Which component is used to resolve domain names locally without contacting DNS servers?

• A. The hosts file, a local text file mapping domain names to IP addresses.
• B. The DHCP server on the network.
• C. The router's NAT table.
• D. The browser's bookmarks file.

Answer: (A)

Local name resolution can be done using a dedicated, system-wide mapping that the operating system checks before querying any external DNS servers. The hosts file is exactly that: a plain text database that pairs domain names with IP addresses. When a program asks for the IP of a domain, the resolver first looks in this file; if it finds a matching entry, it returns the associated IP without reaching out to DNS servers. This happens because the hosts file is consulted locally by the OS’s resolver, making the lookup entirely self-contained.

Where you find it depends on the OS. On Windows, it’s at C:\Windows\System32\drivers\etc\hosts; on Linux and macOS, it’s /etc/hosts. The format is simple: each line has an IP address followed by one or more hostnames, with comments starting with #. This mechanism is handy for testing, blocking sites by mapping them to 127.0.0.1, or overriding DNS for specific domains. However, it requires manual updates and is not scalable for large networks, and if there’s no entry there, the system will proceed to use normal DNS. Other choices like DHCP, NAT tables, or a browser’s bookmarks file do not provide local domain-to-IP resolution in the same way.