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Hi. Is there anyone out there who has worked for an ISP, or is well-studied, and knows anything general about how ISPs filter ports?

The reason I ask is because it seems like it may be giving me problems. For example, a few months ago, I switched ISPs, and suddenly lost my ability to successfully connect to the FICS server (a popular chess server). I can connect to FICS, it seems, from anywhere else in the world but my own network.

On a more recent and serious note, I've been having some problems with SSH port forwarding. I use dynamic dns and ssh to connect into one of my in-house testing servers. I typically use a custom port in the 4000-5000 range (an arbitrary choice). I'm able to connect consistently from some networks, but from other locations the connection always times out. This is a real pain because that SSH connection will be really valuable to me if I can get it to work consistently.

If anyone has any suggestions or insights, or could point me to some good reading, I'd appreciate it.

PerlCoder (http://www.indicium.us)

Quote Shashank Sharma:

Who's you ISP? These links might help:

Quote Shashank Sharma:

http://answers.yahoo.com/question/index?qid=20080503050628AA1ixnP
http://www.linux.com/feature/55541

Thanks for the reply. After I posted this, I realized it was a pretty silly post (as I often do about five minutes after I post). I should be asking my ISP, not you guys, what ports my ISP filters.

Anyway, my ISP is ACS (Alaska Communications Systems).

I found that I'm able to connect to my home LAN from more places than I am not able to. I suspect now that this doesn't have so much to do with my ISP, as it does with the security measures and port filtering that takes place at the individual networks I use. (For example, I can't connect when I am on my university network, but I can when I am downtown...) I also have been able to connect at more locations using server hopping (connecting to one SSH server, then using it to connect to my home LAN).

I suspect it might also help if I were to use higher port numbers -- in the dynamic range instead of the registered range.

I still think ACS is behind my loss of FICS connectivity, so I'll probably call tech support and ask them about it.

PerlCoder (http://www.indicium.us)