220-1101 · Question #15
A software firewall that blocks all network ports has been installed on a desktop computer. The computer is now unable to get a dynamic IP address. Which of the following ports need to be opened on th
The correct answer is B. 67, 68. To obtain a dynamic IP address, a computer needs to communicate with a DHCP server, which uses UDP ports 67 and 68.
Question
A software firewall that blocks all network ports has been installed on a desktop computer. The computer is now unable to get a dynamic IP address. Which of the following ports need to be opened on the firewall?
Options
- A25, 110
- B67, 68
- C80, 443
- D161, 162
How the community answered
(31 responses)- A3% (1)
- B94% (29)
- C3% (1)
Why each option
To obtain a dynamic IP address, a computer needs to communicate with a DHCP server, which uses UDP ports 67 and 68.
Ports 25 (SMTP) and 110 (POP3) are used for sending and receiving email, respectively, not for obtaining an IP address.
DHCP (Dynamic Host Configuration Protocol) servers listen on UDP port 67, and DHCP clients send requests on UDP port 68. Opening these ports allows the client to send DHCP Discover/Request messages and receive DHCP Offer/ACK messages from the server, thus obtaining a dynamic IP address.
Ports 80 (HTTP) and 443 (HTTPS) are used for web browsing, not for DHCP address assignment.
Ports 161 (SNMP) and 162 (SNMP Trap) are used for network device management, not for dynamic IP address assignment.
Concept tested: DHCP ports for dynamic IP address assignment
Source: https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml
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