Problem is now solved. Torrents seem to seed, although very infrequent, but it works.

The culprit was that my ISP uses CGN (Carrier-grade NAT) so I'm technically in my ISP's local network with no ports open.

I'm applying for a static public IP and I hope that solves my problem.

I've recently been upgraded from a 3.5/0.5mbit ADSL connection to a 1000/1000mbit fiber connection. With this upgrade I'm able to download and seed a lot, but I'm having problems seeding with my client, especially private trackers. Download is quite fast, around 14MB/s on a good torrent. Upload is u...