Guidance for macOS Network Tuning

This page provides tuning recommendations for macOS hosts connected at speeds of 1Gbps or higher. These settings are designed to enhance network performance for high-speed connections. Do not apply these settings on laptops primarily using Wi-Fi connections or on systems connected at speeds of 100 Mbps or lower, as they may degrade performance.

Self-Tuning TCP in Modern macOS Versions

Starting with macOS 10.5, Apple implemented "self-tuning TCP," which dynamically adjusts certain parameters to optimize performance. While defaults have improved over time, adjustments are still necessary to fully utilize high-speed connections.

Default Settings in Recent macOS Versions

Recent macOS versions come with the following defaults (values may vary slightly depending on the exact version):

• net.inet.tcp.win_scale_factor: 3
• net.inet.tcp.autorcvbufmax: 4MB 
• net.inet.tcp.autosndbufmax: 4MB

Suggested Settings for High-Speed Connections

To optimize performance on 1Gbps or faster networks, increase the TCP window scaling factor and autotuning buffer maximums. Add the following settings to the /etc/sysctl.conf file (or apply them dynamically using sysctl commands):

# Increase TCP window scaling factor (default is 3-6; increase to 8)
net.inet.tcp.win_scale_factor=8

# Increase maximum receive buffer for TCP autotuning to 32MB
net.inet.tcp.autorcvbufmax=33554432

# Increase maximum send buffer for TCP autotuning to 32MB
net.inet.tcp.autosndbufmax=33554432
    

Applying the Changes

1. Create or edit the sysctl configuration file:

   sudo nano /etc/sysctl.conf

   Add the settings above to the file.
2. Apply changes immediately (without rebooting):

   sudo sysctl -w net.inet.tcp.win_scale_factor=8
   sudo sysctl -w net.inet.tcp.autorcvbufmax=33554432
   sudo sysctl -w net.inet.tcp.autosndbufmax=33554432
               

3. Make the changes persistent: Ensure /etc/sysctl.conf is loaded at boot by creating a LaunchDaemon or using a boot script if the file isn't loaded automatically in modern macOS versions.
4. Verify the settings: Use the following command to check the current values:

   sysctl net.inet.tcp

Notes for macOS Ventura and Later

macOS Ventura and later versions use System Integrity Protection (SIP) to restrict changes to system files. If /etc/sysctl.conf is not recognized, consider applying settings dynamically via scripts or using alternative methods like creating a plist in /Library/LaunchDaemons.

Additional Considerations

• These settings are ideal for high-performance use cases, such as file servers, high-throughput applications, or research environments.
• Revert settings if they cause instability or reduced performance for your specific use case.