Test Tcp Open Port

If you don”t have telnet or nc installed and want to quickly test firewall traffic to a server and specific port you can try this. It needs a new enough bash but still pretty quick and handy.

Good test port is open

1
$ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/172.18.10.66/1521'
2
$ echo $?
3
0

Port not open

1
$ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/172.18.10.66/15'
2
$ echo $?
3
124

Good test port is open to google FQDN

1
$ timeout 1 bash -c 'cat < /dev/null > /dev/tcp/google.com/80'
2
[opc@ocilxeasdbt02 ~]$ echo $?
3
0