FTP slow between files

I am running an FTP server (ncFTP on RedHat v7) behind a Linux firewall. I am also running DNS cache-only on the firewall as well as SSH.

The system works well with one small exception. When transferring a group of files, there is a long pause between files. I recall once reading that this was due to waiting for DNS to time out but what I don’t remember are the exact details or how to fix it.

I would really appreciate information on the fix (or further information on the cause for thisbehavior).

thanks!

paul