Cannot access particular IPs family

Hi,

I've experienced a strange behaviour of my CentoOS dedicated server...
When I try to WGET some web page the system timeout like it cannot
estabilish connection due some firewall restrictions.
Note that I can WGET a wide range of internet page but only a few are
unreachable!!

I've found that this bug come out when the IP of the web page is in a
particular subset (63.x.x.x for example).

Obviously the same bug causes crash of my PHP procedure when I use fopen or 
fsocket...


Any idea?


Thank you