Ip multicast
- 2. Agenda What is Multicast ? Why Multicast ? Applications of Multicast Multicast Addresses How Multicast Works ? IGMP overview How IGMP Works ? IGMP v1,v2 and v3 Multicast distribution trees (Source and Shared) PIM-SM,PIM-DM,PIM-SSM Challenges to Multicast Summary
- 3. Definition 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.
- 4. One to Many communication Multiple Unicast Multicast
- 5. Why Multicast Multicast is... a need. Well, at least in some scenarios. If you have information (a lot of information, usually) that should be transmitted to various (but usually not all) hosts over an internet, then Multicast is the answer. One common situation in which it is used is when distributing real time audio and video to the set of hosts which have joined a distributed conference. When sending to multiple receivers: Better bandwidth utilization Fast processing Lower router cycles required
- 6. Multicast applications Any Applications with multiple receivers 1-to-many or many-to-many Live Video distribution Periodic Data Delivery - "Push" technology stock quotes, sports scores, magazines, newspapers Advertisements Server/Web-site replication Reducing Network/Resource Overhead more efficient to establish multicast tree rather then multiple point-to- point links Distributed Interactive Simulation (DIS) wargames virtual reality
- 7. IP Multicast addresses Class D addresses: 224.0.0.0 - 239.255.255.255 Addresses Description Can only be used to specify a “Group”, Source addresses are always unicast ip 224.0.0.1 All hosts in this subnet addresses. 224.0.0.2 All routers in this subnet 224.0.0.0 to 224.0.0.255 – reserved to be used by network protocols locally, it means they are only locally significant and packets destined to these addresses will never get 224.0.0.5 OSPF forwarded by router. 224.0.0.6 OSPF DR 239.0.0.0/8 is currently an administratively scoped address space. 224.0.0.12 DHCP server/Relay agent The 232.0.0.0/8 block is reserved for use by Source-specific multicast (SSM).
- 8. GLOP addresses GLOP addresses Provides globally available private Class D space 233.x.x.y/24 per AS number RFC2770 How? AS number = 16 bits Insert the 16 ASN into the middle two octets of 233/8
- 10. Internet Group Management Protocol (IGMP) Used by the hosts to indicate that they want to join a particular group and used by the routers to discover if there is any intended receiver in the subnet. Flavors of IGMP: IGMP v1 , v2 and v3 { v = version }
- 11. How IGMP works Multicast Router 1. Interested receivers send Membership-Report to nearest multicast router 2. Upon receiving Membership-Report Multicast Router starts sending traffic to that subnet 3. Router periodically send Membership - Query to check if there is any Hosts intended receiver in the subnet. If three consecutive queries fails then IGMP Report router stops sending traffic to that Multicast Traffic subnet. IGMP Query
- 12. IGMP version-1 IGMP version 1 has 2 types of messages: 1. Membership Query: Used by Router to check whether there is any interested receiver for a particular group. 2. Membership Report: Used by the hosts to send their willingness to join a particular group.
- 13. IGMP version-2 IGMP version 2 has 4 types of messages : 1. Membership Query – Same as v1 2. V-1 Membership report – v1 report 3. V-2 Membership report – v2 report 4. Leave group – Used by the hosts to show their intention to leave the group.
- 14. IGMP version-3 IGMP v3 is used for “source filtering” ,it means the host will tell the router which group it wants to receive traffic from and also which source it is looking for. It enables routers to send traffic only from the sources for which traffic has been requested by the receivers. IGMP v3 has 2 options in it : Include: Which source it wants to receive traffic from. Exclude: Which source it doesn’t want to receive traffic from.
- 15. Multicast distribution trees Multicast distribution trees are the mechanisms, which allows a control over “how multicast traffic will flow towards the receivers” There are two types of distribution trees: 1. Source distribution tree 2. Shared distribution tree
- 16. Source distribution tree In source tree the root is at the source. Source S Always most promising path is selected. Hence known as Shortest Path Tree. A B D F Notation: (S,G) S comma G S Source C E S : Source G : Group R Receiver R R Multicast traffic flow
- 17. Characteristic of Source tree Each router has to contain (S,G) entry for all the sources hence memory requirement is high. Surety of best possible path from source to receiver. Best suitable for the topology where receivers are densely segregated throughout the network and senders are less in numbers ( Eg. Radio Broadcast).
- 18. Shared distribution tree In Shared trees there is one focal point (known as Source S1 Rendezvous point , RP) in the middle of network and sources forward traffic towards this and intern the RP forwards that traffic downward to all intended receivers. RP S2 A B D F Notation: (*,G) Star comma G C E * : Any Source G : Group R R
- 19. Characteristic of Shared tree Uses less resources. There is a possibility of sub-optimal paths from source to receiver hence RP should be planned carefully. RP itself and its location may affect the performance. Best suitable for many to many applications
- 20. Reverse Path Forwarding What is RPF? A router forwards a multicast datagram only if received on the up stream interface to the source (i.e. it follows the distribution tree). The RPF Check The source IP address of incoming multicast packets are checked against a unicast routing table. If the datagram arrived on the interface specified in the routing table for the source address; then the RPF check succeeds. Otherwise, the RPF Check fails.
- 21. RPF Checks RPF Check Fails RPF Check Succeeds
- 22. Protocol Independent Multicast PIM is the Multicast routing protocol which is completely independent of underlying IP protocol. Though PIM is multicast protocol but it takes help of existing unicast routing protocol to make RPF check and to perform multicast routing/forwarding function and it doesn’t send or receive multicast routing updates like other routing protocols. PIM Types : 1. PIM-Dense Mode 2. PIM-Sparse Mode 3. PIM-Source Specific Multicast
- 23. PIM-DM PIM-DM uses “Push” model to send multicast data down to receivers. PIM-DM floods multicast data to all the corners of the network and the routers which do not have any downstream receiver prune back the unwanted traffic. This process repeats every 3 minutes. “Flood and prune” is used by the routers to gather multicast information. PIM-DM only supports source trees and can not be used for shared trees. Example: Company-wide announcement
- 24. PIM-DM Contd… Receiver Source Traffic is being forwarded to every corner of the IGMPv2 host report Network. Pruned interface Source tree Receiver
- 25. PIM-SM PIM-SM uses “Pull” model to send multicast data down to receivers. Traffic will be forwarded to those receivers who explicitly request for a particular group. PIM-SM uses shared trees to forward multicast data. Initially only shared tree will be created and depending upon the configuration options, traffic can remain in shared tree or can switch to optimal source tree. PIM-SM uses the concept of RP. Example: Space shuttle launch
- 26. PIM-SM join RP Source Receiver announces desire to join group G with igmpv2 host report – (*,G). IGMPv2 host report (*, G) State created from the (*, G) Join RP to the receiver. Shared tree Receiver
- 27. PIM-SM sender registration RP Source (S, G) State created only Shared Tree along the Source Tree. Traffic Flow (S, G) Register (unicast) (S, G) Join Receiver Source Tree
- 28. PIM-SM traffic flow RP Source Source traffic flows natively Traffic Flow along SPT to RP. Shared Tree From RP, traffic flows down Source Tree the Shared Tree to Receivers. Receiver
- 29. PIM-SSM No shared trees No register packets No RP mapping required (no RP required!) No RP-to-RP source discovery (MSDP) Requires IGMP include-source list – IGMPv3 User-definable range IANA specifies 232/8 for global SSM
- 30. PIM-SSM join RP Source Receiver announces desire to join group G AND source S with an IGMPv3 include-list. Last-hop router joins the Source (S, G) Join Tree. Source Tree (S,G) state is built between the Traffic Flow source and the receiver. Receiver
- 31. PIM-SSM traffic flow RP Source Data flows down the source tree to the receiver. Source Tree Traffic Flow Receiver
- 32. Key challenges in Multicast How can a sender restrict who can receive? need authentication, authorization encryption of data key distribution still an active area of research
- 33. The Soup IGMP : Internet Group Management Protocol is used by hosts and routers to tell each other about group membership. PIM-SM : Protocol Independent Multicast-Sparse Mode is used to propagate forwarding state between routers. SSM : Source Specific Multicast utilizes a subset of PIM’s functionality to guaranty source-only trees in the 232/8 range. RP : An RP acts as the meeting place for sources and receivers of multicast data. In a PIM-SM network, sources must send their traffic to the RP. This traffic is then forwarded to receivers down a shared distribution tree