Troubleshooting Connection Problem: TCP Port 80 | CCNA Exam Answer

Troubleshooting Connection Problem: TCP Port 80

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While troubleshooting a connection problem on a computer, you determined that the computer can ping a specific web server but it cannot connect to TCP port 80 on that server. Which reason for the problem is most likely true?



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A. B. C. D.


The most likely reason for the problem is D. An ACL (Access Control List) is blocking the TCP port.


Ping is a utility that sends an ICMP (Internet Control Message Protocol) echo request to a target host, and waits for an ICMP echo reply. It's used to test if a network host is reachable and responding. Ping works at the network layer (Layer 3) of the OSI model.

TCP (Transmission Control Protocol) is a protocol that provides reliable, ordered, and error-checked delivery of data between applications. TCP works at the transport layer (Layer 4) of the OSI model.

Port 80 is the default port for HTTP (Hypertext Transfer Protocol) which is used for web browsing. When a client (such as a web browser) connects to a web server, it opens a TCP connection to the server's port 80, and sends an HTTP request to retrieve a web page.

If the computer can ping the web server but cannot connect to TCP port 80, it means that the network connectivity is fine, but something is blocking the connection on port 80.

VLANs (Virtual Local Area Networks) are used to partition a physical network into multiple logical segments. ARP (Address Resolution Protocol) is used to map a network address (such as an IP address) to a physical address (such as a MAC address). Routes are used to determine the path that network traffic takes from one network to another.

None of these issues would cause a specific port (such as TCP port 80) to be blocked. The most likely cause is an ACL that is configured to block traffic to TCP port 80. An ACL is a set of rules that is used to filter traffic based on source and destination addresses, protocols, ports, and other criteria.

Therefore, option D is the correct answer.