Introduction to Routing in IP: Intradomain & Interdomain

Introduction

If every router on the Internet had to manage routing entries for the entire Internet, then we would need very high-end and high performing routers. Also, the scale of exchanging routing information would be humongous. Instead, the Internet consists of separate administrative domains. Each domain is run and managed by an independent authority.

The Internet is hence comprised of domains. A domain can be a small enterprise that manages a few routers in a single building, a larger enterprise with a hundred routers at multiple locations, or a large Internet Service Provider managing thousands of routers. For example, Verizon is responsible for managing all devices in its networks.

As of this writing, the Internet is composed of more than $30,000$ such different domains and this number is still growing.