Preventing FTP Access with ACL

Can anyone please help - came across this question . .

How would you prevent FTP access to a host using only port numbers?

Would you have to code the following for both port numbers 20 and 21 or would just one of the FTP port numbers suffice?

access-list 101 deny tcp 172.16.00 0.0.255.255 any eq 20
access-list 101 deny tcp 172.16.00 0.0.255.255 any eq 21
access-list 101 permit ip any any

interface serial 0
ip access-group 101 in

Hope this makes sense - Many thanks

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Comments

mbeaven

I believe it's only necessary to block port 21 the control port since it's needed to establish the session. I don't have a router in front of me right now but I thought blocking port 21 is the same as putting eq ftp and shows that way in the config. I'm sure if I'm wrong someone will let me know about it.

mercanedees

Thank you mbeaven for the reply

wildfire

access-list 101 deny tcp 172.16.00 0.0.255.255 any eq ftp

this command blocks both port 20 and 21. However be carefull as people can use fpt through http passive mode which will use port 80 http for ftp access.

wildfire

forgot to say theres also secure ftp

access-list 110 deny tcp any any eq 115