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Firstly i apologize my English. Our Azure Linux(Ubuntu 16.04.2 LTS) instance has been running for more than a 2 months now. Suddenly tuesday night without any configuration to server, I get randomly "Software caused connection abort" from my automated powershell-script. Script uses Winscp-client for sftp-connection. I get this error randomly in my Putty-client also. Connections to this server are made from multiple servers that are in different networks. We have tried following things:

  1. Checked errors from auth.log and there is nothing special. Increased log level to Debug3
  2. Checked that iptables is disabled
  3. Modified sshd_config-file: -MaxStartups 200 -MaxSessions 200 -UseDNS no
  4. Modified /etc/sysctl.conf with lines:

    -net.ipv4.ip_local_port_range = 1024 65535 -net.core.rmem_max = 16777216 -net.core.wmem_max = 16777216 -net.ipv4.tcp_max_syn_backlog = 4096 -net.ipv4.tcp_syncookies = 1 -net.core.somaxconn = 2048 -net.core.netdev_max_backlog=2000 -kernel.pid_max = 1000000 -fs.file-max = 1000000 -net.ipv4.tcp_sack=0 -net.ipv4.tcp_rmem = 4096 87380 16777216 -net.ipv4.tcp_wmem = 4096 65536 16777216 -net.ipv4.tcp_synack_retries = 2 -net.ipv4.tcp_syncookies = 1 -net.ipv4.tcp_mem = 50576 64768 98152 -net.core.wmem_default = 65536 -net.core.rmem_default = 65536 -net.ipv4.tcp_window_scaling=1 -net.ipv4.tcp_mem= 98304 131072 196608 -net.ipv4.tcp_timestamps = 0 -net.ipv4.tcp_rfc1337 = 1 -net.ipv4.ip_forward = 0 -net.ipv4.tcp_congestion_control=cubic -net.ipv4.tcp_tw_recycle = 0 -net.ipv4.tcp_tw_reuse = 0 -net.ipv4.tcp_orphan_retries = 1 -net.ipv4.tcp_fin_timeout = 25 -net.ipv4.tcp_max_orphans = 8192

How can i begin to resolve this issue? Has somebody has this kind of issue? Can it be somekind of network issue with ISP? I checked server stats and CPU and memory loads are low. Like i said this started tuesday night. Nothing has been changed in server.

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