configure static permanent route on red hat or cent os

put it in the file in this case corresponding to eth0 inteface

file:
/etc/sysconfig/network-scripts/route-eth0

content:
GATEWAY0=192.168.1.254
NETMASK0=255.255.255.0
ADDRESS0=192.168.99.0

meaning:
all the traffic to addreses 192.168.99.* go through gateway 192.168.1.254

equivalent temporal route command:
route add -net 192.168.99.0/24 gw 192.168.1.254