Ace the CompTIA Server+ (SK0-004) 2026 Challenge

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Clients cannot connect to the network due to a blocked port. Which protocol is likely affected if port 68 is not open?

A. POP3

B. DNS

C. LDAP

D. DHCP

When clients are unable to connect to the network due to a blocked port, understanding which protocol operates over specific ports is crucial for diagnosing the issue. Port 68 is used by the Dynamic Host Configuration Protocol (DHCP) for client communication.

DHCP enables devices on a network to automatically obtain IP addresses and other network configuration parameters, which are vital for clients to connect successfully to the network. When a client sends a DHCP request, it uses port 68 to receive the DHCP offers from a server, which typically communicates with clients through port 67. If port 68 is blocked, clients won't be able to receive the necessary DHCP messages, resulting in failure to connect to the network.

In contrast, the other protocols listed, such as POP3, DNS, and LDAP, use different ports (110 for POP3, 53 for DNS, and 389 for LDAP) and would not be directly impacted by the blockage of port 68. Therefore, the likelihood of DHCP being affected by a blocked port 68 is high, making it the correct answer.