RFC 1860
Variable Length Subnet Table For IPv4
RFC 1860: Variable Length Subnet Table For IPv4 🎀
okay bestie, this is RFC 1860 ✨ and it is pure subnet-mask lore 💅 It's an Informational doc from October 1995, written by T. Pummill (Alantec) and B. Manning (ISI) 🦋 It came out of the Network Working Group, and it doesn't obsolete or update anything, since the title block has no Obsoletes or Updates line 🌸
Status of this Memo 🌈
this memo is here to give info to the Internet community 💖 It does not specify an Internet standard of any kind, and distribution of it is unlimited ✨
Abstract 🧚
this doc itemizes the potential values for IPv4 subnets 🫶 You also get extra info on Hex and Decimal values, classful equivalents, and how many addresses are available in each block. Huge thanks to Bruce Pinsky (cisco) and Daniel Karrenberg (RIPE) for their inputs 🍓
Table 🦋
this table lists the variable length subnets from 1 to 32, with the CIDR form and the Decimal equivalents next to them. It's giving reference chart energy and I'm obsessed 😭
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
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 routeExamples 💅
these tables show some ways to split the subnet and host bits inside a couple of 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 2From 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 💀
okay so the memo says security issues are not discussed in this memo 🙈 No security talk here, so keep your own security hat on when you use these tables 👑
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📦 where this page comes from
- ietf: rfc1860 1995-10
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms