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TL;DR: If
localhost or 127.0.0.1 stopped working after a Windows 11 update, fix it in this order:
- Verify the app is actually listening on 127.0.0.1 or ::1 and the expected port.
- Reset winsock/DNS, clear NRPT and proxies, and re-add loopback exemptions for Store apps.
- Repair the
hostsfile, re-enablelocalhostmapping, and flush caches. - Check Windows Defender Firewall rules (private/public) and disable conflicting port proxies/VPN DNS hijacks.
- For WSL/Hyper-V/IIS Express, rebind to the correct interface or recreate dev-certs and URLACLs.
Audience: US • EU • UK • AU • IN developers, SRE/DevOps, AppSec, and IT helpdesks dealing with broken local dev servers after Patch Tuesday.
Symptoms You’ll See
ERR_CONNECTION_REFUSED,Hmmm… can’t reach this page, orcurl: (7) Failed to connecttolocalhost.ping localhostresolves to IPv6::1but your app only listens on127.0.0.1(or vice-versa).- Port suddenly “in use” by a different PID after update (IIS Express or a security agent grabbing :80/:443).
- Only UWP/Store apps (Edge WebView2, Teams, Mail) can’t hit
localhostdue to loopback isolation.
Step 1 — Confirm Something Is Actually Listening
# PowerShell (run as Administrator) Get-NetTCPConnection -State Listen | Sort-Object -Property LocalPort | Select-Object -First 30 ` | Format-Table LocalAddress,LocalPort,OwningProcess # Classic netstat -ano | findstr LISTENING # Map PID → process tasklist /fi "PID eq <PID>"
If your app is bound to 0.0.0.0:3000 it should accept localhost:3000. If it’s bound only to 192.168.x.x, update the bind address to 127.0.0.1 or add a second listener.
Step 2 — Quick Health Resets (Safe, Reversible)
# Run in elevated PowerShell ipconfig /flushdns netsh winsock reset netsh int ip reset # Remove stale Name Resolution Policy Table (NRPT) entries that can hijack localhost Get-DnsClientNrptRule | Remove-DnsClientNrptRule -Force # Disable system-wide proxy if accidentally enabled by VPN/update netsh winhttp show proxy netsh winhttp reset proxy
Step 3 — Repair the hosts File
Updates or security tools sometimes comment out localhost. Ensure these lines exist (and aren’t duplicated):
# C:\Windows\System32\drivers\etc\hosts (edit as Administrator) 127.0.0.1 localhost ::1 localhost
Step 4 — Re-enable Loopback for Store/UWP Apps
Windows app container isolation can block WebView/Store apps (e.g., Edge WebView2, Teams) from hitting localhost. Exempt your app package family name (PFN) or exempt all for dev boxes:
# List packages to find PFN PowerShell> Get-AppxPackage | Select Name, PackageFamilyName # Exempt a specific PFN CheckNetIsolation LoopbackExempt -a -n=Microsoft.WindowsTerminal_8wekyb3d8bbwe # As last resort during active development (review later!) CheckNetIsolation LoopbackExempt -a -p=all # Verify CheckNetIsolation LoopbackExempt -s
Step 5 — Fix Windows Defender Firewall & Profile Mismatch
- Updates can flip your network to Public. Your inbound rule may be Private-only.
- Create (or edit) an allow rule for your port on both Private and Public while you test.
# Example: open 3000 TCP on both profiles (dev only; remove when done) New-NetFirewallRule -DisplayName "Dev-Local-3000" -Direction Inbound -Protocol TCP -LocalPort 3000 -Action Allow -Profile Private,Public
Step 6 — Kill Conflicting Port Proxies & Services
Some VPNs or prior IIS/HTTP.SYS config leave port proxies behind.
# Show any portproxy rules (remove unexpected ones) netsh interface portproxy show all netsh interface portproxy reset # IIS/HTTP.SYS URL reservations (for self-hosted Kestrel, etc.) netsh http show urlacl # Example: remove a stale reservation netsh http delete urlacl url=http://+:3000/
Also check common “hijackers”: security agents, Docker Desktop, WSLg, IIS Express. If :80/:443 are taken by System (PID 4), HTTP.SYS is bound—use a different port or adjust URLACLs.
Step 7 — WSL / Hyper-V / IIS Express Specifics
- WSL: If you hit
localhostfrom Windows to a WSL service, ensure the app binds to0.0.0.0in Linux or expose viawsl.exe --shutdownthen restart. Recreate dev certs if you serve HTTPS from WSL. - Hyper-V/Dev VMs: NAT switch changes post-update; confirm port-forward rules in
Get-NetNatStaticMapping. - IIS Express: Rebuild
applicationhost.config, or re-create dev certs:dotnet dev-certs https --clean dotnet dev-certs https --trust
Step 8 — IPv4 vs IPv6 Preference (Temporary Toggle)
If your app only listens on IPv4 and Windows prefers IPv6 ::1 for localhost, either bind dual-stack or temporarily prefer IPv4:
# Prefer IPv4 over IPv6 (requires reboot) — TEMPORARY on dev boxes only reg add "HKLM\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters" /v DisabledComponents /t REG_DWORD /d 0x20 /f
Revert later by deleting DisabledComponents or setting to 0.
Step 9 — Clean Browser/Cert State
- Clear HSTS for
localhost(Chrome:chrome://net-internals/#hsts) if you toggled HTTP/HTTPS. - Ensure trusted dev certificate is present (
certmgr.msc→ Trusted Root Certification Authorities). - Test with
curl -v http://127.0.0.1:PORTandcurl -v http://localhost:PORT(compare DNS/SSL behavior).
One-Click Script (Paste into Elevated PowerShell)
Review before running. This performs safe resets, restores hosts, clears NRPT/proxy, and prints listeners.
$hosts = "$env:SystemRoot\System32\drivers\etc\hosts"
$bk = "$hosts.bak.$((Get-Date).ToString('yyyyMMddHHmmss'))"
Copy-Item $hosts $bk -Force
# Ensure localhost mappings exist exactly once
$lines = Get-Content $hosts | Where-Object {$_ -notmatch '^\s*#'}
$ipv4 = '127.0.0.1 localhost'
$ipv6 = '::1 localhost'
$filtered = ($lines | Where-Object {$_ -notmatch '\slocalhost(\s|$)'} )
$filtered += $ipv4, $ipv6
$filtered | Set-Content -Path $hosts -Encoding ASCII
ipconfig /flushdns | Out-Null
netsh winsock reset | Out-Null
netsh int ip reset | Out-Null
if (Get-Command Get-DnsClientNrptRule -ErrorAction SilentlyContinue) {
Get-DnsClientNrptRule | Remove-DnsClientNrptRule -Force 2>$null
}
netsh winhttp reset proxy | Out-Null
Write-Host "`nActive listeners:" -ForegroundColor Cyan
Get-NetTCPConnection -State Listen | Sort-Object LocalPort | ft -AutoSize LocalAddress,LocalPort,OwningProcess
Still Broken? Quick Triage Matrix
| Symptom | Likely Cause | Fix |
|---|---|---|
| Only Store apps can’t reach localhost | Loopback isolation | CheckNetIsolation LoopbackExempt -a -p=all (dev) or per-PFN |
| Ping localhost resolves to ::1 but app listens on 127.0.0.1 | IPv6 preference mismatch | Bind dual-stack or temporarily prefer IPv4 |
| Port in use by PID 4 (System) | HTTP.SYS URL reservation | netsh http show urlacl and delete or change app port |
| Works after VPN disconnect | VPN NRPT/proxy rewrite | Reset NRPT/proxy; add split-tunnel exceptions |
Random ECONNREFUSED spikes |
AV/EDR HTTPS inspection or port hijack | Exclude dev ports/certs; restart agent or change ports |
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Why trust CyberDudeBivash? We publish vendor-agnostic, executive-grade fixes and runbooks that help US/EU/UK/AU/IN teams restore services fast and reduce blast radius across developer workstations and enterprise fleets.
Windows 11, localhost, 127.0.0.1, ::1, winsock, NRPT, hosts file, firewall, URLACL, HTTP.SYS, IIS Express, WSL, Hyper-V, VPN, split tunnel, DevOps, SRE, AppSec, enterprise IT support.
#Windows11 #Localhost #Developers #DevOps #SRE #AppSec #WSL #IISExpress #Winsock #Firewall #VPN #NRPT #Loopback #Troubleshooting #EnterpriseIT #US #EU #UK #Australia #India
Educational and defensive guidance only. Validate commands in a non-production environment before applying to enterprise fleets.
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