PHP's IP management functions and binary arithmetic functions are seriously broken (see bug report logged) Due to this limitation, the biggest subnet that can be created is limited to 254k hosts.
This brokenness also prevents the use of the ip2long() and long2ip() functions introduced with php 4.x. I have used php only functions called inet_aton() and inet_ntoa().
SNMP appears to be broken on Redhat 7.2 systems. Try following these instructions for help.