How to disable SMB 1 or NetBIOS in macOS

Learn how to disable SMB 1 or NetBIOS to prevent failover.

This article is intended for enterprise and education system administrators.

SMB 1 and NetBIOS are enabled by default in macOS to improve compatibility with third-party products. macOS will attempt to use the later versions of SMB, as well as DNS and port 445, with failover to port 139 and SMB 1 as needed. You can disable SMB 1 or NetBIOS to prevent this failover.

To disable SMB 1, add the following line to the /etc/nsmb.conf file:

protocol_vers_map=6

To disable NetBIOS, add the following line to the /etc/nsmb.conf file:

port445=no_netbios

The /etc/nsmb.conf file doesn't exist by default. To create one and apply both of the above changes, use the following Terminal commands:

echo "[default]" | sudo tee -a /etc/nsmb.conf
echo "protocol_vers_map=6" | sudo tee -a /etc/nsmb.conf
echo "port445=no_netbios" | sudo tee -a /etc/nsmb.conf

To revert the above changes, you can delete the /etc/nsmb.conf file safely.

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