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Network Working Group Request for Comments: 1860 Category: Informational

T. Pummill Alantec 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 80.00.00.00 C0.00.00.00 E0.00.00.00 F0.00.00.00 F8.00.00.00 FC.00.00.00 FE.00.00.00 FF.00.00.00 FF.80.00.00 FF.C0.00.00 FF.E0.00.00 FF.F0.00.00 FF.F8.00.00 FF.FC.00.00 FF.FE.00.00 FF.FF.00.00 FF.FF.80.00 FF.FF.C0.00

CIDR /1 /2 /3 /4 /5 /6 /7 /8 /9 /10 /11 /12 /13 /14 /15 /16 /17 /18

Decimal 128.0.0.0 192.0.0.0 224.0.0.0 240.0.0.0 248.0.0.0 252.0.0.0 254.0.0.0 255.0.0.0 255.128.0.0 255.192.0.0 255.224.0.0 255.240.0.0 255.248.0.0 255.252.0.0 255.254.0.0 255.255.0.0 255.255.128.0 255.255.192.0

#of 2048 1024 512 256 128 64 32 16 8 4 2 1024 512 256 128 64 32 16

add M M M M M M M M M M M K K K K K K K

Classfull 128 A 64 A 32 A 16 A 8A 4A 2A 1A 128 B 64 B 32 B 16 B 8B 4B 2B 1B 128 C 64 C

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RFC 1860

Subnet Table

October 1995

FF.FF.E0.00 FF.FF.F0.00 FF.FF.F8.00 FF.FF.FC.00 FF.FF.FE.00 FF.FF.FF.00 FF.FF.FF.80 FF.FF.FF.C0 FF.FF.FF.E0 FF.FF.FF.F0 FF.FF.FF.F8 FF.FF.FF.FC FF.FF.FF.FE FF.FF.FF.FF Examples

/19 /20 /21 /22 /23 /24 /25 /26 /27 /28 /29 /30 /31 /32

255.255.224.0 255.255.240.0 255.255.248.0 255.255.252.0 255.255.254.0 255.255.255.0 255.255.255.128 255.255.255.192 255.255.255.224 255.255.255.240 255.255.255.248 255.255.255.252 255.255.255.254 255.255.255.255

8 4 2 1 512 256 128 64 32 16 8 4 This This

K K K K

32 16 8 4 2 1

C C C C C C

space is not usable is a single host route

The following tables illistrate some options for subnet/host partions within selected block sizes. From a /16 block # bits ======== 2 3 4 5 6 7 8 9 10 11 12 13 14 Mask ===== 255.255.192.0 255.255.224.0 255.255.240.0 255.255.248.0 255.255.252.0 255.255.254.0 255.255.255.0 255.255.255.128 255.255.255.192 255.255.255.224 255.255.255.240 255.255.255.248 255.255.255.252 Effective Subnets ================= 2 6 14 30 62 126 254 510 1022 2046 4094 8190 16382 Effective Hosts =============== 16382 8190 4094 2046 1022 510 254 126 62 30 14 6 2

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RFC 1860

Subnet Table

October 1995

From a /24 block # bits ======== 2 3 4 5 6 Mask ===== 255.255.255.192 255.255.255.224 255.255.255.240 255.255.255.248 255.255.255.252 Effective Subnets ================= 2 6 14 30 62 Effective Hosts =============== 62 30 14 6 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 InterDomain 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

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