200-201 Question 116
Single answerA network administrator has configured a router to use PAT (Port Address Translation) for internal devices accessing the internet. When investigating an issue, the administrator observes that multiple internal devices are successfully sharing the same public IP address to connect to different external services. However, one device is unable to establish a connection to an external web server. What is the most likely cause of this issue?
- A
The NAT table on the router has exceeded its maximum number of entries.
- B
The public IP address used for PAT is not mapped to the internal device.
- C
The external web server does not support incoming connections from translated IP addresses.
- D
The internal device is not configured with the correct default gateway.
Show answer and explanation
Correct answer: A
Explanation
PAT (Port Address Translation) allows multiple devices to share a single public IP address by using unique port numbers for each connection. However, the NAT table on the router has a finite size, and if it becomes full, new connections cannot be established. This is the most likely cause of the issue described in the scenario.
- A. Correct.
Correct. PAT relies on a NAT table to track connections. If the NAT table is full, new connections cannot be established, which could prevent the internal device from connecting to the web server.
- B. Incorrect.
Incorrect. In PAT, all internal devices share a single public IP address. The issue is unlikely to be caused by a lack of mapping of the public IP to the internal device.
- C. Incorrect.
Incorrect. Most external web servers are designed to handle connections from translated IP addresses. This is not a common cause of connection issues in a PAT setup.
- D. Incorrect.
Incorrect. If the internal device did not have the correct default gateway, it would likely be unable to reach any external resources, not just a specific web server.