Will es nodes connect with each other in 9200?

[JohnPhilip]

Hi, there.
The official doc said,

Each Elasticsearch node has two different network interfaces. Clients send requests to Elasticsearch’s REST APIs using its HTTP interface, but nodes communicate with other nodes using the transport interface. The transport interface is also used for communication with remote clusters.

So can I understand there will be no traffic of 9200 if there is no external client to access the rest interface?

I was curious about this because I found that when I use

lsof -i:9200

and there are many established connections.

COMMAND   PID          USER   FD   TYPE     DEVICE SIZE/OFF NODE NAME
java    18801 elasticsearch  360u  IPv4 4246429501      0t0  TCP strees:wap->10.10.6.15:35059 (ESTABLISHED)
java    18801 elasticsearch  561u  IPv4 4179746514      0t0  TCP *:wap (LISTEN)
java    18801 elasticsearch  578u  IPv4   63089845      0t0  TCP strees:wap->10.10.20.116:51088 (ESTABLISHED)
java    18801 elasticsearch  612u  IPv4 4184040085      0t0  TCP strees:wap->10.10.20.31:64112 (ESTABLISHED)

what are they used for?

[JohnPhilip]

After use tcpdump I found it's monitoring data(I also deploy a kibana in my environment), and I found that there already described that What are ports 9200 and 9300 used for?

• Port 9200 is used for all API calls over HTTP. This includes search and aggregations, monitoring and anything else that uses a HTTP request. All client libraries will use this port to talk to Elasticsearch

So it is the monitoring request cause this.
Sorry for disturbance.