[CentOS] ssh_exchange_identification: Connection closed by remote host

[Dennis Jacobfeuerborn]

On 09/14/2012 05:09 PM, M. Fioretti wrote:
> Greetings,
> 
> I have accounts on two Centos servers, A and B, each hosted on a remote
> VPS by a different provider/datacenter.
> 
> Until yesterday night, I could connect without problems via SSH to both
> servers from my home Fedora 16 desktop.
> 
> Yesterday I completed (fingers crossed) the switch to a different ADSL
> provider. From the moment I turned on the modem on the new ADSL line, I
> became unable to ssh into server A. All attempts abort with this message:
> 
> ssh_exchange_identification: Connection closed by remote host
> 
> I know that server A is still up and running, because the websites and
> email services it runs are still up. Server B is still reachable via ssh,
> no problem. The only difference between the two servers is that A runs
> Centos 4.something, while B runs Centos 6.1
> 
> I have already done some online search on this problem, but all the pages
> I have found discuss how to diagnose and fix it working on the server (*),
> which is exactly what I can't do right now...
> 
> Any clues on what may have happened, and if it could be related in any way
> to differences (whatever they may be) between ADSL providers, instead of a
> bizarre coincidence?
> 
> Of course, I can and will ask the VPS provider to reboot the machine, but
> I would also like to know your opinion on what exactly may have happened,
> and how to prevent it in the future (also to pass your suggestions to the
> provider).

Check the /var/log/secure log. It could be that some bot is trying to brute
force your server and the daemon is hitting the session limit.

Regards,
  Dennis