Fw: Add IP address to server

[meimi]

Hello,
  My provider assigned some IPs to my server. It is a FreeBSD 4.7 web
server. How should I add them all to my server?

  I have searched the handbook and found out that I only need to add this
line to /etc/rc.conf :
  ifconfig_fxp0_alias0="inet xxx.xxx.xxx.xxx netmask xxx.xxx.xxx.xxx"
Am I correct?
  However, I am not sure how to calculate netmask. The page I have read is
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/configtuning-virtu
al-hosts.html

Thanks
meimi