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# Routing basics

## on Oct 06, 2011

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Seminar on IP Routing protocols with simulations using Cisco Packet Tracer.

Seminar on IP Routing protocols with simulations using Cisco Packet Tracer.

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## Routing basicsPresentation Transcript

• ROUTING PROTOCOLS Narendran Thangarajan, @naren_live SSN College of Engineering, Chennai.
• RECAP..  MAIN CLASSIFICATION  STATIC ROUTING  DYNAMIC ROUTING  Concept of Autonomous System (AS)  What is dynamic in Dynamic Routing Protocols?
• RECAP – Dynamic Routing Protocols  Dynamic Routing Classification  IntraDomain  Distance Vector  Link State  InterDomain  Path Vector
• RECAP – Distance Vector Routing Distance Vectors shared Initialization – directly connected routers Sharing – Share the first two columns of the routing table Updating – Better cost replaces old entry When to share? – Periodic and triggered Problems Eg: RIP
• LINK STATE ROUTING Goal : To find the shortest path to the destination. Difference from DV : In DV each router knows only the next hop. But in LS each router has the entire topology of the domain.
• Steps: Initial State : All routers know their own link state. Creation of LSPs Reliable Flooding of LSPs Formation of Shortest Path Tree Routing Table Calculation
• Creating LSP Link State Packets (LSP) carry large amount of information. Also called Hello Packets. Important Fields : Router ID, Link state of the router, Sequence number, Time to Live. Created on two occasions:  When there is change in the topology.  Periodic basis.
• Reliable Flooding ALL nodes broadcast their LSPs to their adjacent nodes. Depending upon the sequence number and the link state values, the receiving node decides whether to discard or store the LSP.
• Formation of Shortest Path tree  After the LSP are shared among all nodes, each and every node has the entire topology of the domain.  Then Dijkstra’s algorithm is run over this information to create a shortest path tree from the graph obtained.  Permanent List and Tentative list – An eg. Problem  Demo - http://www.ifors.ms.unimelb.edu.au/tutorial/dijkstra /island.html
• Creation of routing table From the generated shortest paths, the routing table is generated. In both DV and LS, the final routing table is the same. The difference lies only in the way the routing table is prepared.
• OSPF – Open Shortest Path First  The Autonomous System is divided into Areas.  LS routing protocol runs inside an Area.  The summary of the routing information is given to the Backbone area through ABR.
• Simulations
• Thank you 