Overview
This lecture explains the purpose, function, and continued relevance of host files in computer networking, particularly before and alongside DNS technology.
Host Files: Purpose and Function
- Host files map human-friendly names to network addresses in a simple text format.
- Each line in a host file contains an IP address followed by a hostname (e.g., "1.2.3.4 webserver").
- The operating system’s networking stack uses the host file to resolve hostnames to IP addresses.
- Host file entries allow users to type names instead of IP addresses in applications and commands.
- Host files predate DNS and were an early solution for hostname resolution.
Loopback Address and Host Files
- The loopback address refers to the local machine, sending traffic to itself.
- IPv4 uses 127.0.0.1 as the loopback address; IPv6 uses ::1 (colon colon one).
- Hosts files almost always include mappings like "127.0.0.1 localhost" and "::1 localhost".
- Traffic directed to a loopback address never leaves the computer's own networking stack.
Current Use and Security Considerations
- Hosts files are still present in all major operating systems despite widespread DNS use.
- Some software relies on specific host file entries for proper operation.
- Malicious software may alter host files to redirect or disrupt network traffic.
- Host files are useful for troubleshooting and can override DNS for individual computers.
- The system checks the host file before attempting DNS resolution.
Key Terms & Definitions
- Host File — A plain text file mapping hostnames to IP addresses, used by the OS for name resolution.
- Loopback Address — An IP address that routes network traffic back to the local machine (127.0.0.1 for IPv4, ::1 for IPv6).
- DNS (Domain Name System) — A global system for translating human-friendly domain names into IP addresses.
Action Items / Next Steps
- Review host file format and common entries (e.g., 127.0.0.1 localhost).
- Understand when and why to use host files for troubleshooting network issues.