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When I start Tomcat I see the following using netstat (filtered by tomcat PID):

TCP    0.0.0.0:5007           xxxx34793KZ:0          LISTENING
TCP    0.0.0.0:8081           xxxx34793KZ:0          LISTENING
TCP    0.0.0.0:8543           xxxx34793KZ:0          LISTENING
TCP    127.0.0.1:8005         xxxx34793KZ:0          LISTENING
TCP    127.0.0.1:29821        xxxx34793KZ:29822      ESTABLISHED
TCP    127.0.0.1:29822        xxxx34793KZ:29821      ESTABLISHED
TCP    127.0.0.1:29823        xxxx34793KZ:29824      ESTABLISHED
TCP    127.0.0.1:29824        xxxx34793KZ:29823      ESTABLISHED
TCP    127.0.0.1:29830        xxxx34793KZ:29831      ESTABLISHED
TCP    127.0.0.1:29831        xxxx34793KZ:29830      ESTABLISHED
TCP    127.0.0.1:29832        xxxx34793KZ:29833      ESTABLISHED
TCP    127.0.0.1:29833        xxxx34793KZ:29832      ESTABLISHED
TCP    127.0.0.1:29834        xxxx34793KZ:29835      ESTABLISHED
TCP    127.0.0.1:29835        xxxx34793KZ:29834      ESTABLISHED
TCP    127.0.0.1:29836        xxxx34793KZ:29837      ESTABLISHED
TCP    127.0.0.1:29837        xxxx34793KZ:29836      ESTABLISHED
TCP    [::]:8081              xxxx34793KZ:0          LISTENING
TCP    [::]:8543              xxxx34793KZ:0          LISTENING

Ports 29821-29824 and 29830-29837 are what I'm wondering about.

I have searched the web, tomcat documentation, tomcat source code and any mailing list I can think of (including Stackoverflow) and can find nothing on the purpose of these TCP ports. They come in pairs which implies to me that they are possibly configured to loopback. I'm stumped as to why Tomcat needs these.

Our application that runs on Tomcat gets installed into environments where IT Security is quite robust, so they want to know the reason for every port in use.

Any ideas?

ScottD
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  • The listening ports are all defined in `server.xml.` The ESTABLISHED connections are all self-connections via 127.0.0.1 and are therefore not any kind of security concern. – user207421 Dec 01 '15 at 02:44
  • Thanks. Any idea why Tomcat needs these self-connections? – ScottD Dec 01 '15 at 16:54
  • I did figure out that each connector defined in server.xml is responsible for 6 of tcp connections (i.e. 3 pairs per connector). We have two connectors defined, http and https. – ScottD Dec 01 '15 at 18:08

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