Distance Vector Routing Protocols definition

Distance Vector means ‘distance to final destination’ and ‘Vector, or direction, traffic should be directed’. 

In Distance vector protocol router only knows its neighbour, but it does not know where that neighbor learned the route. Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP) and Enhanced Interior Gateway Routing Protocol (EIGRP) are famous distance vector protocols.

The main Characteristics of Distance Vector routing protocols are

        i.            Periodic updates

      ii.            Neighbors

    iii.            First time use Broadcast updates, send updates on 255.255.255.255 (Entire routing table is included with routing update)

In distance vector routing routers do not have knowledge of the entire path to a destination, just knows it’s connect neighbor. 

Advantages of distance vector protocol:

        i.            Distance vector protocol are simple to implement normally you don’t need much expertise to implement this.

      ii.            Usually Distance vector routing protocols don’t required costly and hardware with high performance.    

Disadvantages of distance vector protocol:

        i.            Distance vector protocols have slow convergence as compare to link state routing protocols.

      ii.            Normally distance vector protocols are suitable for small networks.

    iii.            Most distance vector routing protocols take the very simple approach of telling their neighbors everything they know by broadcasting their entire route table.

     iv.            Routing loops can occur in distance vector protocols because of slow convergence, although there are some methods that are used for avoiding loop in these protocols.

How distance vector routing protocols works:

        i.            In network discovery process every router adds its connected network to its routing tables. And send the information about the connected networks to its neighbours. For example in below figure R0 send the info about its connect networks to 11.0.0.0, 11.1.0.0, 11.2.0.0 and 192.168.0.0 to R1 and vice versa in case of R1.

      ii.            Routers will exchange routing information and routing updates received from other routers

    iii.            If there is new information then Metric is updated new information is stored in routing table

     iv.            Once the process is completed all routing tables in the network contain the same network information. You can see in figure that each router have all networks in its routing table.

Routing loops can be occur in distance vector (need modifications)

Routing loops are a condition in which packets continuously traverse a network. Routing loop effects networks performance by use of bandwidth and extra CPU usage. You can minimize routing loops by defining maximum hop count, hold-down timers, split horizon, route poisoning and triggered updates.

• Causes of routing loops

–        Incorrectly configured static routes

–        Incorrectly configured route redistribution

–        Slow convergence

–        Incorrectly configured discard routes

Examples of Distance Vector Routing Protocols

·         
      RIP (Routing Information Protocol)

RIP is one of famous DV routing protocol. RIP sending out periodic updates. Using 4 different timers to RIP ensure information is accurate and convergence is achieved in a timely manner

·        EIGRP (Enhanced Interior Gateway Routing Protocol)

A distance vector routing protocols that has some features of link state routing protocols

EIGRP is a Cisco proprietary routing protocol. EIGRP sending out triggered updates