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RFC 1860

                 Variable Length Subnet Table For IPv4

Table

   The following table lists the variable length subnets from 1 to 32,
   the CIDR representation form and the Decmial equivalents.

   Mask value:
   Hex            CIDR   Decimal           #of add    Classfull
   80.00.00.00    /1     128.0.0.0         2048 M     128 A
   C0.00.00.00    /2     192.0.0.0         1024 M      64 A
   E0.00.00.00    /3     224.0.0.0          512 M      32 A
   F0.00.00.00    /4     240.0.0.0          256 M      16 A
   F8.00.00.00    /5     248.0.0.0          128 M       8 A
   FC.00.00.00    /6     252.0.0.0           64 M       4 A
   FE.00.00.00    /7     254.0.0.0           32 M       2 A
   FF.00.00.00    /8     255.0.0.0           16 M       1 A
   FF.80.00.00    /9     255.128.0.0          8 M     128 B
   FF.C0.00.00   /10     255.192.0.0          4 M      64 B
   FF.E0.00.00   /11     255.224.0.0          2 M      32 B
   FF.F0.00.00   /12     255.240.0.0       1024 K      16 B
   FF.F8.00.00   /13     255.248.0.0        512 K       8 B
   FF.FC.00.00   /14     255.252.0.0        256 K       4 B
   FF.FE.00.00   /15     255.254.0.0        128 K       2 B
   FF.FF.00.00   /16     255.255.0.0         64 K       1 B
   FF.FF.80.00   /17     255.255.128.0       32 K     128 C
   FF.FF.C0.00   /18     255.255.192.0       16 K      64 C



Pummill & Manning            Informational                      [Page 1]

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 [Page 2]
RFC 1860 Subnet Table October 1995 From a /24 block # bits Mask Effective Subnets Effective Hosts ======== ===== ================= =============== 2 255.255.255.192 2 62 3 255.255.255.224 6 30 4 255.255.255.240 14 14 5 255.255.255.248 30 6 6 255.255.255.252 62 2 *Subnet all zeroes and all ones excluded. *Host all zeroes and all ones excluded. References [1] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless Inter- Domain Routing (CIDR): an Address Assignment and Aggregation Strategy", RFC 1519, BARRNet, cicso, Merit, OARnet, September 1993



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