How can Bit-torrent listen from a port which is closed?

[addzy94]

My ISP blocks all ports except for port 80 as far as I know. How do I know this? I asked them. Why do they do this? They want me to pay extra CASH for a static IP. I know...they suck. I have never been able to port forward to use any of the applications that require it.

I confirmed this on http://

My question is different.

I can see that my port - 8999 which Bittorrent uses (We can choose any port we want) according to Bitorrent is closed.

Port 8999 is shown as closed for my public IP on the above website. However, data still gets through and I can upload as well to fellow peers.

How is this happening? I am very much interested. I'm also studying Computer Networks, so I know a bit about this stuff as well...like TCP and UDP framework, peer churn, etc.

 

[BadActor]

I would have to say their "blocking" is not working, regardless of how they are implementing it. I can't give you a specific answer to your question, however I can tell you that in the settings for your client, choosing Randomize Port on each startup and then enabling encryption can help keep you from being throttled by your ISP if they can't tell the difference between streaming and torrenting. Some are more sophisticated and will be able to tell, but it works for many.

 

[triley]

Your ISP can not block those ports without breaking the internet. When you browse the internet you are contacting port 80 on the remote web-server but your computer is sending a randomly assigned port number between 1024 and 65535 for the return address. That random port number is what your pc (or router if using nat) is listening on. If the isp blocks those ports you would never get data from the web-server.

 

[addzy94]

I know they are blocking ports successfully because other applications that require port forwarding do not work. Are you saying that my Torrent is running through port 80? That is not possible because 80 is for HTTP. As far as I know that is the ONLY port that is open. Is it even legal for ISP's to block all other ports and just provide 1 port?

 

[BuddhaSkoota]

I know they are blocking ports successfully because other applications that require port forwarding do not work. Are you saying that my Torrent is running through port 80? That is not possible because 80 is for HTTP. As far as I know that is the ONLY port that is open. Is it even legal for ISP's to block all other ports and just provide 1 port?

Port 80 is an outbound port, not used when you are browsing the web. Inbound port 80 is normally used when you are running your own webserver.

To which ISP are you subscribed? You were likely given incorrect information about all ports being blocked.

You do not need a static IP address to utilize port forwarding. The problem you are having with port forwarding is more likely a configuration issue.

 

[addzy94]

They never said anything about all ports being blocked when I subscribed to them. It's some local ISP which has teamed up with a Cable service provider. You, and people who are like 10 kilometers away, from where I'm sitting right now wouldn't have heard of them. They don't even have a website. But Unlimited 15MBps of Fiber Optic goodness is a pretty sweet deal. That's why I chose them. Should have known that there were other compromises to be made.

How can they forward the port for me if my IP changes as I don't have a static one. Can it be mapped dynamically to the Username of the Client instead of IP Address, so that the port is automatically opened when some IP is assigned to me from their end?

I have port forwarded through my router. I am sure I have done everything right.

 

[BuddhaSkoota]

It seems that BitTorrent allows you to specify a starting port, but it will actually scan from that point to find a usable port. Port 8999 is likely not the actual port being used. You should be able to find the port in use through Resource Monitor (if using a Windows OS) or other network monitoring tool.

How can they forward the port for me if my IP changes as I don't have a static one. Can it be mapped dynamically to the Username of the Client instead of IP Address, so that the port is automatically opened when some IP is assigned to me from their end?

That depends on your ISP's network management capabilities. It is not difficult for an ISP to manage ports on individual accounts based on a customer's network ID, but a less sophisticated operator may not have the knowledge or resources to do so.

If you feel that you have done everything possible from your standpoint, only your ISP can assist you in resolving further port issues.