On several machines in a corporate SI, telnet is not installed, so your usual telnet HOST PORT command is not working.
You can replace that with a netcat command :
[root@dn25 ~]# nc -z nn.fqdn.com 8020
Connection to nn.fqdn.com 8020 port [tcp/intu-ec-svcdisc] succeeded!Hint : use the -u option to specify a UDP port.