Routing basics

Routing basics

• 1.
  ROUTING PROTOCOLS Narendran Thangarajan, @naren_live SSN College of Engineering, Chennai.
• 2.
  RECAP..  MAINCLASSIFICATION  STATIC ROUTING  DYNAMIC ROUTING  Concept of Autonomous System (AS)  What is dynamic in Dynamic Routing Protocols?
• 3.
  RECAP – DynamicRouting Protocols  Dynamic Routing Classification  IntraDomain  Distance Vector  Link State  InterDomain  Path Vector
• 4.
  RECAP – DistanceVector 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.
  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.
  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.
  Creating LSP  LinkState 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.
  Reliable Flooding  ALLnodes 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.
  Formation of ShortestPath 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.
  Creation of routingtable  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.
  OSPF – OpenShortest 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.
  Simulations
• 13.
  Thank you 