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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].