Difference Between Distance Vector Routing and Link State Routing

Routing is the mechanism of transferring information from a source to destination across an internetwork. The distance vector routing and link state routing are the two of routing algorithms, categorised depending on the way the routing tables are updated.

The prior difference between Distance vector and link state routing is that in distance vector routing the router share the knowledge of the entire autonomous system whereas in link state routing the router share the knowledge of only their neighbour routers in the autonomous system.

Content: Distance Vector Routing Vs Link State Routing

1. 1. Comparison Chart
   2. Definition
   3. Key Differences
   4. Conclusion

Comparison Chart

Basis for comparison	Distance vector routing	Link state routing
Algorithm	Bellman ford	Dijsktra
Network view	Topology information from the neighbour point of view	Complete information on the network topology
Best path calculation	Based on the least number of hops	Based on the cost
Updates	Full routing table	Link state updates
Updates frequency	Periodic updates	Triggered updates
CPU and memory	Low utilisation	Intensive
Simplicity	High simplicity	Requires a trained network administrator
Convergence time	Moderate	Fast
Updates	On broadcast	On multicast
Hierarchical structure	No	Yes
Intermediate Nodes	No	Yes

Definition of Distance Vector Routing

In distance vector routing, a router need not know the entire path to every network segment; it only requires to know the direction or vector in which to send the packet. The technique determines the direction (vector) and distance (hop count) to any network in the internetwork.

Distance vector routing algorithms periodically send all or parts of their routing table to their adjacent neighbours. The routers running a distance vector routing protocol will automatically send periodic updates even if there are no changes in the network.

A router can verify all the known routes and alters its local routing table on the basis of the updated information received from neighbouring routing. This process is referred to as “routing by rumour” because the routing information that a router has of the network topology is based on the perspective of the routing table of the neighbour router.

RIP and IGRP is a commonly used distance vector protocol that uses hop counts or its routing metrics.

Definition of Link State Routing

In link-state routing, each router attempt to construct its own internal map of the network topology. At the initial stage of start-up, when a router becomes active, it sends the messages into the network and collects the information from the routers to which it is directly connected. It also provides information about whether the link to reach the router is active or not. This information is used by other routers to build a map of network topology. Then the router uses the map to choose the best path.

The link state routing protocols respond swiftly to the network changes. It sends triggered updates when a network change occurs and sends periodic updates at long time intervals such as 30 minutes. If the link alters state, the device detected the alteration generates and propagate an update message regarding that link to all routers. Then each router takes a copy of the update message and update its routing table and forwards the message to all neighbouring router.

This flooding of the update message is needed to ensure that all routers update their database before creating an update routing table that reflects the new technology. OSPF protocol is the example link state routing.

Conclusion

In distance vector routing the routing share, the information of the entire autonomous system and the information is shared only with neighbours. On the other hand, in link state routing the routers share the knowledge only about their neighbours and the information is shared with all routers.