A SOHO user cannot connect to the internet. Their configuration shows: IP: 192.168.223.15 Mask: 255.255.255.0 Gateway: 192.168.233.1 DNS: 8.8.8.8, 4.2.2.1, 4.2.2.2 Baseline documentation shows valid subnet range: 192.168.200.0–192.168.232.255. Which setting must be changed?

For a device to communicate with the internet, its default gateway must be on the same logical subnet. The user's computer has an IP address of 192.168.223.15 and a subnet mask of 255.255.255.0. This configuration places the computer on the 192.168.223.0/24 network. However, the configured gateway is 192.168.233.1, which is on a completely different subnet (192.168.233.0/24). Because the gateway is not on the same local network, the computer cannot send traffic to it, thus preventing any access to the internet. The gateway setting must be changed to an address within the 192.168.223.x range (e.g., 192.168.223.1).

A. Tertiary DNS: The DNS servers are valid public resolvers; the issue is with routing at the IP layer, not name resolution.
B. Secondary DNS: Same as the tertiary DNS, this is not the source of the routing problem.
C. Primary DNS: Same as the other DNS options, the configured server (8.8.8.8) is correct and reachable if routing were working.
D. IP Address: While the IP could be changed, the gateway is definitively on the wrong subnet relative to the IP, making the gateway the incorrect setting.
F. Subnet mask: The /24 mask is standard for this IP class. Altering it to an unconventional mask is less likely than a simple typo in the gateway address.

1. Microsoft. (2021, March 31). Core network guide. Microsoft Learn. "For TCP/IP to work correctly, you need to configure each computer with... an IP address, a subnet mask, and a default gateway." It further explains these components must be logically consistent.

2. Comer, D. E. (2018). Computer Networks and Internets (6th ed.). Pearson. Chapter 19, "Internet Addressing," explains the principle that a host's IP address and its default router's (gateway's) IP address must share the same network prefix as defined by the subnet mask.

3. Massachusetts Institute of Technology (MIT). (n.d.). IP Address, Subnet Mask, and Default Gateway for a Wireless Connection in Windows 10. MIT Information Systems & Technology Knowledge Base, Article 66331. "The Default Gateway is the IP address of the router that connects your network to the Internet... It must be on the same subnet as your computer's IP address."