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I've run into a problem with ssh that has me completely stumped (and our department IT guy as well): Up until a few days ago I had no problems accessing my files on our departmental server (university math department, running Scientific Linux) using SSH from my Ubuntu box at home, and I had no problems mounting my user directory at work as a network drive.

As of a couple of days ago, running ssh [email protected] returns

ssh_exchange_identification: Connection closed by remote host

Running ssh -v hostname.tld returns

OpenSSH_6.1p1 Debian-4, OpenSSL 1.0.1c 10 May 2012

debug1: Reading configuration data /etc/ssh/ssh_config   
debug1: /etc/ssh/ssh_config line 19: Applying options for *  
debug1: Connecting to gorilla.math.uwo.ca [129.100.75.10] port 22.  
debug1: Connection established.    
debug1: identity file /home/sean/.ssh/id_rsa type -1  
debug1: identity file /home/sean/.ssh/id_rsa-cert type -1  
debug1: identity file /home/sean/.ssh/id_dsa type -1  
debug1: identity file /home/sean/.ssh/id_dsa-cert type -1  
debug1: identity file /home/sean/.ssh/id_ecdsa type -1  
debug1: identity file /home/sean/.ssh/id_ecdsa-cert type -1  
ssh_exchange_identification: Connection closed by remote host  

and trying to mount the network folder gives

Oops! Something went wrong. Unhandled error message: SSH program unexpectedly exited

In fact I'm not even able to successfully ping the server.

My first thought was that either the server was down, or I had some sort of incorrect firewall setting (although I had not made any changes to the firewall or router). It's not a problem connecting via SSH through my router/firewall though, since I can connect to other servers via SSH (I still have access to my account on the server at my last department), and the server I want to connect to is still up, since I can connect as follows: 1. SSH into old server. 2. From old server, SSH into new server.

However, I can't log into the new server directly. I'm completely stumped. Any ideas?

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1 Answer 1

I frequently use services like fail2ban or denyhosts to monitor for invalid login attempts (usually dictionary attacks) and ban the clients' addresses.

They typically work by adding the client address to /etc/hosts.deny, at which point you'll see the types of failures you're describing here, including the "ssh_exchange_identification: Connection closed by remote host" message when using ssh -v .

It's worth checking whether your client address is in /etc/hosts.deny and if a service like denyhosts is running.

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Thanks. I've sent my current IP address to the guy running our server to see if it's been blacklisted. The only guess we've come up with so far is that I was assigned a new dynamic IP address from my ISP, and they gave me one that was previously banned for port scans or repeated login failures, since everything worked fine until a few days ago. –  Sean Fitzpatrick Oct 2 '13 at 3:14

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