Configuration problem

[Gustavo Ritondale]

I have CDN access with 16 ip addresses. (subnet mask 255.255.255.240) I need a DMZ for servers and NAT for private LAN. I'll use ipchains firewall with 3 NICs.   Router = xxx.xxx.xxx.209   My question is: Should i divide ( split ) my 16 public addresses into 2 subnets ( with subnet mask=255.255.255.248) like         xxx.xxx.xxx.208 - xxx.xxx.xxx.215               xxx.xxx.xxx.216 - xxx.xxx.xxx.223 or i can leave subnet mask unchanged and install the firewall on xxx.xxx.xxx.210  ??   Thanks, GLR