source :
http://www.blubster.net/php/article.php?sid=34
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Another thing that can be stopping Blubster is Internet Connection Sharing, ICS. This software is used to share an only internet access to several intranet computers. Unlucky ICS doesn’t handle well UDP transmissions that Blubster needs to perform. ICS and Blubster are incompatible.
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Router users are having a lot of problems to connect with Blubster. This is because when a remote computer sends some data to the UDP port 41170, it arrives to the router, but the router may not be forwarding the data to the computer correctly. Your router will have an IP address, visible to the internet, where all the external data is sent. Your router should then resend this data to the computer -which has another different and private IP- so that your Blubster client can listen to other clients.
What you need to connect to the Blubster network through a router is configuring the Port Forwarding. The configuration steps may vary from a router to other, but the basis is that DATA RECEIVED TO THE PORT 41170 USING THE PROTOCOL UDP MUST BE FORWARDED TO THE IP OF THE COMPUTER RUNNING THE BLUBSTER CLIENT. Some users needed to forward ports from 41170 to 41350.
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Donc en gros, abandonne ICS et partage ta connexion internet autrement (NAT)