ROUTING ALGORITHM

FLOODING: (STATIC ALGO)

  • An incoming plot on one line is flooded on all other lines.
  • A large no. of duplicate packet may be generated in this way.
  • To control this duplication, a no. of  methods may be used.

HOP-COUNT:

  • Plot is discarded when count reaches Zero.
  • A list of forwarded plot may be maintained & pkts flooded only once.

ADV:

  • Simplicity.
  • A high probability of packets being delivered.
  • Utilizes every path, Hence also uses shortest path.

DISAD:

  • Wastes a lot of bandwidth.
  • Looping of pkts.
  •  
  • Static algo. Current b/w traffic & topology not taken into account.

APPLICATIONS:

  • Distributed databases, military applications.

Image

DISTANCE VECTOR ROUTING:

  • Also called Bellman-ford algo.
  • Each router maintains a distance table.
  • The Null table contains a list of neighbour for a router say R, as well as the cost/distance to reach the neighbours.
  • This knowledge is shared with all the neighbours & the neighbouring route is update their distance table accordingly.
  • In this way, all routers discover the optional distance & the best total cost.
  • Originally used in ARPA net, later replaced by link state & routing algorithm.
  • Examples: RIPV1, RIPV2, IGRP.

LIMITATIONS:

  • Bellman ford algo does not prevent routing loops.
  • Suffers from Count-to-Infinity Problem.

EXAMPLE:

Image

DISTANCE VECTOR (contd):

  • Routing info is only shared with immediate neighbours.
  • A router can’t see beyond its neighbours so this aspect of distance-vector alog is called Routing by Rumour.

 

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