Optional NOT operator of ports problem

[An Tran]

Hi all, 

I was having a problem with the optional NOT operator of ports. I have tested this rule but it didn't worked: 

#ipfw add xxx allow ip from xx.xx.xx.xx to any not 25 
ipfw: unknown argument ``not'' 

My server is running FreeBSD 4.9-STABLE and I have seen in the ipfw man page that we can use the optional not operator as follow:
...
src and dst: {addr | { addr or ... }} [[not] ports] 
An address (or a list, see below) optionally followed by ports 
specifiers. 
...
ports: {port | port-port}[,ports]
For protocols which support port numbers (such as TCP and UDP),
optional ports may be specified as one or more ports or port
ranges, separated by commas but no spaces, and an optional not
operator. The `-' notation specifies a range of ports (including
boundaries).
...

 
Could anyone please tell me that what was wrong in my rule?
 
Thank you in advance.





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