Fundamentals of Multicast

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Multicast is UDP Based!!! Best Effort Delivery: Drops are to be expected. Multicast applications should not expect reliable delivery of data and should be designed accordingly. Reliable Multicast is still an area for much research. Expect to see more developments in this area. No Congestion Avoidance: Lack of TCP windowing and “flow-control” mechanisms can result in network congestion. If possible, Multicast applications should attempt to detect and avoid congestion conditions. Duplicates: Some multicast protocol mechanisms (e.g. Asserts, Registers and Shortest-Path Tree Transitions) result in the occasional generation of duplicate packets. Multicast applications should be designed...

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Nội dung Text: Fundamentals of Multicast

Fundamentals of Multicast Fundamentals of Multicast BSCI © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 1
CCNP – BSCI Bachkhoa Networking Academy Objectives – Why Multicast – Multicast Applications – Multicast Service Model – Multicast Distribution Tree om – Multicast Forwarding .c – Multicast Protocol Basics a d 5 .0 ac v – Multicast Protocol Review . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 2
CCNP – BSCI Bachkhoa Networking Academy Why Multicast?  When sending same data to multiple receivers  Better bandwidth utilization  Less host/router processing  Receivers’ addresses unknown om .c a d 5 .0 ac v . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 3
CCNP – BSCI Bachkhoa Networking Academy Unicast vs Multicast om .c a d 5 .0 ac v . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 4
CCNP – BSCI Bachkhoa Networking Academy Multicast Advantages  Enhanced Efficiency: Controls network traffic and reduces server and CPU loads  Optimized Performance: Eliminates traffic redundancy  Distributed Applications: Makes multipoint applications possible om .c a d 5 .0 ac v . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 5
CCNP – BSCI Bachkhoa Networking Academy Multicast Disadvantages Multicast is UDP Based!!!  Best Effort Delivery: Drops are to be expected. Multicast applications should not expect reliable delivery of data and should be designed accordingly. Reliable Multicast is still an area for much research. Expect to see more developments in this area.  No Congestion Avoidance: Lack of TCP windowing and “flow- control” mechanisms can result in network congestion. If om possible, Multicast applications should attempt to detect and avoid congestion conditions. .c d ca v5.0  Duplicates: Some multicast protocol mechanisms (e.g. Asserts, kaapplications Registers and Shortest-Path Tree Transitions) result in the occasional generation of duplicate packets. Multicast P b N .packets. w C should be designed to expect occasional duplicate w C w  Out-of-Sequence Packets: Various network events can result in packets arriving out of sequence. Multicast applications should be designed to handle packets that arrive in some other sequence than they were sent by the source. BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 6
CCNP – BSCI Bachkhoa Networking Academy IP Multicast Applications om .c a d 5 .0 ac v . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 7
CCNP – BSCI Bachkhoa Networking Academy IP Multicast Service Model  RFC 1112 (Host Ext. for Multicast Support)  Each multicast group identified by a class-D IP address  Members of the group could be present anywhere in the Internet  Members join and leave the group and indicate this to the routers m co  Senders and receivers are distinct: d . .0 ca v5 ka P –i.e., a sender need not be a member .b N  Routers listen to all multicast addresses and use multicast routing protocols to manage ww CC groups w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 8
CCNP – BSCI Bachkhoa Networking Academy IP Multicast Service Model  IP Addresses use the Class D address space –Class D addresses are denoted by the high 4 bits set to 1110.  Local Scope Addresses –Addresses 224.0.0.0 through 224.0.0.255 –Reserved by IANA for network protocol use •224.0.0.1 All Hosts 224.0.0.2 All Multicast Routers m co •224.0.0.3 All DVMRP Routers 224.0.0.5 All OSPF Routers •224.0.0.6 All OSPF DR d . .0 ca v5 ka P  Global Scope Addresses –Addresses 224.0.1.0 through 238.255.255.255 .b N –Allocated dynamically throughout the Internet w C w C  Administratively Scoped Addresses w –Addresses 239.0.0.0 through 239.255.255.255 –Reserved for use inside of private Domains BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 9
CCNP – BSCI Bachkhoa Networking Academy Multicast Protocol Basics  Multicast Distribution Trees  Multicast Forwarding  Types of Multicast Protocols –Dense Mode Protocols –Sparse Mode Protocols om .c a d 5 .0 ac v . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 10
CCNP – BSCI Bachkhoa Networking Academy Multicast Distribution Trees om .c a d 5 .0 ac v . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 11
CCNP – BSCI Bachkhoa Networking Academy Multicast Distribution Trees om .c a d 5 .0 ac v . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 12
CCNP – BSCI Bachkhoa Networking Academy Multicast Distribution Trees om .c a d 5 .0 ac v . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 13
CCNP – BSCI Bachkhoa Networking Academy Multicast Distribution Trees om .c a d 5 .0 ac v . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 14
CCNP – BSCI Bachkhoa Networking Academy Multicast Distribution Trees om .c a d 5 .0 ac v . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 15
CCNP – BSCI Bachkhoa Networking Academy Multicast Distribution Trees Characteristics of Distribution Trees  Source or Shortest Path trees –Uses more memory O(S x G) but you get optimal paths from source to all receivers; minimizes delay  Shared trees –Uses less memory O(G) but you may get sub-optimal paths from source to all receivers; may introduce extra delay m co d . .0 ca v5 ka P .b N w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 16
CCNP – BSCI Bachkhoa Networking Academy Multicast Distribution Trees How are Distribution Trees Built?  PIM –Uses existing Unicast Routing Table plus Join/Prune/Graft mechanism to build tree.  DVMRP –Uses DVMRP Routing Table plus special Poison-Reverse mechanism to build tree m co d . .0  MOSPF ca v5 – Uses extension to OSPF’slink state mechanism to build tree. ka P .b N  CBT –Uses existing Unicast Routing Table plus w C Join/Prune/Graft w C mechanism to build tree. w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 17
CCNP – BSCI Bachkhoa Networking Academy Multicast Forwarding  Multicast Routing is backwards from Unicast Routing –Unicast Routing is concerned about where the packet is going. –Multicast Routing is concerned about where the packet came from. m co  Multicast Routing uses “Reverse Path Forwarding” d . .0 ca v5 ka P .b N w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 18
CCNP – BSCI Bachkhoa Networking Academy Reverse Path Forwarding (RPF)  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 routing table used for multicasting is checked against the om “source” address in the multicast datagram. .c –If the datagram arrived on the interface specified in the routing a d 5 .0 table for the source address; then the RPF check succeeds. –Otherwise, the RPF Check fails. ac v . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 19
CCNP – BSCI Bachkhoa Networking Academy Reverse Path Forwarding (RPF)  If the RPF check succeeds, the datagram is forwarded  If the RPF check fails, the datagram is typically silently discarded  When a datagram is forwarded, it is sent out each interface in the outgoing interface list  Packet is never never forwarded back out the RPF m interface! . co a d 5 .0 ac v . bk NP w C w C w BSCI © 2008 Cisco Systems, Inc. All rights reserved. Học viện mạng Bách Khoa - www.bkacad.com 20