So the other day I needed a quick and easy way to test L4 comms to a server from a guest wireless segment. I purchased a new Macbook earlier this year (a support unix based OS just works best for networking IMO) and MacOS has the netcat tool built into the cli. To use it open terminal and type ‘nc’.

Onto the scenario – we moved a datacentre over the weekend and our WAN provider changed out the router and accidentally missed out a permit statement in the WAN-IN ACL for the guest wireless network. This meant no one could access the Cisco ISE captive portal.

So after I had the ISP add the ACL back in I used the nc command on MacOS to verify layer 4 communications to the Cisco ISE server captive portal port which is TCP/8443 like so:

nc -zv 8443

‘z’ scans for listening daemons and does not send any data just connects to the port and ‘v’ sets the output to verbose. In this case the ACL had been updated and the output comes back as successful:

MacOS Terminal