What is the use of private ASNs?

Question

I am currently studying BGP at the moment.

The public ASNs that are assigned to ISPs and larger organizations that want to participate in routing on the internet make perfect sense to me.

However, I've heard that there are also private AS numbers that can be used? What exactly is the real-world use of these? Are these used for internal BPG? I haven't managed to find a sufficient explanation online.

Thank you for your help in advance.

Answer 1

Private ASNs exist for the same purpose as private IP addresses - if you peer in a private area but still want to use BGP then you don't require public ASNs. Use cases include private peering points, inter-organization exchanges or links.