Sunday, 27 January 2013

Problem with SFTP after new router installation

Problem with SFTP / SSH after new router installation

This may seem like an obvious one but it can catch you out if you are not aware of the implications of having a new IP address assigned to your house's broadband. You may have moved your laptop to a new house or using a new wifi system to connect to the Internet.

More commonly you may have been given a new or upgraded router by your ISP provider.

Even if you are told the IP address has not changed by BT, Virgin, Sky, Verizon or whoever is giving you the new router you should do a check on any of the many IP checking pages out there on the web.

E.G this script shows you your current IP and ISP details.


Why is this important?

Well if you have your own server being hosted by a company e.g a cloud server somewhere and you have installed DENY HOSTS to block hacking attacks then you might find that you cannot SFTP (Secure FTP) into your server anymore or that using Putty and SSH to access your remote server suddenly stops working for no apparent reason. Obviously you want to access your server so the problem needs fixing.

Symptoms of an IP change causing problems include:
  • Your server reporting error messages such as "server unexpectedly closed the connection."
  • When you change the file transfer settings to simple FTP from SFTP you can access the server but then experience timeout errors or when the list directory command is run nothing happens.
  • Not being able to use Putty or another SSH tool to connect to your server.
  • Not having changed any settings on your computer but not being able to connect to your server anymore.

Solution to IP change:
  • Check and write down your new IP address.
  • Log into your server through WebMin or a web based system or from another computer that hasn't had an IP change.
  • Check your DENY HOSTS list to see if your IP address is listed and if so delete the record.
  • Add your new IP address in the ALLOW HOSTS list.
  • Re-start your server. 

If you don't know how to do this read the 3rd part of my Wordpress Survival Guide about security.

1 comment:

Asava Samuel said...

This is a reasonable priced SFTP Library you can use with VB.NET:
https://www.kellermansoftware.com/p-41-net-sftp-library.aspx