Interior vs Exterior Gateway Protocols

Question

I'm new to Networking and I was reading about the Interior and Exterior Gateway Protocols ,but i couldn't understand some points , as stated in a reference:

IGPs are designed to work in private networks. An IGP is used to route within the individual networks of a single organization (networks having the same autonomous system).

EGPs on the other hand, are designed for use between different autonomous systems that are under the control of different administrations. They can be used to provide paths in the public network (Internet)

The Internet is a network of networks, and autonomous systems are the big networks that make up the Internet. So according to this what i want to know:

• Does a company private network can be considered as an autonomous system ? In other words , How Networks are classified as a single a autonomous system ? having the same routing policy ? IP Ranges ?
• Do interior gateway protocols such RIP, OSPF and EIGRP are only used on private networks and not used on the internet ?
• If so , Does BGP is the only protocol that is used on the internet to connect different autonomous systems?

Also any example would be appreciated .

Regards

Answer 1

In practice, there is only one EGP in use today, and that is BGPv4. OSPF and EIGRP are the most common IGPs. RIP is essentially obsolete.

Can a company private network be considered as an autonomous system ?

The term autonomous system really only makes sense when using the BGP protocol. So if a company is not running BGP, the term has little meaning.

While it's common for a company network to be considered an autonomous system, a company can have many autonomous systems in its network, or many companies can be part of one AS. There is no hard and fast rule

Are interior gateway protocols such RIP, OSPF and EIGRP only used on private networks and not used on the internet ? Is BGP the only protocol that is used on the internet to connect different autonomous systems?

Correct. BGP is the only protocol used between autonomous systems on the Internet.

How are networks classified as a single a autonomous system? Having the same routing policy? IP Ranges?

Again, there is no rule. If you're struggling with the term, it's because there is no rule to follow. The network designer can create one or more autonomous systems depending on the organizations needs. For example, one of my clients has many remote locations, and each one is a separate AS. Some locations have more than one AS. But they're all under the same administrative control.