Leased lines - addressing scheme/how they work

Hi all, I'm a little confused as to how leased lines work especially the addressing scheme used i.e. public or private IP addressing. For instance what kind of IP (private or public) will the router connecting to the POP in the diagram here: tinyurl.com/6zp87r use?

I personally think it'll be a private IP since the router looks WAN facing from the diagram and since the provider will provide Internet access but I cant convince myself.

Any clarification will be appreciated.
Thanks


Ps.not the best of sites to look up such things i know... but i just used this site for a reason

The WAN facing interface will be Public, the ISP will need to advertise this linking subnet to the internet else the network won't be reachable by anyone - 'private' addresses aren't routable.

The LAN facing interface will use either private / public addressing depending on the setup with the ISP. If they are using NAT the LAN interface will be private, if the ISP is routing another subnet down the link the LAN interface will have a public address.

I personally think it'll be a private IP since the router looks WAN facing from the diagram and since the provider will provide Internet access but I cant convince myself.

I agree with novembre that the WAN interface of the router has to have a public IP. And to convince your self of that, picture that the same POP might be offering other leased line WAN connections to other customers in the area. If we assume all those WAN links use pirivate IPs, then the provider will have to make sure those private ranges don't overlap (which is an added burden since private IPs are meant to overlap between differing networks). Also the POP will have to share a single public IP for all those customers and do NATing for them (which is very unlikely as far as I've seen).

Hope I'm not out of scope.

Thanks guys...leased line configuration seems to confuse me alot especially when it comes to their addressing maybe because i havent delved into it as much as i should. I understand the diff, meaning, usage of private & public IP's so i see what you mean from your explanation.

I think what confused me was the fact that leased lines are also referred to as Private lines so I thought that'll mean private ips as well...

Thanks guys...leased line configuration seems to confuse me alot especially when it comes to their addressing maybe because i havent delved into it as much as i should.

Just remember that there is nothing special about leased lines at Layer 3 - the picture could be representing other WAN access technologies like ATM / Metro Ethernet / Frame Relay / whatever. The key here is that servers in the LAN want to access and be accessible from the Internet, so they need to have or be represented by a public address.

btw there are ways you can handle private addressing in this scenario, but they obviously aren't being used here. Just using a public address is most common.