and “slow-start” mechanisms can result in network congestion. If possible, multicast applications should attempt to detect and avoid congestion conditions. Duplicate packets can occasionally be generated as multicast network topologies change. Applications should expect occasional duplicate packets to arrive and should be designed accordingly. Out-of-sequence delivery of packets to the application may also result during network topology changes or other network events that affect the flow of multicast traffic. Efficient filtering and security for multicast flows is a big issue since senders randomly select UDP ports and very often multicast addresses as well. This kind of behavior prevents effective static filtering.
  • There are different types of multicast applications. Two most common models are: one-to-many model where one sender sends data to many receivers Examples of uses of the one-to-many model are: Audio or video distribution Push media Announcements Monitoring If a one-to-many application needs feedback from receivers, then it becomes a many-to-many application. many-to-many model where a host can be a sender as well as receiver simultaneously Examples of uses of the many-to-many model are: Collaboration Concurrent processing Distributed interactive simulations Other models (e.g. many-to-one where many receivers are sending data back to one sender) are used less frequently. Examples of uses of the many-to-one model are: Resource discovery Data collection Auctions Polling
  • Many new multipoint applications are emerging as demand for them grows: Real-time applications include live broadcasts, financial data delivery, whiteboard collaboration, and video conferencing. Non-real-time applications include file transfer, data and file replication, and video-on-demand. Note also that the latest version of Novell Netware uses IP multicast for file and print service announcements.
  • Enhanced Efficiency: available network bandwidth is utilized more efficiently since multiple streams of data are replaced with a single transmission. Optimized Performance: less copies of data require forwarding and processing. Distributed Applications: multipoint applications will not be possible as demand and usage grows because unicast transmission will not scale. Best Effort Delivery results in occasional packet drops. Drops are to be expected. Multicast applications must not expect reliable delivery of data and should be designed accordingly. Many multicast applications that operate in real-time (e.g. Video, Audio) can be impacted by these losses. Also, requesting retransmission of the lost data at the application layer in these sort of real-time applications is not feasible. One-to-many, many-to-many, and many-to-one. Examples of uses of the one-to-many model are: Audio or video distribution, Push media, Announcements, Monitoring. many-to-many model where a host can be a sender as well as receiver simultaneously.
  • This information is covered in CCNP 3 v4.0 Module 8: The Internet Assigned Numbers Authority (IANA) controls the assignment of IP multicast addresses. IANA has assigned the IPv4 Class D address space to be used for IP multicast. Class D addresses are denoted by the high 4 bits set to 1110. Therefore, all IP multicast group addresses fall in the range from 224.0.0.0 through 239.255.255.255. The remaining 28 bits of the IP address identify the multicast group ID. This multicast group ID is a single address typically written as decimal numbers in the range 224.0.0.0 through 239.255.255.255. The high-order bits in the first octet identify this 224-base address.
  • The Class D address is used for the destination IP address of multicast traffic for a specific group. Multicast addresses may be dynamically or statically allocated. Dynamic multicast addressing provides applications with a group address on demand. Dynamic multicast addresses have a specific lifetime and applications must request and use the address as needed. Static addresses are used at all times. As with IP addressing, there is the concept of private address space that may be used for local, organization wide traffic and public or Internet wide multicast addresses. There are also addresses reserved for specific protocols that require well-known addresses. The Internet Assigned Numbers Authority (IANA) manages the assignment of multicast addresses that are called permanent host groups and are similar in concept to well known TCP and UDP port numbers.
  • This information is covered in CCNP 3 v4.0 Module 8: The multicast IP address space is separated into following address groups: Local Scope Addresses are addresses 224.0.0.0 through 224.0.0.255 and are Reserved by IANA for network protocol use. Multicasts in this range are never forwarded off the local network regardless of TTL and usually the TTL is set to 1. Global Scope Addresses are addresses 224.0.1.0 through 238.255.255.255 and are allocated dynamically throughout the Internet Administratively Scoped Addresses are addresses 239.0.0.0 through 239.255.255.255 and are reserved for use inside of private domains. Multicast delivery is enabled by setting up a multicast address on the Content Engine in the form of a multicast cloud configuration to which different devices, configured to receive content from the same channel, can subscribe. The delivering device sends content to the multicast address set up at the Content Engine, from which it becomes available to all subscribed receiving devices.
  • This information is covered in CCNP 3 v4.0 Module 8: Local Scope Addresses are addresses 224.0.0.0 through 224.0.0.255 and are Reserved by IANA for network protocol use. Multicasts in this range are never forwarded off the local network regardless of TTL and usually the TTL is set to 1. Network protocols use these addresses for automatic router discovery and to communicate important routing information. Address 224.0.0.1 identifies the all-hosts group. Every multicast-capable host must join this group. If a ping command is issued using this address, all multicast-capable hosts on the network must answer the ping request. Address 224.0.0.2 identifies the all-routers group. Multicast routers must join that group on all multicast-capable interfaces. Other local multicast addresses are: 224.0.0.4 All Distance Vector Multicast Routing Protocol (DVMRP) routers on a subnet 224.0.0.5 All OSPF Routers on a subnet 224.0.0.6 All OSPF DRs on a subnet 224.0.0.9 All RIPv2 routers on a subnet 224.0.0.10 All EIGRP routers on a subnet 224.0.0.13 All PIMv2 routers on a subnet
  • This information is covered in CCNP 3 v4.0 Module 8: For multicast applications, transient addresses are dynamically assigned and then returned for others to use when no longer needed. Two address types are (1) global scope addresses and (2) administratively scoped addresses. Global scope addresses are addresses 224.0.1.0 through 238.255.255.255, and are allocated dynamically throughout the Internet. For example, the 224.2.X.X range is used in Mbone applications. Mbone stands for Multicast Backbone and is a collection of Internet routers that support IP multicasting. The Mbone is used as a virtual network (multicast channel) on which various public and private audio and video programs are sent. Mbone was originated by the Internet Engineering Task Force (IETF) in an effort to multicast audio and video meetings. Some of these addresses have been registered with IANA, for example IP address 224.0.1.1 has been reserved for Network Time Protocol (NTP). Applications that use multicast addresses in the 224.0.1.2/32, 224.0.1.22/23, and 224.0.2.2/32 ranges have been demonstrated to be vulnerable to exploitation, which has led to serious security problems. Addresses in the 232.0.0.0 to 232.255.255.255 range are reserved for Source Specific Multicast (SSM). SSM is an extension of Protocol Independent Multicast (PIM), which allows for an efficient data delivery mechanism in one-to-many communications. Parts of a global scope are also used for new protocols and temporary usage: 224.1.0.0-224.1.255.255 ST Multicast Groups 224.2.0.0-224.2.127.253 Multimedia Conference Calls 224.2.127.254 SAPv1 Announcements 224.2.127.255 SAPv0 Announcements (deprecated) 224.2.128.0-224.2.255.255 SAP Dynamic Assignments 224.252.0.0-224.255.255.255 DIS transient groups 232.0.0.0-232.255.255.255 VMTP transient groups
  • This information is covered in CCNP 3 v4.0 Module 8: For multicast applications, transient addresses are dynamically assigned and then returned for others to use when no longer needed. Two address types are (1) global scope addresses and (2) administratively scoped addresses. Like private IP address space that is used within the boundaries of a single organization, &amp;quot;limited&amp;quot; or &amp;quot;administratively scoped&amp;quot; addresses in the range 239.0.0.0 to 239.255.255.255 are constrained to a local group or organization. Companies, universities, or other organizations can use limited scope addresses to have local multicast applications that will not be forwarded over the Internet. Typically, routers are configured with filters to prevent multicast traffic in this address range from flowing outside of an AS. Within an autonomous system or domain, the limited scope address range can be further subdivided so that local multicast boundaries can be defined. This subdivision is called &amp;quot;address scoping&amp;quot; and allows for address reuse between smaller domains. These addresses are described in RFC 2365, Administratively Scoped IP Multicast . Administratively scoped multicast address space is divided into following scopes: Site-local scope (239.255.0.0/16 and grows downward to 239.254.0.0/16, 239.253.0.0/16...) Organization-local scope (239.192.0.0/14 with possible expansion to ranges 239.0.0.0/10, 239.64.0.0/10 and 239.128.0.0/10)
  • Historically, network interface cards (NICs) on a LAN segment could receive only packets destined for their burned-in MAC address or the broadcast MAC address. In IP multicast, several hosts need to be able to receive a single data stream with a common destination MAC address. Some means had to be devised so that multiple hosts could receive the same packet and still be able to differentiate between several multicast groups. One method to accomplish this is to map IP multicast Class D addresses directly to a MAC address. Today, using this method, NICs can receive packets destined to many different MAC addresses—their own unicast, broadcast, and a range of multicast addresses. The IEEE LAN specifications made provisions for the transmission of broadcast and multicast packets. In the 802.3 standard, bit 0 of the first octet is used to indicate a broadcast or multicast frame. The graphic in this slide shows the location of the broadcast or multicast bit in an Ethernet frame. This bit indicates that the frame is destined for a group of hosts or all hosts on the network (in the case of the broadcast address 0xFFFF.FFFF.FFFF). IP multicast makes use of this capability by sending IP packets to a group of hosts on a LAN segment.
  • IANA owns a block of Ethernet MAC addresses that start with 01:00:5E in hexadecimal format. Half of this block is allocated for multicast addresses. The range from 0100.5e00.0000 through 0100.5e7f.ffff is the available range of Ethernet MAC addresses for IP multicast.
  • Within this range, these MAC addresses have the first 25 bits in common. The remaining 23 bits are available for mapping to the lower 23 bits of the IP multicast group address. This allocation allows for 23 bits in the Ethernet address to correspond to the IP multicast group address. The mapping places the lower 23 bits of the IP multicast group address into these available 23 bits in the Ethernet address.
  • Given that the IPv4 Class D Addresses are used for IP multicast, all IP multicast addresses begin with the same first four bits of 1110. Therefore, all IP multicast group addresses fall in the range from 224.0.0.0 through 239.255.255.255. ------------- The remaining 28 bits of the IP address identify the multicast group ID. ------------- When mapping Layer 3 to Layer 2 addresses, the low order 23 bits of the Layer 3 IP multicast address are mapped into the low order 23 bits of the IEEE MAC address. ------------- Notice that this results in 5 bits of information being lost. Because there are 28 bits of unique address space for an IP multicast address (32 bits minus the first 4 bits containing the 1110 Class D prefix), and there are only 23 bits mapped into the IEEE MAC address, there are five bits of overlap, or 28 bits – 23 bits = 5 bits, and 2 to the fifth = 32. Therefore, there is a 32-to-1 overlap of Layer 3 addresses to Layer 2 addresses. Be aware that 32 Layer 3 addresses map to the same Layer 2 multicast address. ------------- Continuing with this example, take the lower 23 bits of the Layer 3 address and convert the binary to hexadecimal. ------------- Then add the prefix of 01:00:5E. ------------- The resulting Layer 2 multicast address of 01:00:5E:01:01:01 will map to the IP multicast address of 224.129.1.1. A bit of History It turns out that this loss of 5 bits worth of information was not originally intended. When Dr. Steve Deering was doing his seminal research on IP Multicast, he approached his advisor with the need for 16 OUI’s to map all 28 bits worth of Layer 3 IP Multicast address into unique Layer 2 MAC addresses. Note: An OUI (Organizationally Unique Identifier) is the high 24 bits of a MAC address that is assigned to “an organization” by the IEEE. A single OUI therefore provides 24 bits worth of unique MAC addresses to the organization. Unfortunately, at that time the IEEE charged $1000 for each OUI assigned which meant that Dr. Deering was requesting that his advisor spend $16,000 so he could continue his research. Due to budget constraints, the advisor agreed to purchase a single OUI for Dr. Deering. However, the advisor also chose to reserve half of the MAC addresses in this OUI for other graduate research projects and granted Dr. Deering the other half. This resulted in Dr. Deering having only 23 bits worth of MAC address space with which to map 28 bits of IP Multicast addresses. (It’s too bad that it wasn’t known back then how popular IP Multicast would become. If they had, Dr. Deering might have been able to “pass the hat” around to interested parties and collected enough money to purchase all 16 OUI’s. :-) )
  • Remember, there is a 32-to-1 overlap of Layer 3 addresses to Layer 2 addresses. Be aware that 32 Layer 3 addresses map to the same Layer 2 multicast address. For example, all of the above IP Multicast addresses map to the same Layer 2 multicast of 01-00-5e-01-01-01.
  • Multicast Address Dynamic Client Allocation Protocol (MADCAP) allows a client workstation to “lease” a multicast address from a MADCAP server in a manner similar to how it “leases” an IP address from a DHCP server. When a MADCAP client workstation wants to “lease” a multicast address, first it must locate the nearest MADCAP Servers. This is accomplished by multicasting a MADCAP DISCOVER message to the MADCAP Scope Relative multicast address (-1) in the Site-Local scope, (for instance, 239.255.255.254). (Note: This is why it is important to adhere to the conventions for the Site-Local scope defined in RFC 2365.) Any MADCAP Servers that hear this Scope Relative multicast message and wish to participate in the allocation process identify themselves by sending back an OFFER message to the MADCAP client. After the client has discovered the appropriate MADCAP server, it can send REQUEST messages to the server to request the “lease” of a multicast address from the server. MADCAP supports the concept of Administratively Scoped Zones. Workstations can request a list of known scope ranges by sending a GETINFO message to one or more MADCAP servers, which respond by sending back a list of its configured multicast scope ranges. This allows the MADCAP client to select the scope range that is most appropriate to the application and subsequently request an address from this range in a REQUEST message. Notice that Microsoft has chosen to include the MADCAP configuration functions inside the DHCP Service even though MADCAP is a separate protocol. This is probably because the concepts of configuring a MADCAP Multicast Scope are like the configuration of a DHCP scope. However, other operating system implementations of MADCAP may take a different approach.
  • Multicast GLOP (a word, not an acronym) addresses in the range 233.0.0.0 to 233.255.255.255 can be used statically by organizations that have an Autonomous System (AS) number is registered by a network registry and listed in the RWhois database. The second and third octets of the domain multicast address are represented by the AS number. For example, AS 62010 is written in hexadecimal format as &amp;quot;F23A.&amp;quot; This value is separated into two parts, F2 and 3A and those numbers, converted to decimal would be 242 and 58. This would yield a multicast GLOP address of 233.242.58.0/24. Multicast group addresses in that address space can be used by the organization with AS 62010 and routed throughout the Internet Multicast Backbone.
  • Whenever a multicast application is started on a receiver the application has to know to which multicast group to join. The application has to learn about the available sessions or streams, which typically map to one ore more IP multicast groups. There are several possibilities for applications to learn about the sessions: The application may join a well-known predefined group to which announcements about available sessions are done. Some type of directory services are available and the application contacts the appropriate directory server. The application can be launched from a web page on which the sessions are listed as URLs; even e-mail can be used. The application can act as a guide, displaying multicast content that has been learned through Session Announcement Protocol (SAP).
  • The Session Directory (sd) application acts as a guide, displaying multicast content. A client application runs on a PC and lets the user know what content is available. This directory application uses either Session Description Protocol (SDP) or Session Announcement Protocol (SAP) to learn about the content. (Note that both the sd application and SDP are sometimes called “SDR” or “sdr” and that in Cisco documentation, SDP/SAP is referred to as “sdr.”) The original sd application served as a means to announce available sessions and to assist in creating new sessions. The initial sd tool was revised, resulting in the Session Description Protocol tool (referred to in this course as “SDR”), which is an applications tool that allows the following: Session description and its announcement Transport of session announcement via well-known multicast groups (224.2.127.254) Creation of new sessions At the receiver side, SDR is used to learn about available groups or sessions. If a user clicks an icon describing a multicast stream listed via SDR, a join to that multicast group is initiated. When SDR is used at the sender side, it is used to create new sessions and to avoid address conflicts. Senders at the time of session creation consult their respective SDR caches (senders are also receivers) and choose one of the unused multicast addresses. When the session is created, the senders start announcing it—with all the information that is needed by receivers to successfully join the session. RFC 3266, which defines SDP, defines the standard set of variables that describe the sessions. Most of those variables were inherited from the SDR tool. The transport itself is not defined in this RFC. The packets describing the session may be transported across the multicast-enabled network via several mechanisms: SAP, defined in RFC 2974, carries the session information. Session Initiation Protocol (SIP), which is defined in RFC 2543, is a signaling protocol for Internet conferencing, telephony, presence, events notification, and instant messaging. Real Time Streaming Protocol (RTSP), which is defined in RFC 2326, serves mainly as a control protocol in a multimedia environment. RTSP allows videocassette recorder (VCR)-like controls (select, forward, rewind, pause, stop, and so on) and also carries information on a session. E-mail (in Multipurpose Internet Mail Extensions [MIME] format) may also carry SDR packets describing the session. Web pages may provide session descriptions in standardized SDR format also. The window on the left shows an example of the SDR application in action. Each line is a multimedia session that has been created by some user in the network and is being announced (via multicast) by the creator’s SDR application. By clicking on one of these sessions, the window on the right is brought up. This window displays various information about the multimedia session including: General session information Session schedule Media type (in this case audio and video) Media format Multicast group and port numbers Using the window on the right, one can have SDR launch the appropriate multicast application(s) to join the session.
  • The SDR mechanisms are shown in this Cisco IP/TV example. Cisco IP/TV generally has three components: Server (the source) Content Manager (the “directory server”) Viewer (the receiver) The Viewers can either: Contact the Content Manager directly (by unicast) and request the list of available programs (sessions, streams) from it Listen to periodic SAP announcements Cisco IP/TV uses SAP to transport the SDR sessions to the viewer. The standard SDR format for session description is used.
  • IANA has assigned the IPv4 Class D address space to be used for IP multicast. Class D addresses are denoted by the high 4 bits set to 1110. Therefore, all IP multicast group addresses fall in the range from 224.0.0.0 through 239.255.255.255. Local Scope Addresses are addresses 224.0.0.0 through 224.0.0.255 and are Reserved by IANA for network protocol use. Multicasts in this range are never forwarded off the local network regardless of TTL and usually the TTL is set to 1. Mbone stands for Multicast Backbone and is a collection of Internet routers that support IP multicasting. The Mbone is used as a virtual network (multicast channel) on which various public and private audio and video programs are sent. Mbone was originated by the Internet Engineering Task Force (IETF) in an effort to multicast audio and video meetings. Remember, there is a 32-to-1 overlap of Layer 3 addresses to Layer 2 addresses. Be aware that 32 Layer 3 addresses map to the same Layer 2 multicast address. Multicast Address Dynamic Client Allocation Protocol (MADCAP) allows a client workstation to “lease” a multicast address from a MADCAP server in a manner similar to how it “leases” an IP address from a DHCP server.
  • 1

    1. 1. BSCI Module 7 Lesson 1 IP Multicasting: Explaining Multicast
    2. 2. Objectives <ul><li>Describe the IP multicast group. </li></ul><ul><li>Compare and contrast Unicast packets and multicast packets. </li></ul><ul><li>List the advantages and disadvantages of multicast traffic. </li></ul><ul><li>Discuss two types of multicast applications. </li></ul><ul><li>Describe the types of IP multicast addresses. </li></ul><ul><li>Describe how receivers can learn about a scheduled multicast session. </li></ul>
    3. 3. Multicast Overview
    4. 4. IP Multicast Distribute information to large audiences over an IP network
    5. 5. Multicast Adoption Past, Present, and Future Multicast (1986-2005) 1992 1996 1997 1998 2000 2001 2002 2003 2004 2005 1986 Time Multicast Deployment Early Adopters NASA, DOD, Cisco, Microsoft, Sprint Financials NASDAQ, NYSE, LIFE, Morgan, GS, Prudential E Learning 150 Universities in US, Hawaii, Oregon, USC, UCLA, Berkley Corporate Communication HP, IBM, Intel, Ford, BMW, Dupont MXU & Content Providers Fastweb, B2, Yahoo, BBC, CNN z z z Research Community MBONE Surveillance Law Enforcement and Federal IPv6 Multicast NTT, Sony, Panasonic, Multicast VPN C&W, MCI, AT&T, TI, FT, DT, NTT
    6. 6. Why Multicast? <ul><li>Used when sending same data to multiple receivers </li></ul><ul><li>Better bandwidth utilization </li></ul><ul><li>Less host/router processing </li></ul><ul><li>Used when addresses of receivers unknown </li></ul><ul><li>Used when simultaneous delivery for a group of receivers is required (simulcast) </li></ul>
    7. 7. Unicast vs. Multicast
    8. 8. Multicast Advantages <ul><li>Enhanced efficiency : Controls network traffic and reduces server and CPU loads </li></ul><ul><li>Optimized performance : Eliminates traffic redundancy </li></ul><ul><li>Distributed applications : Makes multipoint applications possible </li></ul>
    9. 9. Other Multicast Advantages <ul><ul><li>For the equivalent amount of multicast traffic, the sender needs much less processing power and bandwidth. </li></ul></ul><ul><ul><li>Multicast packets do not impose as high a rate of bandwidth utilization as unicast packets, so there is a greater possibility that they will arrive almost simultaneously at the receivers. </li></ul></ul>
    10. 10. Multicast Disadvantages <ul><li>Multicast is UDP-based. </li></ul><ul><li>Best-effort delivery </li></ul><ul><ul><li>Heavy drops in Voice traffic </li></ul></ul><ul><ul><li>Moderate to Heavy drops in Video </li></ul></ul><ul><li>No congestion avoidance </li></ul><ul><li>Duplicate packets may be generated </li></ul><ul><li>Out - of - sequence delivery may occur </li></ul><ul><li>Efficiency issues in filtering and in security </li></ul>
    11. 11. Types of Multicast Applications <ul><li>One-to-many </li></ul><ul><li>A single host sending to two or more (n) receivers </li></ul><ul><li>Many-to-many </li></ul><ul><li>Any number of hosts sending to the same multicast group; hosts are also members of the group (sender = receiver) </li></ul><ul><li>Many-to-one </li></ul><ul><li>Any number of receivers sending data back to a source (via unicast or multicast) </li></ul>
    12. 12. IP Multicast Applications Corporate Broadcasts Distance Learning Training Videoconferencing Whiteboard/Collaboration Multicast File Transfer Data and File Replication Real-Time Data Delivery—Financial Video-on-Demand Live TV and Radio Broadcast to the Desktop
    13. 13. Self Check <ul><li>List some advantages of multicast transmission over unicast transmission. </li></ul><ul><li>How does the best effort delivery nature of UDP impact multicast transmissions? </li></ul><ul><li>What are the 3 basic types of multicast applications? </li></ul><ul><li>Give examples of one-to-many. </li></ul><ul><li>What model is used when a host can be a sender as well as a receiver simultaneously? </li></ul>
    14. 14. Multicast Addressing
    15. 15. IP Multicast Address Structure <ul><li>IP group addresses: </li></ul><ul><li>Class D address (high-order three bits are set) </li></ul><ul><li>Range from 224.0.0.0 through 239.255.255.255 </li></ul>
    16. 16. Multicast Addressing IPv4 Header Options Padding Time to Live Protocol Header Checksum Identification Flags Fragment Offset Version IHL Type of Service Total Length Source Address Destination Address Destination Source Source Address can never be Class D Multicast Group Address 224.0.0.0 - 239.255.255.255 (Class D) Multicast Group Address Range Destination 1.0.0.0 - 223.255.255.255 (Class A, B, C) Source
    17. 17. IP Multicast Address Groups <ul><li>Local scope addresses </li></ul><ul><ul><li>224.0.0.0 to 224.0.0.255 </li></ul></ul><ul><li>Global scope addresses </li></ul><ul><ul><li>224.0.1.0 to 238.255.255.255 </li></ul></ul><ul><li>Administratively scoped addresses </li></ul><ul><ul><li>239.0.0.0 to 239.255.255.255 </li></ul></ul>
    18. 18. Local Scope Addresses <ul><li>Well-known addresses assigned by IANA </li></ul><ul><li>Reserved use: 224.0.0.0 through 224.0.0.255 </li></ul><ul><ul><ul><li>224.0.0.1 (all multicast systems on subnet) </li></ul></ul></ul><ul><ul><ul><li>224.0.0.2 (all routers on subnet) </li></ul></ul></ul><ul><ul><ul><li>224.0.0.4 (all DVMRP routers) </li></ul></ul></ul><ul><ul><ul><li>224.0.0.13 (all PIMv2 routers) </li></ul></ul></ul><ul><ul><ul><li>224.0.0.5, 224.0.0.6, 224.0.0.9, and 224.0.0.10 used by unicast routing protocols </li></ul></ul></ul>
    19. 19. Global Scope Addresses <ul><li>Transient addresses, assigned and reclaimed dynamically (within applications): </li></ul><ul><ul><li>Global range: 224.0.1.0-238.255.255.255 </li></ul></ul><ul><ul><li>224.2.X.X usually used in MBONE applications </li></ul></ul><ul><li>Part of a global scope recently used for new protocols and temporary usage </li></ul>
    20. 20. Administratively Scoped Addresses <ul><li>Transient addresses, assigned and reclaimed dynamically (within applications): </li></ul><ul><li>Limited (local) scope: 239.0.0.0/8 for private IP multicast addresses (RFC-2365) </li></ul><ul><ul><ul><li>Site-local scope: 239.255.0.0/16 </li></ul></ul></ul><ul><ul><ul><li>Organization-local scope: 239.192.0.0 to 239.251.255.255 </li></ul></ul></ul>
    21. 21. Layer 2 Multicast Addressing <ul><li>IEEE 802.3 MAC Address Format </li></ul>
    22. 22. IANA Ethernet MAC Address Range 01-00-5e-00-00-00 through 01-00-5e-7f-ff-ff Available range of MAC addresses for IP multicast
    23. 23. IANA Ethernet MAC Address Range <ul><li>Within this range, these MAC addresses have the first 25 bits in common. </li></ul><ul><li>The remaining 23 bits are available for mapping to the lower 23 bits of the IP multicast group address. </li></ul>00000001:00000000:01011110:00000000:00000000:00000000 through Available range of MAC addresses for IP multicast 00000001:00000000:01011110:01111111:11111111:11111111
    24. 24. Ethernet MAC Address Mapping
    25. 25. Multicast Addressing 224.1.1.1 224.129.1.1 225.1.1.1 225.129.1.1 . . . 238.1.1.1 238.129.1.1 239.1.1.1 239.129.1.1 0x0100.5E01.0101 1 - Multicast MAC Address (FDDI and Ethernet) 32 - IP Multicast Addresses Be Aware of the 32:1 Address Overlap IP Multicast MAC Address Mapping (FDDI & Ethernet)
    26. 26. Madcap in MS Server
    27. 27. How are Multicast Addresses Assigned? <ul><li>Static Global Group Address Assignment </li></ul><ul><li>Temporary method to meet immediate needs </li></ul><ul><li>Group range: 233.0.0.0 – 233.255.255.255 </li></ul><ul><ul><li>Your AS number is inserted in middle two octets </li></ul></ul><ul><ul><li>Remaining low-order octet used for group assignment </li></ul></ul><ul><li>Defined in RFC 2770 </li></ul><ul><ul><li>“GLOP Addressing in 233/8” </li></ul></ul><ul><li>Manual address allocation by the admin is still the most common practice. </li></ul>
    28. 28. Learning About Multicast Sessions <ul><li>Potential receivers have to learn about multicast streams or sessions available before a multicast application is launched. </li></ul><ul><li>Possibilities: </li></ul><ul><li>Another multicast application sending to a well-known group whose members are all potential receivers </li></ul><ul><li>Directory services </li></ul><ul><li>Web page, e-mail </li></ul><ul><li>Session Announcement Protocol (SAP) </li></ul>
    29. 29. sdr—Session Directory
    30. 30. A Cisco IP/TV Example <ul><li>Cisco IP/TV a pplication </li></ul><ul><li>Clients ( v iewers) use p rogram l isting </li></ul><ul><ul><li>Contact the server directly </li></ul></ul><ul><ul><li>Listen to SAP announcements </li></ul></ul>
    31. 31. Self Check <ul><li>What is the address range for multicast addresses? </li></ul><ul><li>What are Local Scope Addresses? </li></ul><ul><li>What is Mbone? </li></ul><ul><li>What is the 32-to-1 overlap? </li></ul><ul><li>What is MADCAP? </li></ul>
    32. 32. Summary <ul><li>IP multicast is a much more efficient means of delivering content where a single sender needs to deliver the content to multiple receivers. This task may be achieved through the use of multicast groups. </li></ul><ul><li>IP multicasts are designated by the use of a specific Class D IP address range. This is achieved through global scope addresses, which are assigned dynamically, and administratively scoped, which are assigned locally and are reserved for use inside private domains. </li></ul>
    33. 33. Q and A
    34. 34. Resources <ul><li>Wikipedia IP Multicast article </li></ul><ul><ul><li>http://en.wikipedia.org/wiki/IP_Multicast </li></ul></ul><ul><li>Webopedia Mbone article </li></ul><ul><ul><li>http://www.webopedia.com/TERM/M/Mbone.html </li></ul></ul>

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