Distance Vector Routing Explained

The Problem Routing Algorithms Solve

A router needs to decide which direction to forward a packet toward its final destination, often with many possible paths through the network. Routing algorithms are the rules routers use to build and maintain a map of the best paths available.

The Core Idea Behind Distance Vector

Each router keeps a simple table: for every destination network it knows about, how far away is it (usually measured in "hops," the number of routers to cross), and which neighbor should it send traffic to in order to get there.

Router A's table:
Destination     Distance    Next Hop
Network 1       0 hops      (directly connected)
Network 2       1 hop       Router B
Network 3       2 hops      Router B

"Routing by Rumor": Learning Only from Neighbors

Each router periodically shares its entire table with its directly connected neighbors. A router never sees the whole network's true shape - it only trusts what its neighbors tell it, then updates its own table if a neighbor claims a shorter path exists. This is why distance vector routing is sometimes called "routing by rumor."

The Slow Convergence Problem

Because routers only exchange information with immediate neighbors, it can take several rounds of updates for a change (like a failed link) to propagate across the whole network - during which routers may temporarily have outdated or even incorrect information, sometimes causing routing loops until everything settles.

Where This Approach Is Used

RIP (covered in its own note in this section) is the classic real-world example of a distance vector protocol - simple to understand and configure, but generally reserved for smaller networks due to its slower convergence compared to link state routing.