u-allow-multiple-logins-per-username-only-if-same-ip NcFTPd general.cf file configuration
Don't forget to restart NcFTPd after modifying the general.cf file.

This long-winded option's name is self-explanatory.  Set it to yes if you have a situation where you want to allow more than one login to accounts but only if the IP address is the same as the first login to the account.  By default, users can login to the same account from different addresses.

Examples:

Recommendation:

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