Routing

Routing

1. Distance Vector

   • Routing by rumour
     • Routing information is only recieved from immediate neighbours.
     • The information gained from each router then updates the routing table and enables each router to have an understanding of the network
     • The information that has been passed from each neighbouring router, is then passed to the other neighbouring routers.
   • 1) Each router informs its neighbour of its directly connected network
     • 2) Includes networks the router has learned from other neighbours
       • 3) Share the metrics (Cost) of the routes it knows
         • 4) In DV protocols the metrics is distance initially hop count (how many routers the packet has to cross to reach its distance) i.e. 3 hops = metric of 3
   • Negatives
     • Hop count and bandwidth does improve the efficiency of the routing, one problem is the consumation of network resources full routing tables. Meaning broadcasts can occur every 30 seconds
     • Routing tables can be extremely large
     • Can also increase the convergence due to delay incurred in sending so many packet updates

2. Link State

   • Shortest path first
     • Disregars the idea of rouing by rumour, works on first hand knowledge
     • improvements over DV
       • Updated packets sent via multicast not broadcast
       • Reduces unnecessary traffic
       • Configured in a heirarchical fashion
   • Linked state advertisement
     • LSA is the process of how data is transmitted, it includes the state of the directly connected router links
     • Link state determines the amount of routers, as well as the networks which are connected to them
       • Each router can then create a topology of the network
     • Convergence is improved as only the link state is sent and not the whole routing table
   • Metric is based on bandwidth
     • To populate the routing table, it runs the shortest path first alogrithm
     • Less prone to loops as each router has a map of the system

3. DV vs. LS

   • DV = needs to be told distance by another router
   • LS = calculates the distance to another network