IP Routing

Preface

Ants, single-celled creatures such as the cellular slime mold, plants and animals in ecosystems, and (even) human beings can congregate and display miraculously complex behaviors.^[1] Say a colony of ants in a tree needs to move to another tree, perhaps in search of food. Some ants build a bridge by joining their bodies in a chain stretching from one limb in one tree to another limb in another tree. Other ants cross over this ant structure, walking over their peers. Once all the ants have crossed over, the ants in the bridge begin to gracefully undo the structure, crossing one by one. Each ant only repeats simple actions, over and over again; the net result of thousands of ants working together is the miracle of the bridge, which allows the ant colony to migrate.

In our own human society we hope to emulate this level of cooperation. Each one of us is useful to others in some way: we write, lay bricks, act in the theater, farm, drive buses, repair helicopters, tend to the sick, make coffee... As individuals, we repeat the same acts again and again, whether it be making coffee cup after coffee cup or seeing patient after patient. The net result of all these acts is our complex, wonderful society.

So, what does all this have to do with IP routing? Each router in a network repeats simple processes over and over again, as described in the specification of the routing protocol it is executing. The net result of all the routers in a network repeating these simple processes is IP routing, ...