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I have a really strange problem, it's so strange for me that I cannot deal with it. I was working on site development on a 1und1.de server then one day I decided to try ssh, I probably made too many failed attempts. Now I have this situation:

  • I can't connect to my-developed-domain.com from my PC
  • I can't connect to my-developed-domain.com from my MAC
  • I can't connect to my-developed-domain.com from my ANDROID PHONE

What i CAN:

  • I CAN connect to my-developed-domain.com from my PC using PROXY
  • I CAN connect to my-developed-domain.com from my MAC using PROXY
  • I CAN connect to my-developed-domain.com from my wife's phone
  • I CAN connect to my-developed-domain.com from my wife's laptop

What is this? How is this possible? When it fails I see ERR_CONNECTION_TIMED_OUT

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    It's not clear from your question whether this is HTTP (or HTTPS) or SSH you're talking about. Also you're not telling us if all those connections are from the same local network, or from different networks (e.g. home/work, or DSL vs 3G, etc.).
    – jcaron
    Jan 19 '16 at 12:50
  • same LAN, HTTP just normal site browsing
    – Ponciusz
    Jan 19 '16 at 13:18
  • Have you tried clearing cache and/or cookies on the devices where it doesn't work? Can you confirm that they correctly resolve the domain name to the right IP address (use dig, nslookup or even ping to see the IP address used, both of the computers where it works and on those where it doesn't. I suppose your LAN is being a NAT router (i.e. it's all going through a single public IP address)?
    – jcaron
    Jan 19 '16 at 13:25
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This sounds like a server firewall issue. Failed ssh attempts can usually trigger a rule that will then block your IP.

1und1.de has a guide for how to manage their server firewall (I had to use Google Translate to read it). You may be able to log in to your server control panel to whitelist your IP. If not, you could try getting in touch with 1und1.de hosting support.

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The first thing that I would check is DNS. It sounds like you recently changed your DNS settings and it has not completely propagated yet. When you change DNS settings it may take several days for the changes to fully take effect depending on your time to live (TTL) settings. Some computers will see the new info sooner than others. Computers that have not connected to the website recently (presumably like your wife's devices and your proxy) will get the new information faster because it is less likely to be cached by the DNS server.

Use tools like ping and dig from your various computers and see what IP address each thinks that the website is on. If the values differ, you know that a cached version of the IP address in DNS is the problem.

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  • Keep in mind that TTL times do now always come fully into play. Some ISPs cache DNS entries only once a week and others pull only periodically. One well known ISP used to cache only once a month recently, though finally updated their mechanism to something more reasonable in 2015. Crazy huh??
    – closetnoc
    Jan 20 '16 at 0:32

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