1 / 28

S7C9 - Multicasts

S7C9 - Multicasts. Characteristics Management Configuration. Traffic Types. Unicast Single copy to every client unicast address Concern is number of user connections & replication Eat up bandwidth Includes replication at router and across links Suitable for small numbers of destinations

jadon
Download Presentation

S7C9 - Multicasts

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. S7C9 - Multicasts Characteristics Management Configuration

  2. Traffic Types • Unicast • Single copy to every client unicast address • Concern is number of user connections & replication • Eat up bandwidth • Includes replication at router and across links • Suitable for small numbers of destinations • NOTE: IP TV is a streaming video server capable of both unicast and multicast

  3. Broadcast • One copy of each packet to broadcast address • Multimedia broadcasts and be as high as 7 Mbps or more of data • Rarely implemented with multimedia transmissions

  4. Multicast • Packet sent to special multicast address • Single data stream to multiple clients • Saves bandwidth and controls network traffic • Reduces network and host processing

  5. Multicast Traffic Characteristics • Facilitates transmission of an IP datagram to a multicast group identified by single address • Delivers multicast datagram to all members of the multicast group with best effort delivery • Supports dynamic membership of a multicast group • Supports all multicast groups regardless of location or number of members • Supports membership of single host in one or more groups • Upholds multiple data streams at application level for single group address • Supports single group address for multiple applications on host

  6. Multicast Address StructureDestination address only • 224.0.0.0 to 239.255.255.255 • 224.0.0.1 all hosts group • 224.0.0.2 all routers • 224.0.0.4 all distance vector multicast routing protocol • 224.0.0.5 OSPF routers • 224.0.0.6 OSPF designated routers • 224.0.0.9 RIP2 routers • 224.0.0.13 PIM (Protocol Independent Multicast) routers

  7. Multimedia Traffic Issues • Coordinating multicast operations of different devices in the network • Establishing a path between source and destination devices forwarding multicast traffic through the network • Traffic transmitted via a distribution tree • Tree connects all hosts in group • Different protocols use different techniques to construct trees • Routers need to know which hosts belong to group

  8. Subscribing and MaintainingGroups • Issues in facilitating multimedia traffic • Coordinating multicast operations of different devices • Establishing a path between source and destination devices • Forwarding multicast traffic through the network • IGMP provides a means to control and limit the flow of multicast traffic through network • Query messages discover which network devices are members of multicast group • Report messages respond to query messages

  9. IGMP v1 • Basic protocol designed to facilitate a device when joining a multicast group • Responsible for communications between host and router • Determines which hosts can join • Decides when host no longer needs to be part of group • Datagram has version number, type, unused, checksum, and group address fields • Addressed to 224.0.0.1 with TTL=1 • Type identifies query or report status • Membership report can be sent without receipt of query • Queries can be sent in rapid succession on startup

  10. IGMP v2 • Router can transmit to selected group • Four types of messages (not 2) • Membership query • Version 2 membership report • Leave report • Version 1 membership report • Frame format is type, response time, checksum, and group address • Router builds table detailed interfaces with one or more hosts in a group

  11. IGMP v2 Querier Election • Elects multicast querier for each network segment • Multicast router with lowest IP address on LAN segment is elected • All routers initially act as querier; when they receive a query message with a lower number, they stop sending query messages

  12. Maintaining a Group • Queries go to 224.0.0.1 group address • Only one member responds; others suppress • General query sets delay times – random times • Responding host sets delay timer – random values • Leaving a group • Host transmits a leave message 224.0.0.2 • Pruning takes place when there is no response to group-specific query

  13. Multicast Traffic in the Switch • Multicast traffic delivered to all ports of a layer 2 switch • Switches must be capable of forwarding to a large number of members without overloading the switch fabric • Switches need some degree of multicast awareness • VLANs can be defined to correspond to multicast group boundaries • Layer 2 switches can snoop IGMP queries and reports to learn port mappings of multicast group members

  14. CGMP • Cisco developed protocol • Enables switch to learn about existence of multicast clients from Cisco routers and layer 3 switches • Based on client/server model; router is server and switch is client • Router creates a CGMP packet; sent to address to which all switches listen; switch creates proper entry in switching table

  15. Multicast Routing • Routers interact with each other to exchange information about neighboring routers • Designated router constructs a tree to connect all members of IP multicast group • Specifies a unique forwarding path between source’s subnet and each subnet containing multicast group members • Only one loop-free path between pairs of routers • Must be dynamically updated • Two types of trees- - source specific and shared distribution

  16. Source Specific Tree • Requires finding shortest path from sends to each receiver • Builds a spanning tree for each potential source of subnetwork • Use a technique called Reverse Path Forwarding (RPF) • Multicast packet interface is called parent link • RPF algorithm reduces unnecessary packet duplication

  17. Shared Distribution Tree • Use distribution centers and construct single multicast tree • Low-overhead and higher end-to-end delay • Single delivery tree shared by all group members • Devices wanting to receive traffic must explicitly join the shared delivery tree • Multicast traffic sent over same tree regardless of source • Can involve single router or group of routers

  18. Treshhold • TTL field controls packet live time • TTL in multicasting uses threshhold concept • Each interface is assigned threshold value • Packets with greater TTL than threshhold are forwarded • Router compares TTL and decrements by 1 before sending out interface

  19. Threshhold Scopes • Default value is 255 – different routing protocols look for different TTL • 0 restricted to same host • 1 restricted to same subnet • 15 restricted to same site • 63 restricted to same region • 127 worldwide • 191 worldwide; limited bandwidth • 255 unrestricted in scope; global

  20. Multicast Routing Protocols • Responsible for constructing multicast delivery trees and forwarding packets • Dense Mode Routing Protocols • Assume almost all routers need to distribute • DVMRP • MOSPF (RFC 1584) – single routing domain • Not supported by Cisco routers • PIM DM • Floods and then prunes • Distance Vector Multicast Routing Protocol • DVMRP (RFC 1075) used on Internet Backbone (Mbone) – uses reverse flooding

  21. PIM Dense Mode • Useful when • Senders and receivers are in close proximity • Few senders and many receivers • Volume of multicast traffic is high • Stream of multicast traffic is constant

  22. Sparse Mode Routing Protocols • Multicast members are sparsely distributed • CBT (Core-based trees) – RFC 2201 • Single tree shared by all members of group • Core router constructs tree • PIM SM ( Protocol-independent Multicast Sparse Mode) • Used when few receivers in a group • Used when traffic is intermittent

  23. IP Multicasting Requirements • IP protocol stack that supports multicasting (RFC 1112( • Servers and clients need applications • NICS on receiving hosts must be configured to monitor multicast packets • High performance backbone with layer 2 and 3 switching • Switches that can handle multicasting

  24. Cisco Software Supports • PIM • IGMP • CGMP • DVMRP

  25. Basic Configuration Tasks • Enable IP multicast routing • Enable PIM on interfaces • Configure rendezvous port • Configure TTL threshhold • Join a multicast group • Change IGMP version • Enable CGMP

  26. Configuration Commands • Ip multicast-routing • Ip pim [dense-mode|sparse-mode|dense-sparse-mode] • Show ip pim interface s0 • Shows next hop IP address, int type, PIM mode, PIM neighbor count, query frequency, IP address of designated router • Show IP pim neighbor e2 • Shows neighbor address, neighbor int, uptime, expire time, mode, and DR

  27. Outgoing List Member Requirements • PIM neighbor was heard on interface • Host serviced by interface has joined a group • Interface manually configured to join a group

  28. Command List

More Related