When Windows refuses to respect hosts file modifications, it typically indicates one of several configuration or system-level issues. Let's examine common scenarios with concrete examples:

# Example of a standard hosts file entry that SHOULD work
192.168.1.100    mylocalserver.dev

Windows aggressively caches DNS resolutions. Always flush after changes:

ipconfig /flushdns
ipconfig /registerdns
nbtstat -R
nbtstat -RR

Common formatting mistakes that break hosts files:

• UTF-8 with BOM encoding (should be ANSI or UTF-8 without BOM)
• Incorrect line endings (CRLF required)
• Comments (#) on the same line as entries

# Bad format example (will fail)
192.168.1.100    mylocalserver.dev # Local dev server

# Correct format
192.168.1.100    mylocalserver.dev
# Local dev server comment on separate line

Modern Windows versions require elevated permissions:

# PowerShell command to verify effective permissions
Get-Acl $env:windir\system32\drivers\etc\hosts | Format-List

The actual path should be:

C:\Windows\System32\drivers\etc\hosts

Check for these service dependencies:

sc query dnscache
sc query Dnscache | find "STATE"

For IPv6-enabled systems, add both IPv4 and IPv6 entries:

192.168.1.100    mylocalserver.dev
fe80::1%1        mylocalserver.dev

Enterprise environments often enforce DNS policies:

gpresult /h gpresult.html

For legacy systems still using NetBIOS names:

nbtstat -n

Essential diagnostic commands:

nslookup mylocalserver.dev
ping -a 192.168.1.100
tracert mylocalserver.dev

For persistent issues, create a test batch file:

@echo off
echo Testing hosts file resolution
ping mylocalserver.dev
nslookup mylocalserver.dev
pause

Verify these registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

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The Windows hosts file (%SystemRoot%\System32\drivers\etc\hosts) is a local DNS override mechanism that maps hostnames to IP addresses. When properly configured, it takes precedence over external DNS resolution.

• Incorrect file format (missing newline at EOF, wrong encoding)
• DNS caching issues (both Windows and browser caches)
• Incorrect file permissions (requires admin rights for modification)
• Group Policy restrictions
• Antivirus/security software interference
• IPv6 vs IPv4 resolution conflicts

First, verify basic functionality with this PowerShell command:

Test-NetConnection example.com -InformationLevel Detailed | Select-Object ComputerName, RemoteAddress

If the returned IP doesn't match your hosts entry, proceed with these checks:

Ensure your hosts file follows these technical requirements:

# Valid hosts file entry format
192.168.1.100    example.com    # comment
192.168.1.100    www.example.com

# Common mistakes to avoid:
192.168.1.100 example.com # missing tab
192.168.1.100example.com # no separator
::1    localhost # IPv6 entry might interfere

Execute these commands in sequence:

ipconfig /flushdns
nbtstat -R
nbtstat -RR

For persistent issues, use Process Monitor to track DNS queries:

# Filter for DNS query events
procmon.exe /AcceptEula /Quiet /Filter "Operation contains DNS"

Check for Group Policy restrictions with:

gpresult /H gpresult.html

Test name resolution priority with this PowerShell script:

$hostsEntry = "192.168.1.100 example.com"
[System.Net.Dns]::GetHostAddresses("example.com") | Select-Object IPAddressToString

Temporarily disable these features in your security software:

• DNS protection
• Network inspection
• Hosts file protection

Verify these registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\DNSClient

Use nslookup in interactive mode to bypass the cache:

nslookup
> set type=A
> example.com

For developers, test with raw sockets:

import socket
print(socket.gethostbyname('example.com'))

After making changes, verify with:

ping example.com
tracert example.com

Remember that some applications (like Chrome) may implement their own DNS cache. Use chrome://net-internals/#dns to clear it.