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--- en:dpi:opt_cgnat:faq:cgnat_faq_3 [2023/08/28 14:08] – ↷ Page moved from en:dpi:opt_cgnat:cgnat_faq:cgnat_faq_3 to en:dpi:opt_cgnat:faq:cgnat_faq_3 elena.krasnobryzh
+++ en:dpi:opt_cgnat:faq:cgnat_faq_3 [2023/08/28 14:18] (current) – removed elena.krasnobryzh
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-====== Idle (inactive) SSH sessions began to get disconnected after enabling NAT ======
-{{indexmenu_n>3}}
-Indeed, the NAT session lifetime is limited, since the subscriber sessions number is a limited resource and a large number of idle (inactive) sessions in the pool reduces NAT performance and consequently the total performance.
-NAT doesn't have the ability to distinguish whether the session was terminated abnormally or is simply inactive, so NAT closes such sessions because inactivity timeout has been exceeded. Such a behavior is provided by the standard and is supported by most CG-NAT vendors.
-Sessions lifetime in Stingray SG can be configured by followin settings
-<code>
-lifetime_flow=60
-lifetime_flow_long=600
-</code>
-where lifetime_flow_long is a lifetime in seconds of inactive TCP-sessions, lifetime_flow regards the remaining TCP-sessions.
-<note warning>The values of reviewed above settings should not be too high, since it can cause CG-NAT performance reduction due to enormous session table, also it can cause the subscriber session limit being exhausted (is set by nat pool settings).</note>
-Therefore, it is recommended to use tcp keep-alive mechanism when the long-running inactive connections take place, it means that the empty packet will be sent regularly within the session which indicates the session still active.
-You can configure tcp keep-alive either application-wide on the server or client side, or operating system-wide at once.
-**SSH server setting example**
-<code>
-in /etc/ssh/ssh_config file add the following line
-ServerAliveInterval 60
-</code>
-**SSH clien-side setting example**
-<code>
-in ~/.ssh/config file add the following lines
-Host *
-  ServerAliveInterval 60
-</code>
-<code>
-or using terminal
-ssh -o TCPKeepAlive=yes -o ServerAliveInterval=60 user@example.com
-</code>
-**System-wide setting example for the CentOS**
-<code>
-in /etc/sysctl.conf file add the following lines
-net.ipv4.tcp_keepalive_time = 600
-net.ipv4.tcp_keepalive_intvl = 60
-net.ipv4.tcp_keepalive_probes = 20
-</code>

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