The Control Plane: Distance Vector - Routing Information Protocol

Introduction

The Routing Information Protocol (RIP) based on the famous Belmman-Ford algorithm belongs to the distance vector class of routing algorithms and was used in ARPANET. While it used to be incredibly popular, it’s not used very much now. There are other distance vector routing algorithms too such as Ford-Fulkerson.

Initial State

Each router or ‘node,’ maintains a routing table that initially contains the estimated cost to each of its neighbors.

Consider the following example of a small network where the yellow circles represent nodes, the black lines represent links, and the purple numbers represent the cost of each link.

Initial Routing Table #

What would the initial routing table look like at node C for example?

Destination	Cost	Next Hop
A	5	A
B	3	B
D	4	D

initial routing table at C

The table contains:

1. The names of the destination nodes which are the neighbors in this case.
2. The initial cost of the link to each of C’s neighbors,
3. The ‘next hop’ node, i.e. the node that C would have to send a packet to in order for it to reach its destination. In this case, the next hop and the destination are the same since the destinations are all C’s neighbors.

Every node receives all of its neighbors’ routing tables in two cases:

1. When a trigger happens such as a router or link failure happens.
2. Every

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