The shortage of IPv4 addresses is responsible for many issues and trouble in IP deployments today. Real world issues described in this section show the hidden costs of the lack of IPv4 addresses and the lack of functionalities in IPv4 for the current and future use of IP networking.
Skype [Skype] is a Peer-to-Peer (P2P) Voice over IP(VoIP) application and network. The Skype designers claim to traverse any NAT or firewalls to achieve P2P. Since the Skype protocol is not publicly disclosed, researchers have analyzed the protocol and described the process to traverse NAT and firewalls [Baset and Schulzrinne, 2004].
In a nutshell, a Skype client knows in advance some Skype gateways, named supernodes, and discovers others that help (the client) to find its external IPv4 address. The authors of the analysis think this technique is similar to STUN [RFC3489] and TURN [Rosenberg, 2004], discussed more in Section 1.3.1. The client tries to connect to the gateways using UDP; if unsuccessful, it tries TCP; if unsuccessful, it then tries TCP on the HTTP port (80); and if unsuccessful, it tries TCP on the HTTPS port (443). Since HTTP ports are usually opened for outgoing connections in most organization networks, Skype uses these ports as a last resort to traverse the firewall. When this last resort does not work, Skype loops again twice more and if still not successful, finally gives up.
In most cases, the voice traffic between the two ...