My purpose is to make a P2P software.Firstly I make some test.
After I connect to web via pppoe, I visit different website’s phpinfo() page, but the result of _SERVER[“REMOTE_PORT”] is different.
Including some ip address lookup site like http://www.whatismyip.com, http://www.apnic.net etc. and gmail’s ip location lookup list are all different. Why?
Is these different ip address allocated by ISP on different web resources ? Is the private routing to different web resources changed?
Maybe the reason is CDN by my ISP or the website? If the reason is the ip address allocated by ISP on different web resources, the website visitor’s ip address may unreal.
My ISP has little ip address,so I am under a NAT.Even if under a NAT,the public ip address shouldn’t change with different web resources.
But I can use some p2p software ,why? If the ip address change with visiting different web resources, the NAT traversal of P2P software may be very difficult.
If you do not have a static IP with your ISP, you can expect that “your” public outgoing IP changes as you access different ressources on Internet; your ISP is likely using a wide range of public IPs for outbound connections and you end up on one of them depending on how their internal routing works.
Your P2P software works, because it never receives inbound connections: it establishes (synchronous->HTTP or full duplex->websockets, etc…..) outbound connections to a central server or a relay and receives data inbound on the return channel.