RFC 1860 Subnet Table October 1995 FF.FF.E0.00 /19 255.255.224.0 8 K 32 C FF.FF.F0.00 /20 255.255.240.0 4 K 16 C FF.FF.F8.00 /21 255.255.248.0 2 K 8 C FF.FF.FC.00 /22 255.255.252.0 1 K 4 C FF.FF.FE.00 /23 255.255.254.0 512 2 C FF.FF.FF.00 /24 255.255.255.0 256 1 C FF.FF.FF.80 /25 255.255.255.128 128 FF.FF.FF.C0 /26 255.255.255.192 64 FF.FF.FF.E0 /27 255.255.255.224 32 FF.FF.FF.F0 /28 255.255.255.240 16 FF.FF.FF.F8 /29 255.255.255.248 8 FF.FF.FF.FC /30 255.255.255.252 4 FF.FF.FF.FE /31 255.255.255.254 This space is not usable FF.FF.FF.FF /32 255.255.255.255 This is a single host route Examples The following tables illistrate some options for subnet/host partions within selected block sizes. From a /16 block # bits Mask Effective Subnets Effective Hosts ======== ===== ================= =============== 2 255.255.192.0 2 16382 3 255.255.224.0 6 8190 4 255.255.240.0 14 4094 5 255.255.248.0 30 2046 6 255.255.252.0 62 1022 7 255.255.254.0 126 510 8 255.255.255.0 254 254 9 255.255.255.128 510 126 10 255.255.255.192 1022 62 11 255.255.255.224 2046 30 12 255.255.255.240 4094 14 13 255.255.255.248 8190 6 14 255.255.255.252 16382 2 Pummill & Manning Informational