I am frequently encountering the "Remote side unexpectedly closed network connection" error while attempting to maintain a stable SSH session to my remote servers. This disruption usually happens during long-running data transfers or while deploying updates. Is this likely a timeout issue within my local client configuration, a firewall restriction on the server side, or perhaps an MTU size mismatch within the VPC? I need a reliable way to keep these sessions alive without constant drops.
3 answers
This error is incredibly common when the server or an intermediate firewall (like an AWS Security Group or Azure NSG) terminates an idle connection. To fix this, you should modify your local SSH config file by adding ServerAliveInterval 60 and ServerAliveCountMax 3. This forces your client to send a "ping" to the server every minute, ensuring the connection stays active. On the server side, you can also check the sshd_config for ClientAliveInterval settings. If you’re using a VPN, ensure that the MTU settings aren't causing packet fragmentation, which often leads to these sudden closures during high-traffic tasks.
Have you checked your server's system logs, specifically /var/log/auth.log or journalctl, to see if the SSH daemon is actually the one killing the process due to a specific security policy?
I usually see this when the idle timeout is too low. Try setting your SSH client to send keep-alive packets every 30 seconds; it usually stops the network from dropping the connection.
I agree with Joshua. Keeping the connection "warm" with frequent packets is the most effective way to bypass aggressive firewall idle-timeout policies that we see in modern cloud architectures.
Thanks for pointing that out, Christopher. I checked the logs and I see several 'timeout' entries but no explicit 'refused' errors. If the logs show the connection was terminated by the host, does that imply the issue is definitely with the server-side configuration, or could a load balancer in front of the instance still be the culprit for closing the TCP handshake prematurely?