N10-009 Question 63
Single answerTFTP: 69A network administrator is staging several new switches in a lab and wants them to download a boot image from a server during the initial provisioning process. The devices are configured to use TFTP for the transfer. The administrator can ping the server successfully, but the image download fails immediately. A firewall between the lab VLAN and the server VLAN was recently tightened to allow only required traffic. Which change is the MOST likely needed to allow the transfer to start?
- A
Allow UDP port 69 from the switches to the TFTP server
- B
Allow TCP port 69 from the switches to the TFTP server
- C
Allow UDP port 161 from the switches to the TFTP server
- D
Allow TCP port 21 from the switches to the TFTP server
Show answer and explanation
Correct answer: A
Explanation
TFTP (Trivial File Transfer Protocol) is commonly used in real-world environments for lightweight file transfers such as boot images, firmware, and configuration files for network devices, especially during PXE or device provisioning workflows. The well-known port associated with TFTP is UDP 69, which is used for the initial client request. On Network+, candidates are expected to recognize that TFTP is connectionless and uses UDP rather than TCP. In practice, administrators should also remember that TFTP is intentionally minimal and lacks authentication and encryption, so it is generally used only in controlled or isolated environments. This aligns with standard protocol references such as IANA service name assignments and vendor documentation for switch/router image transfers.
- A. Correct.
Correct. TFTP uses UDP port 69 for the initial request to the server. In a provisioning scenario where devices are downloading boot images or configuration files, blocking UDP 69 will prevent the transfer from starting. This is the key port commonly associated with TFTP on the Network+ exam.
- B. Incorrect.
Incorrect. TFTP does not use TCP. A common misconception is to assume all file transfers use TCP because FTP does, but TFTP is a much simpler protocol that uses UDP instead.
- C. Incorrect.
Incorrect. UDP port 161 is used by SNMP, typically for management polling and monitoring. It is unrelated to transferring boot images with TFTP, though it is another common network management port that candidates may confuse with TFTP.
- D. Incorrect.
Incorrect. TCP port 21 is used by FTP control connections. FTP and TFTP are different protocols despite both being used for file transfer. TFTP does not use TCP 21 and does not establish an FTP-style control session.