Adjusts various TCP and network settings in Windows to enhance the speed of the Internet connection.

README.md

Most of these settings were mentioned on SpeedGuide.net and MajorGeek.com.

Medium article

Optimize-TCPSettings.ps1

#Requires -RunAsAdministrator
<#
.SYNOPSIS
    Network performance optimization script for Windows 10/11.

.DESCRIPTION
    Applies TCP and network stack tweaks targeting lower latency.
    Skips settings that are read-only or no-ops on Windows 10/11 consumer editions.
    Run in an elevated PowerShell session.

.NOTES
    Test your connection before and after with a tool like ping, winMTR, or iPerf.
    A reboot is recommended after running this script.
#>

Set-StrictMode -Version Latest
$ErrorActionPreference = 'Stop'

function Write-Step {
    param([string]$Message)
    Write-Host "`n>> $Message" -ForegroundColor Cyan
}

function Write-Skip {
    param([string]$Message)
    Write-Host "   SKIPPED: $Message" -ForegroundColor DarkGray
}

# ---------------------------------------------
# SECTION 1 - TCP Global Settings (netsh)
# These apply on Windows 10/11 and have measurable effect.
# ---------------------------------------------

Write-Step "Setting congestion provider."
# CTCP (Compound TCP) can improve throughput on higher-latency links.
# Alternative: bbr2 is theoretically better but has known bugs on Windows
# and may break VPN/proxy tools. Stick with ctcp unless you want to experiment.
# To try BBR2: netsh int tcp set supplemental template=internet congestionprovider=bbr2
netsh int tcp set supplemental template=internet congestionprovider=ctcp | Out-Null

Write-Step "Disabling TCP timestamps."
# Reduces per-packet overhead. Minor latency benefit on LAN/low-latency links.
netsh int tcp set global timestamps=disabled | Out-Null

Write-Step "Setting initial Retransmission Timeout (RTO) to 300ms."
# Default is 1000ms. 300ms is the minimum and benefits low-latency connections
# by retrying faster on packet loss without waiting a full second.
netsh int tcp set global initialRto=300 | Out-Null

Write-Step "Disabling Receive Segment Coalescing (RSC) globally."
# RSC batches incoming segments to reduce CPU load, but adds latency.
# Disable for lower latency; re-enable if you prioritize throughput over latency.
netsh int tcp set global rsc=disabled | Out-Null

Write-Step "Enabling RSS and Direct Cache Access (DCA) globally."
# RSS (Receive-Side Scaling) spreads network processing across CPU cores.
# DCA (Direct Cache Access) can reduce memory latency - requires hardware support
# (Intel VT-d / DCA-capable NIC). Safe to enable; silently ignored if unsupported.
netsh int tcp set global rss=enabled dca=enabled | Out-Null

Write-Step "Disabling Non-SACK RTT Resiliency globally."
# Reduces unnecessary retransmits on modern networks where SACK is standard.
netsh int tcp set global nonsackrttresiliency=disabled | Out-Null

Write-Step "Setting maximum SYN retransmissions to 2."
# Default is 4. Reduces the time spent waiting for a response from a dead host.
netsh int tcp set global maxsynretransmissions=2 | Out-Null

# ---------------------------------------------
# SECTION 2 - Dynamic Port Range
# ---------------------------------------------

Write-Step "Setting dynamic port range (IPv4 and IPv6)."
# Expands the ephemeral port pool. Useful under heavy connection load.
# Start at 10000 with 55534 ports (up to 65534) for maximum range.
netsh int ipv4 set dynamicport tcp start=10000 num=55534 | Out-Null
netsh int ipv6 set dynamicport tcp start=10000 num=55534 | Out-Null

# ---------------------------------------------
# SECTION 3 - Network Adapter Offload Settings
# ---------------------------------------------

Write-Step "Disabling TCP Chimney Offload globally."
# TCP Chimney is deprecated and disabled by default in modern Windows.
# Explicitly disabling it ensures no legacy path activates it.
Set-NetOffloadGlobalSetting -Chimney Disabled | Out-Null

Write-Step "Enabling Checksum Offload on all network adapters."
# Offloads checksum computation to the NIC, reducing CPU overhead.
Enable-NetAdapterChecksumOffload -Name * -ErrorAction SilentlyContinue | Out-Null

Write-Step "Enabling Receive-Side Scaling (RSS) on all network adapters."
Enable-NetAdapterRss -Name * -ErrorAction SilentlyContinue | Out-Null

Write-Step "Disabling Receive Segment Coalescing (RSC) on all network adapters."
# Per-adapter RSC disable to match the global setting above.
Disable-NetAdapterRsc -Name * -ErrorAction SilentlyContinue | Out-Null

Write-Step "Disabling Large Send Offload (LSO) on all network adapters."
# LSO can introduce latency spikes by batching large sends. Disable for
# more consistent low-latency behavior. Re-enable if throughput suffers.
Disable-NetAdapterLso -Name * -ErrorAction SilentlyContinue | Out-Null

Write-Step "Disabling Packet Coalescing Filter globally."
Disable-NetAdapterPacketDirect -Name * -ErrorAction SilentlyContinue | Out-Null
Set-NetOffloadGlobalSetting -PacketCoalescingFilter Disabled | Out-Null

# ---------------------------------------------
# SECTION 4 - Registry: TCP/IP Parameters
# ---------------------------------------------

Write-Step "Setting TCP/IP registry parameters."

# Standard TTL of 64 (Linux/macOS default). Reduces unnecessary router hops
# before packet expiry. 128 is the Windows default - 64 is more RFC-standard.
reg add "HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters" /t REG_DWORD /v DefaultTTL /d 64 /f | Out-Null

# Maximizes the ephemeral port ceiling (65534 is the max valid port).
reg add "HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters" /t REG_DWORD /v MaxUserPort /d 65534 /f | Out-Null

# Reduces TIME_WAIT state from 240s default to 30s.
# Frees up ports faster after connections close. Safe for client machines.
reg add "HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters" /t REG_DWORD /v TcpTimedWaitDelay /d 30 /f | Out-Null

# ---------------------------------------------
# SECTION 5 - Registry: DNS Resolution Priority
# ---------------------------------------------

Write-Step "Setting DNS resolution priority order."
# Lower number = higher priority. This order: local hosts file first,
# then local (mDNS/NetBT), then DNS, then NetBT fallback.
# Speeds up local hostname resolution and reduces unnecessary DNS queries.
reg add "HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\ServiceProvider" /v "LocalPriority"  /t REG_DWORD /d 4 /f | Out-Null
reg add "HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\ServiceProvider" /v "HostsPriority"  /t REG_DWORD /d 5 /f | Out-Null
reg add "HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\ServiceProvider" /v "DnsPriority"    /t REG_DWORD /d 6 /f | Out-Null
reg add "HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\ServiceProvider" /v "NetbtPriority"  /t REG_DWORD /d 7 /f | Out-Null

# ---------------------------------------------
# DONE
# ---------------------------------------------

Write-Host "`n---------------------------------------------" -ForegroundColor Green
Write-Host "  Network optimization complete. Reboot recommended." -ForegroundColor Green
Write-Host "---------------------------------------------" -ForegroundColor Green
Write-Host ""
Write-Host "  To verify TCP global settings after reboot:" -ForegroundColor Yellow
Write-Host "    netsh int tcp show global" -ForegroundColor White
Write-Host ""
Write-Host "  To revert congestion provider to Windows default (Cubic):" -ForegroundColor Yellow
Write-Host "    netsh int tcp set supplemental template=internet congestionprovider=default" -ForegroundColor White
Write-Host ""

The three Set-NetTCPSetting is useless unless you are using winserver. See https://learn.microsoft.com/en-us/powershell/module/nettcpip/set-nettcpsetting?view=windowsserver2025-ps#description Besides your value is the default value on my win11.

Personally I think none of these options are valid under normal internet connection.

If you are optimizing for low latency network (rather than high bandwidth), I think these may help (no guarantee):

netsh int tcp set global initialRto=300
netsh int tcp set global timestamps=disabled
netsh int tcp set global rsc=disabled 

dca=enabled: may be useful. But its status doesn't show up in my netsh int tcp show global. AI says it needs hardware support.

netsh int tcp set supplemental template=internet congestionprovider=bbr2: theoretically better than cubic both on internet and home LAN. But the windows implementation has been buggy, which may cause network worse. Have a try. If not good, switch to cubic (default on win11). I have tested that it's not compatible with my proxy tool.

@imba-tjd thanks for the info. You are correct, it's useless on Windows 10/11.

I've updated the script with several changes, including adding the commands you mentioned which should help.