telnet <ip> / ssh -l <user> <ip>
Open TCP 23 / 22 to a device — a real connection test: an ACL, a missing route or 'transport input' decides whether it opens. The remote session itself is not simulated.
A firewall's shipped OUTSIDE-IN denies TCP 23, so telnet from outside times out. SSH answers only on a device with RSA keys ('crypto key generate rsa').
Don't just read it — type telnet <ip> / ssh -l <user> <ip> in a real network simulator in your browser and watch it take effect. No install, no account needed to start.
Frequently asked
What does the "telnet <ip> / ssh -l <user> <ip>" command do?
Open TCP 23 / 22 to a device — a real connection test: an ACL, a missing route or 'transport input' decides whether it opens. The remote session itself is not simulated.
What's the common gotcha with "telnet <ip> / ssh -l <user> <ip>"?
A firewall's shipped OUTSIDE-IN denies TCP 23, so telnet from outside times out. SSH answers only on a device with RSA keys ('crypto key generate rsa').