public ip over private lease line

Question

I have a private cross-connection with a service provider

This private connection is connected from my firewall to their router and the L3 IP range /30 for this segment is private

However, i just realized that when they provided us their application IP to connected to over this connection is a public IP

The source IP i am using is actually still a private IP but yet the destination i am connecting to is a public IP and this is done over a private cross-connect with a private /30 transit network

Can a public IP transverse a private network ? I mean this cross-connection is not facing the internet - how does it work ?

Thank you

Answer 1

An IP address is an IP address. Public and Private are artificial labels. What makes an address "private" is a loose agreement that no one will route it over the public internet. However, within one's own network, one may do whatever they wish. While it's a bad practice to mix private and public traffic, there's nothing logically wrong with it. "192.168.1.1" can talk to anything that knows how to get back to it; the internet at large won't have a route, but inside an ISP's network, anything goes.

(This may work because the ISP is internally translating your "private" network. I've seen this done a few times, and it can be very confusing if you don't know about all the address translations. If it's not your mess to manage, take it at face value that it works.)