220-1101 Question 60
Single answer23 – TelnetA technician is troubleshooting a legacy network switch that supports remote management only through Telnet. The switch is reachable on the network, but the technician cannot open a remote management session from a Windows workstation. To verify that the Telnet service on the switch is listening and reachable before escalating the issue, which command should the technician use first?
- A
telnet 10.0.0.50 23
- B
ping 10.0.0.50 -p 23
- C
ssh 10.0.0.50 23
- D
ipconfig /renew 10.0.0.50
Show answer and explanation
Correct answer: A
Explanation
Telnet uses TCP port 23 by default and is a legacy, unencrypted remote terminal protocol sometimes still found on older network devices. In a real support scenario, a technician may use the Telnet client to test whether a device is listening on port 23 and accepting connections. This aligns with common troubleshooting practice: first verify network reachability, then verify the specific service and port. While Telnet remains relevant for exam objectives and legacy environments, modern best practice is to prefer SSH for secure remote administration because Telnet transmits data, including credentials, in plaintext. References: IANA service name and port number registry identifies Telnet on TCP 23; common vendor and Microsoft documentation distinguish Telnet from SSH and note Telnet Client as a feature that can be used for testing connections to TCP services.
- A. Correct.
Correct. Using "telnet 10.0.0.50 23" attempts to open a Telnet session to the device on TCP port 23, which is the default Telnet port. This is a practical way to verify whether the remote host is accepting connections on the Telnet service. If the connection opens or prompts for login, the service is reachable; if it fails, the technician has useful evidence for further troubleshooting.
- B. Incorrect.
Incorrect. Ping uses ICMP, not TCP, and it does not test whether TCP port 23 is open. The "-p" switch in common Windows ping usage is not used to test an application port in this way. A device can respond to ping while Telnet is unavailable, or Telnet can be available even if ICMP is filtered.
- C. Incorrect.
Incorrect. SSH and Telnet are different remote access protocols. Although SSH is commonly used instead of Telnet for security reasons, trying SSH to port 23 does not properly test whether a Telnet service is listening. SSH normally uses TCP port 22 and requires an SSH server on the target device.
- D. Incorrect.
Incorrect. "ipconfig /renew" is used to request a new IP configuration from a DHCP server for the local workstation. It does not test connectivity to a remote host's Telnet service and does not accept a remote IP address in this manner.