Title: What are elasticsearch node network stats?
Tags: elasticsearch
Question: When I get node stat in es with curl, the response is ;

```curl -XGET 'http://localhost:9200/_nodes/stats/network?human&amp;pretty'

{
  "cluster_name" : "elasticsearch",
  "nodes" : {
    "XpAeeHs6Q7WxycqJBOShfA" : {
      "timestamp" : 1411385146836,
      "name" : "Ape-X",
      "transport_address" : "inet380-562-5705:9300]",
      "host" : "test",
      "ip" : [ "inet380-562-5705:9300]", "NONE" ],
      "network" : {
        "tcp" : {
          "active_opens" : 93920,
          "passive_opens" : 39,
          "curr_estab" : 62,
          "in_segs" : 7053825,
          "out_segs" : 4536915,
          "retrans_segs" : 4948,
          "estab_resets" : 1572,
          "attempt_fails" : 523,
          "in_errs" : 708,
          "out_rsts" : 48488
        }
      }
    }
  }
}
```

I checked it with "netstat -anlp" command. There was not any connection to 9200 or 9500 ports. However "curr_estab" is 62. Does "curr_estab" show current established network? I looked in documentation for parameters "active_opens", "passive_opens" and  "curr_estab" but I couldn't find any. What these parameters represents in elasticsearch?



Here is another answer: ```
Active and Passive OPENs
TCP/IP is based on the client/server model of operation, and TCP connection setup is based on the existence of these roles as well. The client and server each prepare for the connection by performing an OPEN operation. However, there are two different kinds of OPEN:
Active OPEN: A client process using TCP takes the “active role” and initiates the connection by actually sending a TCP message to start the connection (a SYN message).
Passive OPEN: A server process designed to use TCP, however, takes a more “laid-back” approach. It performs a passive OPEN by contacting TCP and saying “I am here, and I am waiting for clients that may wish to talk to me to send me a message on the following port number”. The OPEN is called passive because aside from indicating that the process is listening, the server process does nothing.
A passive OPEN can in fact specify that the server is waiting for an active OPEN from a specific client, though not all TCP/IP APIs support this capability. More commonly, a server process is willing to accept connections from all comers. Such a passive OPEN is said to be unspecified.
```


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