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© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicBSCI Module 7 Lesson 1 1

BSCI Module 7 Lesson 1

IP Multicasting: Explaining Multicast


Objectives

Describe the IP multicast group.

Compare and contrast Unicast packets and multicast packets.

List the advantages and disadvantages of multicast traffic.

Discuss two types of multicast applications.

Describe the types of IP multicast addresses.

Describe how receivers can learn about a scheduled multicast session.


Multicast Overview


IP Multicast

Distribute information to large audiences over an IP network


Multicast AdoptionPast, Present, and Future

Multicast (1986-2005)Multicast (1986-2005)

1992 1996 1997 1998 2000 2001 2002 2003 2004 20051986Time

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

Multicast D

eployment

Multicast D

eployment

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


Why Multicast?

Used when sending same data to multiple receivers

Better bandwidth utilization

Less host/router processing

Used when addresses of receivers unknown

Used when simultaneous delivery for a group of receivers is required (simulcast)


Unicast vs. Multicast


Multicast AdvantagesEnhanced efficiency: Controls network traffic and reduces server and CPU loads

Optimized performance: Eliminates traffic redundancy

Distributed applications: Makes multipoint applications possible


Other Multicast Advantages For the equivalent amount of multicast traffic, the

sender needs much less processing power and bandwidth.

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.


Multicast Disadvantages

Multicast is UDP-based.

Best-effort deliveryHeavy drops in Voice traffic

Moderate to Heavy drops in Video

No congestion avoidance

Duplicate packets may be generated

Out-of-sequence delivery may occur

Efficiency issues in filtering and in security


Types of Multicast Applications

One-to-many

A single host sending to two or more (n) receivers

Many-to-many

Any number of hosts sending to the same multicast group; hosts are also members of the group (sender = receiver)

Many-to-one

Any number of receivers sending data back to a source (via unicast or multicast)


Corporate Broadcasts

Distance Learning

Training

Videoconferencing

Whiteboard/Collaboration

Multicast File TransferData and File Replication

Real-Time Data Delivery—FinancialVideo-on-Demand

Live TV and Radio Broadcast to the Desktop

IP Multicast Applications


Self Check

1. List some advantages of multicast transmission over unicast transmission.

2. How does the best effort delivery nature of UDP impact multicast transmissions?

3. What are the 3 basic types of multicast applications?

4. Give examples of one-to-many.

5. What model is used when a host can be a sender as well as a receiver simultaneously?


Multicast Addressing


IP Multicast Address Structure

IP group addresses:

Class D address (high-order three bits are set)

Range from 224.0.0.0 through 239.255.255.255



IPv4 Header

Options Padding

Time to Live Protocol Header Checksum

Identification Flags Fragment Offset

Version IHL Type of Service Total Length

Source Address

Destination AddressDestination

Source

Source Address can never be

Source Address can never be

Class D Multicast Group Address

Class D Multicast Group Address

224.0.0.0 - 239.255.255.255 (Class D) Multicast Group Address RangeDestination

1.0.0.0 - 223.255.255.255 (Class A, B, C)Source


IP Multicast Address Groups

Local scope addresses224.0.0.0 to 224.0.0.255

Global scope addresses224.0.1.0 to 238.255.255.255

Administratively scoped addresses239.0.0.0 to 239.255.255.255


Local Scope Addresses

Well-known addresses assigned by IANA

Reserved use: 224.0.0.0 through 224.0.0.255224.0.0.1 (all multicast systems on subnet)

224.0.0.2 (all routers on subnet)

224.0.0.4 (all DVMRP routers)

224.0.0.13 (all PIMv2 routers)

224.0.0.5, 224.0.0.6, 224.0.0.9, and 224.0.0.10 used by unicast routing protocols


Global Scope Addresses

Transient addresses, assigned and reclaimed dynamically (within applications):

Global range: 224.0.1.0-238.255.255.255

224.2.X.X usually used in MBONE applications

Part of a global scope recently used for new protocols and temporary usage


Administratively Scoped Addresses

Transient addresses, assigned and reclaimed dynamically (within applications):

Limited (local) scope: 239.0.0.0/8 for private IP multicast addresses (RFC-2365)

Site-local scope: 239.255.0.0/16

Organization-local scope: 239.192.0.0 to 239.251.255.255


Layer 2 Multicast Addressing

IEEE 802.3 MAC Address Format


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


00000001:00000000:01011110:00000000:00000000:00000000

IANA Ethernet MAC Address Range

through

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.

Available range of MAC addresses for IP multicast

00000001:00000000:01011110:01111111:11111111:11111111


Ethernet MAC Address Mapping


224.1.1.1224.129.1.1225.1.1.1225.129.1.1 . . .238.1.1.1238.129.1.1239.1.1.1239.129.1.1

0x0100.5E01.0101

1 - Multicast MAC Address(FDDI and Ethernet)

32 - IP Multicast Addresses


Be Aware of the 32:1 Address OverlapBe Aware of the 32:1 Address Overlap

IP Multicast MAC Address Mapping(FDDI & Ethernet)


Madcap in MS Server


How are Multicast Addresses Assigned?

Static Global Group Address Assignment

Temporary method to meet immediate needs

Group range: 233.0.0.0 – 233.255.255.255Your AS number is inserted in middle two octets

Remaining low-order octet used for group assignment

Defined in RFC 2770“GLOP Addressing in 233/8”

Manual address allocation by the admin is still the most common practice.


Learning About Multicast Sessions

Potential receivers have to learn about multicast streams or sessions available before a multicast application is launched.

Possibilities:

Another multicast application sending to a well-known group whose members are all potential receivers

Directory services

Web page, e-mail

Session Announcement Protocol (SAP)


sdr—Session Directory


A Cisco IP/TV Example

Cisco IP/TV application

Clients (viewers) use program listingContact the server directly

Listen to SAP announcements


Self Check

1. What is the address range for multicast addresses?

2. What are Local Scope Addresses?

3. What is Mbone?

4. What is the 32-to-1 overlap?

5. What is MADCAP?


Summary

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.

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.


Q and A


Resources

Wikipedia IP Multicast articlehttp://en.wikipedia.org/wiki/IP_Multicast

Webopedia Mbone articlehttp://www.webopedia.com/TERM/M/Mbone.html

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Technology

multicast packets

multicast advantages

future multicast

multicast systems

multicast overview

ip multicast group address

multicast group hosts

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