CentOS - Sep 2012 - ssh_exchange_identification: Connection closed by remote host

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).

TIA,
Marco

(*) except remove the server entry from .ssh/known_hosts in my home
desktop. I did it and nothing changed

M. Fioretti wrote:
>
> 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
<snip>
This would be obnoxious, but have you checked with your ADSL provider, to
see if they're blocking ssh traffic?

      mark

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

Am 14.09.2012 um 17:09 schrieb M. Fioretti:
> 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


Check your tcp_wrapper configuration (/etc/hosts.allow, /etc/hosts.deny).

--
LF

>> On Fri, 14 Sep 2012 17:09:46 +0200 (CEST), 
>> "M. Fioretti" <mfioretti at nexaima.net> said:
M> Yesterday I completed (fingers crossed) the switch to a different ADSL
M> provider. From the moment I turned on the modem on the new ADSL line, I
M> became unable to ssh into server A. All attempts abort with this
M> message:
M>    ssh_exchange_identification: Connection closed by remote host

   This is in the "grasping at straws" category, but have you tried
   connecting with a different cipher, like "blowfish" or
"3des-cbc"?

   If/as/when you get access to the server, can you disable TCP checksum
   offloading?

   root# ethtool -K eth0 tx off rx off
   root# ethtool -t eth0 offline             # adapter self-test

-- 
Karl Vogel                      I don't speak for the USAF or my company
A sum of accountants     --collective nouns, June 1999 LINGUIST