Routing protocols are divided into the following three classes, depending on how they work:

  1. Distance Vector – Distance Vector protocols are characterized by two things:
    • They use distance has a measure of the cost of a route. The number of hops in between a router and a destination network determines the distance.
    • They periodically send their entire routing table to the neighboring routers. The receiving router then merges its routing table with the received information based on AD and metrics. This process is called routing by rumor since the receiving router believes the information received from the neighbor.
    • Distance vector protocols are slower to converge. A network is considered converged when all routers in the network know about all destination networksDistance Vector protocols are relatively easier to configure, manage and    troubleshoot. However on the other hand, they consume a lot more bandwidth and CPU because they periodically send out the entire routing table, irrespective of the fact that nothing has changed in between the period. RIP is an example of a distance vector protocol.
  2. Link State – Link state protocols are characterized by the following three things:
    • They form a neighbor relation with other routers before sharing the routing information. They do not send out routing information to the entire network as in case of distance vector protocols. Information related to their neighbors are stored in a table.
    • They only exchange connectivity related information or link states, unlike distance vector protocols that send out routing tables. This information is stored n a topology table to construct a full view of the network.
    • Based on links states received, each router calculates the best path to every destination in the network. Each protocol has its own algorithm to calculate the best path.
    • Link state updates are sent out only when there is a change instead of periodically as in case of distance vector protocols.
    • Link state protocols converge faster than distance vector protocols.Link State Protocols are a little more complex to configure, manage and troubleshoot compared to distance vector protocols.  OSPF is an example of a link state protocol.

3.  Hybrid – Hybrid protocols use aspects of both distance vector and link state protocols. EIGRP is an example of hybrid protocol.

Exam Alert: Differences between the different classes as well as example of each class is an important topic in the CCNA exam.