[CentOS] Problem with ssh disconnecting

[H]

On 02/19/2018 10:09 PM, Marcelo Ricardo Leitner wrote:
> On Mon, Feb 12, 2018 at 08:05:18PM -0500, H wrote:
> ...
>> Not sure if I am reading your reply correctly but I should clarify
>> that I have problems when running naked ssh to the server, when I
>> run ssh to the same server but over the VPN connection (that goes
>> via third server) everything is flawless.
>>
>> I should also explain that:
>>
>> - I am on a workstation (located in the US), ssh-ing into server 1
>> (located in the US).
>>
>> - From server 1 I use scp to transfer large files from server 2
>> (located in Europe) to server 1 (in the US).
>>
>> The above randomly disconnects.
> You have two ssh sessions here. AFAICT, it's the first one
> (workstation->server 1) that randomly disconnects, right?
>
>> However, when:
>>
>> - I use a VPN connection to server 3 (also located in Europe).
>>
>> - From the same workstation as above, do exactly as above,
>> connections are rock-solid.
> It would seem to me that something between your workstation and server
> 1 is possibly mishandling TCP options (being it sack, timestamps or
> both).  Is there a router or a firewall in between?
>
> Try doing a traffic capture between both and see why it hangs. If
> you're hesitant to post the binary traffic capture, post the text
> version of it with anonymized IP addresses. Just please be sure to
> disable ssh protocol so it would include TCP details on it then.
>
>   Marcelo

Let's reduce the problem to a simpler case: the workstation running CentOS 7 is behind a router, behind the same router is the server running CentOS 6. For various reasons, I access the server via its external IP address, not the local one. Access is via ssh.

When using straight ssh, the connection times out after random times, always less than 20 minutes or so, though, with the error message "packet_write_wait: broken pipe", not the common "write failed: broken pipe".

However, when I am in a ssh session on a VPN connection (which terminates in an outside server far away from my network), the ssh connection does /not/ time out.

Further, accessing the same server as first mentioned, in the identical fashion, from another computer running CentOS 6, I never encounter the "packet_write_wait" error and disconnection.

My conclusion is thus that this is not a router issue but could conceivable be a bug in CentOS 7. I am also ruling out a cable issue or a physical network card issue since the VPN connection is stable.