it's being said that a peer to peer network is not server-based for routing and processing data and only uses server for getting the up to dated nodes addresses (probably their internet IP address) to connect to other node directly without no intermediate server. so my question is, how computer(node) A can establish a connection with node B over the internet. the IPs that ISP gives to us is invalid and isn't reachable. so how does this p2p work with these invalid node IP address over internet?

  • Unfortunately, questions about home networking, consumer-grade devices, and protocols above OSI layer-4, e.g. Skype, are off-topic here. You could try to ask this question on Super User. – Ron Maupin Apr 20 '19 at 21:34

the IPs that ISP gives to us is invalid and isn't reachable.

That can't be true. When the public IP address is invalid you can't do anything with the connection.

Many P2P networks use a directory server like you seem to describe to find each other. Often, destination NAT/reverse NAT/port forwarding is additionally required to connect to hosts behind a router using source NAT (assuming IPv4 is used).

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  • well,so, it's being said that skype uses p2p connection. i use skype and i have not configured my modem/router for NAT and Port Forwarding. so how the connection is established? – Mehrdad Dadvand Apr 20 '19 at 20:46
  • Skype isn’t a true p2p network. See this paper for more details www1.cs.columbia.edu/~salman/publications/skype1_4.pdf – Ron Trunk Apr 20 '19 at 20:57
  • i just run ping [my internet public ip] from another computer but no replay and even i setup port forwarding on my modem to route to my pc with nc.exe and telnet. but no connection was established. i think my ISP don't allow all incoming connection to direct to my modem. it just route those request that already requested from my pc. can it be true? – Mehrdad Dadvand Apr 20 '19 at 21:05
  • ping uses ICMP echo requests and you can't port forward those since ICMP doesn't use ports. Note that not all consumer-grade routers support port forwarding/DNAT and consumer-grade hardware is off-topic here. – Zac67 Apr 20 '19 at 21:36
  • i know ICMP don't use port but i expected my modem it self reply to icmp packet. not only icmp, i even setup a tcp port forward to forward to my pc and i test it by telnet my public ip from other systen which was connected to the internet. the connection didn't established.it's too weird. – Mehrdad Dadvand Apr 21 '19 at 5:14

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