In a recent post, Om points out to a site (originally identified in Skype Journal) that plots Skype supernodes around the world. He also points out that these supernodes are a source of concern in many organizations and that some products and home cooked schemes have sprung up to address this. If there is conscription, people will find ways to avoid it. Some will learn to say “zed” and move north; but then some register for higher studies and avoid it. In other words, can one continue to use Skype but avoid becoming a supernode or a relay node?
For some time I was under the impression that if the client is behind a NAT/FW then it will not be a candidate. But in reality this is not the case. If the device is behind a well “behaved” NAT, then it effectively has a public IP address/port and so is reachable by others. This means that such devices can be used as supernodes. So the only effective way is to place the Skype client behind a symmetric NAT. One of the questions Skype Journal asks is “Why are Chinese Skype supernodes not shown on the map? Where else are these factors at play?” I think I know the answer. I am told (and I have no way to verify) that Chinese ISPs deploy their own symmetric NATs. This probably explains the absence of supernodes in China.
There is another interesting observation. Om refers to a mailing list post that describes a simple and open way that an enterprise can block Skype. Given this, I wonder what is so special about Verso, which got written up in Wall Street Journal among others.
Posted by aswath at December 9, 2005 11:15 PM