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rfc:rfc1860

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]

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