dhcp server dropping external ip

after so many hours the dhcp server just drops the external ip and i am unable to ping outside of network. ive read up on the leases part of the dhcp configuration but not exactly sure if that is my problem or not, is there anything i need to check as to why the connection to the outside world is being dropped randomly?

here is my dhcpd.conf file

subnet 192.168.1.0 netmask 255.255.255.0 {
       option routers  192.168.1.100;
       option subnet-mask      255.255.255.0;

       option domain-name "nc.rr.com";
       option domain-name-servers 24.25.4.109;

       option time-offset -18000;

       host server1 {
               option host-name "server1.servbox.com";
               hardware ethernet 00:08:A1:73:E8:44;
               fixed-address 192.168.1.100;
       }

       host flea {
               option host-name "flea.servbox.com";
               hardware ethernet 00:60:08:C7:84:69;
               fixed-address 192.168.1.10;
       }

}

thanks
adam