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Network Working Group T. Pummill
Request for Comments: 1860 Alantec
Category: Informational B. Manning
ISI
October 1995
Variable Length Subnet Table For IPv4
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
Abstract
This document itemizes the potential values for IPv4 subnets.
Additional information is provided for Hex and Decmial values,
classfull equivalents, and number of addresses available within the
indicated block. We appreciate inputs from Bruce Pinsky (cisco) and
Daniel Karrenberg (RIPE).
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. Security Considerations Security issues are not discussed in this memo. Authors' Addresses Troy Pummill EMail: trop@alantec.com Bill Manning Information Sciences Institute University of Southern California 4676 Admiralty Way Marina del Rey, CA 90292-6695 USA Phone: +1 310-822-1511 x387 Fax: +1 310-823-6714 EMail: bmanning@isi.edu Pummill & Manning Informational [Page 3]