Random Errors

Putty Fatal Error:
Network Error: Software caused connection to abort.
PuTTY Fatal Error

I worked with CentOS servers from Windows PCs, and I had the same problem with PuTTY. A session didn't last more than 1-5 minutes. I tried to play with PuTTY settings (keepalives, etc.) but it didn't help at all.

Finally I have found the solution for my case. I've recorded TCP dumps both on the client and the server. I've discovered that during 25-30 seconds before disconnecting there are several retransmissions of TCP segments in the client's dump (both from the client's and from the server's side) and finally PuTTY sends RST and close the session with that error. In the server's dump I didn't see any segments from the client in this period, even RST. It means that time to time no TCP segments from the client are delivered to the server and this period is about 30-60 seconds. I've recorded the case several times and always there were retransmissions and final RST from PuTTY. Probably somewhere on the route packets were dropped by network equipments.

To make a workaround I've increased the maximal number of data retransmissions from the default value 5 up to 16. It could prevent PuTTY from disconnection too fast. The variable is 'HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\TcpMaxDataRetransmissions'. I've added this variable manually, it wasn't initially defined in the registy of my Windows. It did help! Now I see that PuTTY hangs from time to time, but it always comes back .

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