From time to time I decide to check my connections through the netstat command to make sure that everything is in order. In the latest survey surprised to see hundreds of connections from various IP on port 29866. I then decided to check what the program was receiving so many connections, was Skype.
With a little search on Google found that computers using Skype and it has no incoming connections blocked by firewall and / or NAT can act as supernodes (supernodes) and route connections from other users.
Such connections do not transmit voice, only signaling, and help Skype in the task of making a call two users who are firewalled, for example. Traffic is relatively small, no maximum 40 kbps in both directions. The impact on memory and processor is reasonable, almost 60 megs my Skype is taking the memory at this time, and the load on the CPU gets easier to 5%.
In my case I'm on a router with NAT and firewall, but it allows opening doors and so Skype is connected without restrictions. My router is overloaded with so many requests and the web interface just isn't working anymore (anything that does not also happen to use bittorrent or Emule), other routers may have more serious problems, in particular D-Link (a pump that are, pass away from them) that end up restarting alone or locking with excess traffic, especially if UDP traffic.
What Skype is not wrong, is how P2P works, and even this part of the Skype contract (one that nobody reads). VoIP software with a central server does not have this kind of inconvenience, but need a good central server (or several of them) supernode to the function, and this has a high cost. Skype to put its users as supernodes distributes the cost among them all (obviously who does not like any of this are the telephone companies, in addition to not win with calls made via Skype still has its links more loaded with all connections). For the user this is usually no problem, except for the traffic generated (concern for those with monthly franchises) and the CPU / memory consumption.