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# Routing basics

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

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### Routing basics

1. 1. ROUTING PROTOCOLS Narendran Thangarajan, @naren_live SSN College of Engineering, Chennai.
2. 2. RECAP..  MAIN CLASSIFICATION  STATIC ROUTING  DYNAMIC ROUTING  Concept of Autonomous System (AS)  What is dynamic in Dynamic Routing Protocols?
3. 3. RECAP – Dynamic Routing Protocols  Dynamic Routing Classification  IntraDomain  Distance Vector  Link State  InterDomain  Path Vector
4. 4. 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
5. 5. 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.
6. 6. 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
7. 7. 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.
8. 8. 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.
9. 9. 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
10. 10. 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.
11. 11. 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.
12. 12. Simulations
13. 13. Thank you 