anchor.diff:  `sysctl net.ipv4.tcp_retries2`.
   
   IMPORTANT: This setting applies to all TCP connections and will affect the
  -reliability of communication with systems outside your cluster too. If your
  -cluster communicates with external systems over an unreliable network then you
  +reliability of communication with systems other than {es} clusters too. If your
  +clusters communicate with external systems over a low quality network then you
   may need to select a higher value for `net.ipv4.tcp_retries2`. For this reason,
   {es} does not adjust this setting automatically.
   
  
positive.code: You must also ensure your network infrastructure does not interfere with the
  long-lived connections between nodes, <<long-lived-connections,even if those
  connections appear to be idle>>. Devices which drop connections when they reach
  a certain age are a common source of problems to Elasticsearch clusters, and
  must not be used.
  
  
negative.code: [[system-config-tcpretries]]
  === TCP retransmission timeout
  
  Each pair of {es} nodes communicates via a number of TCP connections which
  <<long-lived-connections,remain open>> until one of the nodes shuts down or
  communication between the nodes is disrupted by a failure in the underlying
  infrastructure.
  
  TCP provides reliable communication over occasionally unreliable networks by
  hiding temporary network disruptions from the communicating applications. Your
  operating system will retransmit any lost messages a number of times before
  informing the sender of any problem. {es} must wait while the retransmissions
  are happening and can only react once the operating system decides to give up.
  Users must therefore also wait for a sequence of retransmissions to complete.
  
  Most Linux distributions default to retransmitting any lost packets 15 times.
  Retransmissions back off exponentially, so these 15 retransmissions take over
  900 seconds to complete. This means it takes Linux many minutes to detect a
  network partition or a failed node with this method. Windows defaults to just 5
  retransmissions which corresponds with a timeout of around 6 seconds.
  
  The Linux default allows for communication over networks that may experience
  very long periods of packet loss, but this default is excessive and even harmful
  on the high quality networks used by most {es} installations. When a cluster
  detects a node failure it reacts by reallocating lost shards, rerouting
  searches, and maybe electing a new master node. Highly available clusters must
  be able to detect node failures promptly, which can be achieved by reducing the
  permitted number of retransmissions. Connections to
  <<modules-remote-clusters,remote clusters>> should also prefer to detect
  failures much more quickly than the Linux default allows. Linux users should
  therefore reduce the maximum number of TCP retransmissions.
  
  You can decrease the maximum number of TCP retransmissions to `5` by running the
  following command as `root`. Five retransmissions corresponds with a timeout of
  around six seconds.
  
  [source,sh]
  -------------------------------------
  