Routing Table

A routing  table has columns  for at  three types o information  the network  ID  the cost  and the  ID of the  next  router. The  network  ID is the final  destination of the packet. The cost  is  the number of hops  a packets  must make  to get  there. And  the next  router is the router  to which  a packet  must  be delivered  on its  way  to a particular destination.

The  original  routing  tables for  our sample  internetwork  are show  in this point  the third  column is empty because the only  destination network  identified  are those  attached to the current  router.

No multiple  hop  destination and  therefore  no next  router have been identified. These  basic  tables  are sent out to neighbours. For  example A sends is  routing take  to routers B, F sends E, B send it routing table  to routers C and A  and so on:

When a receives  a routing  from  B it uses the information to update  its own  table. A adjusts  the information  shown B table by  adding  one to  each listed cost. It then  combines  the table  with it own to create a new  more comprehensive  table.

This  process  continues for all routers. Every  router  receives information from  neighbours  and updates its  routing  table. If  there are no more  changes the final  tables  may look like  those shown.