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IP Multicasting

Background knowledge, What is IP Multicasting

Applications and Architecture

IGMP

Multicast routing

Reverse Path Forwarding (RPF)

Multicast distribution

PIM and Mapping and Rendezvous point

Address translation

IP Multicasting

“Implementation of multicast communication in internet”

Individual hosts are configured as members of different multicast groups

One particular user may a member of many multicast groups

For a one multicast can be few members/nodes

IP Multicast group is identified by Class D address (224.0.0.0 –

239.255.255.255)

Every IP datagram send to a multicast group is transferred to all members

of group

Applications Situations where multiple end points need to receive identical info at same

time

News/Sports/Stocks/Weather updates

Teleconferencing (Audio, Video, White board etc…)

Distance learning

Data replication

Stream video

Issues

Complexity

Early days routers are not configured to do multicasting in proper

manner

IP Multicasting components IP multicast addressing (how we address

IP Group management

Multicast routing

Multicasting is UDP based

Best effort delivery

No congestion avoidance

Added complexity

IP Multicasting considerations

Multicast Fundamentals

IP Multicast protocol stack

Multicast Address translation In Ethernet Mac addresses a multicast address is identified by setting the

lowest bit of the most left byte

First 4 bytes -> Class D address

Special Class D addresses

224.0.0.1 really means all systems on this subnet

224.0.0.2 means all routers on this subnet

224.0.1.1 is for NTP (Network Time Protocol) used for synchronizing

machines

224.0.0.9 is for RIP-2 (a routing protocol).

Internet Group Management Protocol (IGMP)

Use by host to notify the local router that it wishes to receive (or stop

receiving) multicast traffic for given destination node or group

IGMP operates on physical network

Eg: single Ethernet segment

IGMP supports

Joining a multicast group

Query membership

Send membership reports

IGMP snooping

Send multicast only to needed ports

Multicast Routing Source can determine who can be the member of group and who will not

be

Required mechanism

Packet forwarding can send multiple copies of same packet

Multicast routing algorithm which builds spanning tree

Two types of trees

Source Tree

Shared Tree

Single copy replicate in network

Routing tables are different in the two trees

Protocol Independent Multicast (PIM)

Router to router signal protocol

Use by a router to notify an upstream router that it wishes to receive (or

stop receiving) multicast traffic

Three main classifications of PIM

Dense

Sparse

Sparse dense

Source specific

Bidirectional

Reverse Path Forwarding (RPF)

PIM-SM Rendezvous Point (RP)

PIM-SM uses a router called Rendezvous Point

The purpose of RP to allow, the first hop router to find out the IP address of

the source for a particular group.

The receiver don’t know the source address

A RP is mandatory for PIM Sparse Mode

PIM-SM Rendezvous Point Discovery

Static RP configuration

Dynamic RP configuration

Multicast advantages

Enhanced scalability

Network utilization is independent of the number of receivers

Network handle replication

Reduce resource utilization

Controls network bandwidth and reduces server and router load

Deterministic performance

Subscriber number 1 and subscriber number 10000 have identical

experience

Summery IP Multicasting is somewhat similar to “spreading of virus”

Replication at each router

Functions are layered

IGMP to handle host to router

PIM to inter router signaling

Different message formats for IP Multicasting

Scalability accommodate more functions and features

References

[1] YouTube. “Lecture - 32 IP Multicasting”. Youtube.com. [Online]. Available

https://www.youtube.com/watch?v=TApIo_BiX6U [Accessed: 3 Aug2014].

[2] YouTube. “Cisco Live 2014: IP Multicast Concepts, Design and Troubleshooting

(Melbourne)”. Youtube.com. [Online]. Available https://www.youtube.com/watch?v=l9RJdrdjDU8

[Accessed: 3 Aug2014].