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IP subnet calculator

Type an address with its prefix or mask to see the network, its usable range and masks. Split it into smaller subnets, or look up any prefix in the reference tables.

Network237.2.112.0/21
Usable hosts2,046
Subnet mask255.255.248.0
Addresses2,048
Network address
237.2.112.0
Broadcast address
237.2.119.255
First usable
237.2.112.1
Last usable
237.2.119.254
Usable hosts
2,046 (2,048 less the network and broadcast addresses)
Subnet mask
255.255.248.0
Wildcard mask
0.0.7.255 (Cisco ACLs, OSPF)
Prefix length
/21
Type
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex ED027000 · Integer 3976359936 to 3976361983
Reverse DNS zones
112.2.237.in-addr.arpa
113.2.237.in-addr.arpa
114.2.237.in-addr.arpa
115.2.237.in-addr.arpa
116.2.237.in-addr.arpa
117.2.237.in-addr.arpa
118.2.237.in-addr.arpa
119.2.237.in-addr.arpa
/21 is not on a 8-bit boundary, so it takes 8 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11101101.00000010.01110000.00000000237.2.112.0
Subnet mask11111111.11111111.11111000.00000000255.255.248.0
Network11101101.00000010.01110000.00000000237.2.112.0
Broadcast11101101.00000010.01110111.11111111237.2.119.255
Split into smaller subnets/27
/22 (2)/23 (4)/24 (8)/25 (16)/26 (32)/27 (64)/28 (128)/29 (256)/30 (512)/31 (1,024)/32 (2,048)

237.2.112.0/21 makes 64 subnets of /27.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1237.2.112.0/27237.2.112.1 to 237.2.112.30237.2.112.3130
2237.2.112.32/27237.2.112.33 to 237.2.112.62237.2.112.6330
3237.2.112.64/27237.2.112.65 to 237.2.112.94237.2.112.9530
4237.2.112.96/27237.2.112.97 to 237.2.112.126237.2.112.12730
5237.2.112.128/27237.2.112.129 to 237.2.112.158237.2.112.15930
6237.2.112.160/27237.2.112.161 to 237.2.112.190237.2.112.19130
7237.2.112.192/27237.2.112.193 to 237.2.112.222237.2.112.22330
8237.2.112.224/27237.2.112.225 to 237.2.112.254237.2.112.25530
9237.2.113.0/27237.2.113.1 to 237.2.113.30237.2.113.3130
10237.2.113.32/27237.2.113.33 to 237.2.113.62237.2.113.6330
11237.2.113.64/27237.2.113.65 to 237.2.113.94237.2.113.9530
12237.2.113.96/27237.2.113.97 to 237.2.113.126237.2.113.12730
13237.2.113.128/27237.2.113.129 to 237.2.113.158237.2.113.15930
14237.2.113.160/27237.2.113.161 to 237.2.113.190237.2.113.19130
15237.2.113.192/27237.2.113.193 to 237.2.113.222237.2.113.22330
16237.2.113.224/27237.2.113.225 to 237.2.113.254237.2.113.25530
17237.2.114.0/27237.2.114.1 to 237.2.114.30237.2.114.3130
18237.2.114.32/27237.2.114.33 to 237.2.114.62237.2.114.6330
19237.2.114.64/27237.2.114.65 to 237.2.114.94237.2.114.9530
20237.2.114.96/27237.2.114.97 to 237.2.114.126237.2.114.12730
21237.2.114.128/27237.2.114.129 to 237.2.114.158237.2.114.15930
22237.2.114.160/27237.2.114.161 to 237.2.114.190237.2.114.19130
23237.2.114.192/27237.2.114.193 to 237.2.114.222237.2.114.22330
24237.2.114.224/27237.2.114.225 to 237.2.114.254237.2.114.25530
25237.2.115.0/27237.2.115.1 to 237.2.115.30237.2.115.3130
26237.2.115.32/27237.2.115.33 to 237.2.115.62237.2.115.6330
27237.2.115.64/27237.2.115.65 to 237.2.115.94237.2.115.9530
28237.2.115.96/27237.2.115.97 to 237.2.115.126237.2.115.12730
29237.2.115.128/27237.2.115.129 to 237.2.115.158237.2.115.15930
30237.2.115.160/27237.2.115.161 to 237.2.115.190237.2.115.19130
31237.2.115.192/27237.2.115.193 to 237.2.115.222237.2.115.22330
32237.2.115.224/27237.2.115.225 to 237.2.115.254237.2.115.25530
33237.2.116.0/27237.2.116.1 to 237.2.116.30237.2.116.3130
34237.2.116.32/27237.2.116.33 to 237.2.116.62237.2.116.6330
35237.2.116.64/27237.2.116.65 to 237.2.116.94237.2.116.9530
36237.2.116.96/27237.2.116.97 to 237.2.116.126237.2.116.12730
37237.2.116.128/27237.2.116.129 to 237.2.116.158237.2.116.15930
38237.2.116.160/27237.2.116.161 to 237.2.116.190237.2.116.19130
39237.2.116.192/27237.2.116.193 to 237.2.116.222237.2.116.22330
40237.2.116.224/27237.2.116.225 to 237.2.116.254237.2.116.25530
41237.2.117.0/27237.2.117.1 to 237.2.117.30237.2.117.3130
42237.2.117.32/27237.2.117.33 to 237.2.117.62237.2.117.6330
43237.2.117.64/27237.2.117.65 to 237.2.117.94237.2.117.9530
44237.2.117.96/27237.2.117.97 to 237.2.117.126237.2.117.12730
45237.2.117.128/27237.2.117.129 to 237.2.117.158237.2.117.15930
46237.2.117.160/27237.2.117.161 to 237.2.117.190237.2.117.19130
47237.2.117.192/27237.2.117.193 to 237.2.117.222237.2.117.22330
48237.2.117.224/27237.2.117.225 to 237.2.117.254237.2.117.25530
49237.2.118.0/27237.2.118.1 to 237.2.118.30237.2.118.3130
50237.2.118.32/27237.2.118.33 to 237.2.118.62237.2.118.6330
51237.2.118.64/27237.2.118.65 to 237.2.118.94237.2.118.9530
52237.2.118.96/27237.2.118.97 to 237.2.118.126237.2.118.12730
53237.2.118.128/27237.2.118.129 to 237.2.118.158237.2.118.15930
54237.2.118.160/27237.2.118.161 to 237.2.118.190237.2.118.19130
55237.2.118.192/27237.2.118.193 to 237.2.118.222237.2.118.22330
56237.2.118.224/27237.2.118.225 to 237.2.118.254237.2.118.25530
57237.2.119.0/27237.2.119.1 to 237.2.119.30237.2.119.3130
58237.2.119.32/27237.2.119.33 to 237.2.119.62237.2.119.6330
59237.2.119.64/27237.2.119.65 to 237.2.119.94237.2.119.9530
60237.2.119.96/27237.2.119.97 to 237.2.119.126237.2.119.12730
61237.2.119.128/27237.2.119.129 to 237.2.119.158237.2.119.15930
62237.2.119.160/27237.2.119.161 to 237.2.119.190237.2.119.19130
63237.2.119.192/27237.2.119.193 to 237.2.119.222237.2.119.22330
64237.2.119.224/27237.2.119.225 to 237.2.119.254237.2.119.25530

IPv4 CIDR reference (/0 to /32)

IPv4 prefix lengths
PrefixSubnet maskWildcardAddressesUsable hostsSizeTypical use
/00.0.0.0255.255.255.2554,294,967,2964,294,967,29416,777,216 × /24
/1128.0.0.0127.255.255.2552,147,483,6482,147,483,6468,388,608 × /24
/2192.0.0.063.255.255.2551,073,741,8241,073,741,8224,194,304 × /24
/3224.0.0.031.255.255.255536,870,912536,870,9102,097,152 × /24
/4240.0.0.015.255.255.255268,435,456268,435,4541,048,576 × /24
/5248.0.0.07.255.255.255134,217,728134,217,726524,288 × /24
/6252.0.0.03.255.255.25567,108,86467,108,862262,144 × /24
/7254.0.0.01.255.255.25533,554,43233,554,430131,072 × /24
/8255.0.0.00.255.255.25516,777,21616,777,21465,536 × /24Old class A; 10.0.0.0/8
/9255.128.0.00.127.255.2558,388,6088,388,60632,768 × /24
/10255.192.0.00.63.255.2554,194,3044,194,30216,384 × /24
/11255.224.0.00.31.255.2552,097,1522,097,1508,192 × /24
/12255.240.0.00.15.255.2551,048,5761,048,5744,096 × /24172.16.0.0/12
/13255.248.0.00.7.255.255524,288524,2862,048 × /24
/14255.252.0.00.3.255.255262,144262,1421,024 × /24
/15255.254.0.00.1.255.255131,072131,070512 × /24
/16255.255.0.00.0.255.25565,53665,534256 × /24Old class B; 192.168.0.0/16
/17255.255.128.00.0.127.25532,76832,766128 × /24
/18255.255.192.00.0.63.25516,38416,38264 × /24
/19255.255.224.00.0.31.2558,1928,19032 × /24
/20255.255.240.00.0.15.2554,0964,09416 × /24
/21255.255.248.00.0.7.2552,0482,0468 × /24
/22255.255.252.00.0.3.2551,0241,0224 × /24Large office or guest Wi-Fi (1,022 hosts)
/23255.255.254.00.0.1.2555125102 × /24Larger office LAN (510 hosts)
/24255.255.255.00.0.0.2552562541 × /24Typical office LAN (old class C)
/25255.255.255.1280.0.0.1271281261/2 of a /24Smaller LAN or VLAN
/26255.255.255.1920.0.0.6364621/4 of a /24Smaller LAN or VLAN
/27255.255.255.2240.0.0.3132301/8 of a /24Small VLAN, phones, cameras
/28255.255.255.2400.0.0.1516141/16 of a /24Small VLAN, phones, cameras
/29255.255.255.2480.0.0.7861/32 of a /24Small fixed public block (5 usable)
/30255.255.255.2520.0.0.3421/64 of a /24Point-to-point (old style)
/31255.255.255.2540.0.0.1221/128 of a /24Point-to-point link (RFC 3021)
/32255.255.255.2550.0.0.0111/256 of a /24One host

IPv6 prefix reference

IPv6 prefix lengths
PrefixAddresses/64 LANs/48 sitesNibbleTypical use
/342,535,295,865,117,307,932,921,825,928,971,026,432 (2^125)2,305,843,009,213,693,95235,184,372,088,832NoAll global unicast (2000::/3)
/165,192,296,858,534,827,628,530,496,329,220,096 (2^112)281,474,976,710,6564,294,967,296Yes
/20324,518,553,658,426,726,783,156,020,576,256 (2^108)17,592,186,044,416268,435,456YesLarge provider allocation (RIPE minimum for some)
/29633,825,300,114,114,700,748,351,602,688 (2^99)34,359,738,368524,288NoRIPE allocation to a provider (often)
/3279,228,162,514,264,337,593,543,950,336 (2^96)4,294,967,29665,536YesProvider allocation (RIPE default)
/364,951,760,157,141,521,099,596,496,896 (2^92)268,435,4564,096Yes
/40309,485,009,821,345,068,724,781,056 (2^88)16,777,216256Yes
/4419,342,813,113,834,066,795,298,816 (2^84)1,048,57616Yes
/481,208,925,819,614,629,174,706,176 (2^80)65,5361YesOne site or organisation (RIPE PI / assignment)
/5275,557,863,725,914,323,419,136 (2^76)4,096Yes
/564,722,366,482,869,645,213,696 (2^72)256YesSmall site or home (common provider assignment)
/60295,147,905,179,352,825,856 (2^68)16YesSome home broadband (16 LANs)
/6418,446,744,073,709,551,616 (2^64)1YesOne LAN or VLAN (needed for SLAAC)
/7272,057,594,037,927,936 (2^56)1/256 of a /64Yes
/80281,474,976,710,656 (2^48)1/65,536 of a /64Yes
/964,294,967,2961/4,294,967,296 of a /64YesEmbeds an IPv4 address (NAT64)
/11265,5361/281,474,976,710,656 of a /64Yes
/1202561/72,057,594,037,927,936 of a /64Yes
/124161/1,152,921,504,606,846,976 of a /64Yes
/12641/4,611,686,018,427,387,904 of a /64No
/12721/9,223,372,036,854,775,808 of a /64NoPoint-to-point link (RFC 6164)
/12811/18,446,744,073,709,551,616 of a /64YesOne host or loopback

Private and special ranges

IPv4

Special-purpose ranges
RangeNameWhat it is
255.255.255.255/32Limited broadcastEvery host on the local network
0.0.0.0/8This networkNot routed; 0.0.0.0 means "any address" in settings
10.0.0.0/8Private (RFC 1918)Office and home networks; not routed on the internet
100.64.0.0/10Shared address space (CGNAT)Used by providers behind carrier-grade NAT (RFC 6598)
127.0.0.0/8LoopbackThis computer
169.254.0.0/16Link-local (APIPA)Self-assigned when no DHCP server answers
172.16.0.0/12Private (RFC 1918)Office and home networks; not routed on the internet
192.0.0.0/24IETF protocol assignmentsSpecial uses such as DS-Lite
192.0.2.0/24Documentation (TEST-NET-1)For examples; never used on a network
192.88.99.0/246to4 relay (deprecated)Formerly anycast for 6to4
192.168.0.0/16Private (RFC 1918)Office and home networks; not routed on the internet
198.18.0.0/15BenchmarkingNetwork equipment testing (RFC 2544)
198.51.100.0/24Documentation (TEST-NET-2)For examples; never used on a network
203.0.113.0/24Documentation (TEST-NET-3)For examples; never used on a network
224.0.0.0/4MulticastOne-to-many traffic, such as IPTV and routing protocols
240.0.0.0/4ReservedFuture use; not usable on most systems

IPv6

Special-purpose ranges
RangeNameWhat it is
::/128UnspecifiedNo address; :: means "any address" in settings
::1/128LoopbackThis computer
::ffff:0:0/96IPv4-mappedAn IPv4 address written as IPv6
64:ff9b::/96NAT64IPv4 addresses reached through a NAT64 gateway
100::/64Discard onlyTraffic sent here is dropped (RFC 6666)
2001:db8::/32DocumentationFor examples; never used on a network
2001::/32TeredoIPv6 tunnelled over IPv4 UDP
2002::/166to4IPv6 tunnelled over IPv4 (largely retired)
3fff::/20DocumentationFor examples (RFC 9637)
fc00::/7Unique local (ULA)Private IPv6, like RFC 1918; usually fd00::/8
fe80::/10Link-localEvery IPv6 interface has one; not routed
ff00::/8MulticastOne-to-many traffic; replaces broadcast
2000::/3Global unicastPublic internet addresses

About this tool

A network is written as an address and a prefix length, such as 192.168.1.0/24: the first 24 bits name the network and the rest number the devices on it. The calculator works out where the network starts and ends, how many devices it holds, its subnet and wildcard masks, and the reverse DNS zone to ask your provider for.

It also splits a network into equal smaller ones (one per VLAN or site), turns a range of addresses into the fewest CIDR blocks for a firewall rule, and lists every IPv4 prefix length and the common IPv6 ones in reference tables.

Common questions

Why are two addresses lost in every IPv4 subnet?

The first address names the network and the last is the broadcast address, so a /24 has 256 addresses but 254 for devices. A /31 (a link between two routers) and a /32 (one host) are the exceptions.

What size of IPv6 network should a LAN use?

Always /64. Devices pick their own address within it (SLAAC), which needs the full 64 bits. A site usually gets a /48 or /56 from its provider, which holds 65,536 or 256 LANs.

What is a wildcard mask?

The subnet mask turned inside out: 255.255.255.0 becomes 0.0.0.255. Cisco access lists and OSPF use it to say which bits must match.

Which ranges can I use inside an office?

IPv4: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. IPv6: unique local addresses from fd00::/8, though most networks use the public prefix from their provider.