Using telnet from the VMware 5.x ESXi shell

The short answer is: you can't use telnet. But you can use alternatives, obviously.

For instance, to troubleshoot some iSCSI connectivity problems, you would be used to doing something as this.

~ # telnet 10.0.2.3 3260
-ash: telnet: not found

Instead, you can use netcat to test the connectivity.

~ # nc -z 10.0.2.3 3260
Connection to 10.0.2.3 3260 port [tcp/*] succeeded!

If you were to test this on a closed TCP port, the error would look like this.

~ # nc -z 10.0.2.3 32600
(empty response)