Prevent your computer from becoming a Skype Supernode!

Skype supernodes have made it into the press over the last weeks due to problems in the Skype software, which caused a three day Skype outage on August the 16th. Some people started to ask, “What is a Skype supernode”? Also more interestingly they started asking, “Am I a Skype supernode and if I am, then how do I stop my computer from becoming a Skype supernode in the first place”?

Most users of Skype will be sitting behind a NAT enabled router (network address translation – you’ll have an IP address that starts with 192.168, or 172.30, or 10.0, etc), some users maybe connecting to the internet less securely. In these cases, the Skype P2P network may decide to use your computer as a “supernode”. Supernodes act as middle men between different Skype users, and sometimes the Skype inner core network. More can be read about them on the Skype security website (see below for the network guide).

Obviously there are bandwidth considerations in play here, and although minimal (5 kbyte per second), some users might like to opt out of playing such a role within SkypeNet. Without supernodes however, the Skype network would not function well well at all, therefore Skype does not offer a direct user interface to disable the use of your computer as a supernode through the program. However, there is a way around this.

Skype outlines several guidelines as to prevent your computer becoming a supernode on their security website under the “Universities Section“. Skype publishes a “Skype Guide for Network Admins“, mainly so that large networks such as those in universities and corporations can restrict certain Skype functions through network user policies. If the suggestions in the universities section don’t help then there is a fallback. This is done through a series of Windows Registry Keys.

Furthermore, the guide notes that certain supernodes maybe promoted to “Relay Hosts”, which take on further network responsibility, including the relaying of file transfers, voice and video calls. If you have ever waited ages for a small file to be transferred between you and a colleague, it is probably because one of you is being relayed – Skype can’t establish a direction connection between the two of you (see PortForward.com to help you configure your router for optimal Skype usage). Removal of you as a supernode means that you can never be promoted to relay host either, so let’s get on and delve in further.

As ever, if you don’t know what you are doing with the Windows Registry then leave it well alone. You could cause unrecoverable damage, but if you know your way around the registry then the instructions for restricting your computer from becoming a supernode can be found on the last page of the Skype Guide mentioned above. The specific registry key you will need to create is:

There are several other useful keys described there, notably the use of HTTP ports, which can be a pain if you develop web software using http://localhost. This seems to be partially duplicated in the Skype user interface under Tools – Options – Advanced – Connections, with the checkbox that says “Use port 80 and 443 as alternatives for incoming connections”. The different is that is you set the registry key the checkbox will become disabled (locked) and you will not be able to alter the setting via the user interface.

Let me know if this helped anyone.