Check Port on Centos 7 or Redhat 7

Check Firewall setting 
[root@gukapi guk.weblens.co.uk]# firewall-cmd --list-ports
9020/tcp 80/tcp 443/tcp
[root@gukapi guk.weblens.co.uk]# firewall-cmd --list-all
public
  target: default
  icmp-block-inversion: no
  interfaces:
  sources:
  services: ssh dhcpv6-client gukapi
  ports: 9020/tcp 80/tcp 443/tcp
  protocols:
  masquerade: no
  forward-ports:
  source-ports:
  icmp-blocks:
  rich rules:


Check port is listening or not.

[root@gukapi services]# netstat -anp | grep 9020
[root@gukapi services]#
[root@gukapi services]# ps -ef | grep dotnet
root     10000  8127  0 15:08 pts/1    00:00:00 grep --color=auto dotnet


Start the application

[root@gukapi guk.weblens.co.uk]# dotnet WhatsApp.API.d
WhatsApp.API.deps.json  WhatsApp.API.dll
[root@gukapi guk.weblens.co.uk]# dotnet WhatsApp.API.dll
Hosting environment: Production
Content root path: /root/dotname/gukapi/guk.weblens.co.uk
Now listening on: http://localhost:9020
Application started. Press Ctrl+C to shut down.

Check Port again & We can also test with telent command.

 --- Using netstat
/etc/firewalld/services
[root@gukapi services]# cd /root/dotname/gukapi/guk.weblens.co.uk
[root@gukapi guk.weblens.co.uk]# netstat -anp | grep 9020
tcp        0      0 127.0.0.1:9020          0.0.0.0:*               LISTEN      10018/dotnet
tcp6       0      0 ::1:9020                :::*                    LISTEN      10018/dotnet
[root@gukapi guk.weblens.co.uk]#

  --- Using Telnet
[root@gukapi guk.weblens.co.uk]# telnet localhost 9020
Trying ::1...
Connected to localhost.
Escape character is '^]'.