opening ports

hello,

maybe a simple and not interesting question *** how do i open port 20 and 21 for my SBS server?

i had SP1 on my server *** updated it with SP2, now if i want to FTP i don`t have a connection. i think the port is blocked. when i look at the routing and ras i see FTP so does it mean it already is open?

i did not change anything on my modem because it workt before installing SP2..

can anyone help me?

regards stefan .