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A month ago I moved and made a new contract with a new ISP (Claro Peru). Since I switched from ISP I noticed that my connections to servers are always cut after 5 minutes of inactivity (Connections to ports 20, 22, 5432, 3306). This happens on my two computers (linux mint eth-interface, ubutu wlan interface). How can I determine if it is the ISP or the modem-router(device) that makes these cuts?

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Its pretty difficult to do. There are a few things to understand to help -

  • IP packets are packet switched, meaning changes in routing may have a temporary effect on connection but won't break them.

  • NAT rewrites the IP (typically the source IP) - and a change to IP address will break your connection. Connection tracking tables overfilling can also.

  • Many ISPs use Carrier Grade NAT. This can break your connection.

  • It is possible (but a lot less likely) that TCP connection are deliberately being closed by a router sending packets (FIN or RSTpackets I think).

If you check your router WAN interface and it has an address starting 100.64 (or 10. or 192.168 or 17.16-31.) Then your ISP is deploying some kind of NAT and is most likely the culprit.

If the timeout is fairly consistent and/or happening even if you are the only one using your Internet connection, and you are only doing 1 type of thing, the chances become very high that its an ISP fault.

You can try an alternative router recommended by your ISP and if the problem goes away , well, it was your router. If you are using the same router as before and the problem started when you moved ISP its the ISP.

If this fails, it becomes hard. You need to start looking at tcpdumps / data traffic logs in the client and server to see what happened. That takes quite a lot of work.

You can work around the issue by setting up a (for example OpenVPN) VPN between your computer and server. In this way the connection the VPN uses can fail and restart the connection to the server will continue - this is true even if you move between ISPs! VPN abstracts your connection to your provider from your connection to the server.

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  • [i.imgur.com/Zb6M0zq.png] So. This a CG NAT Connection. May 12, 2020 at 21:00
  • Based on the Internet vlan being in the 10.168 network, your ISP is incompetent, and is most likely the cause of the issue. (They should not be using 10.x.x.x to connect to you except by mutual agreement. Arguably they are not even doing proper CARRIER grade NAT because they are in breach of RFC6598 section 3.
    – davidgo
    May 12, 2020 at 22:10
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Use BitviseSSHClient instead. It auto reconnects.

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