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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.

Network237.65.76.0/23
Usable hosts510
Subnet mask255.255.254.0
Addresses512
Network address
237.65.76.0
Broadcast address
237.65.77.255
First usable
237.65.76.1
Last usable
237.65.77.254
Usable hosts
510 (512 less the network and broadcast addresses)
Subnet mask
255.255.254.0
Wildcard mask
0.0.1.255 (Cisco ACLs, OSPF)
Prefix length
/23
Type
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex ED414C00 · Integer 3980479488 to 3980479999
Reverse DNS zones
76.65.237.in-addr.arpa
77.65.237.in-addr.arpa
/23 is not on a 8-bit boundary, so it takes 2 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11101101.01000001.01001100.00000000237.65.76.0
Subnet mask11111111.11111111.11111110.00000000255.255.254.0
Network11101101.01000001.01001100.00000000237.65.76.0
Broadcast11101101.01000001.01001101.11111111237.65.77.255
Split into smaller subnets/29
/24 (2)/25 (4)/26 (8)/27 (16)/28 (32)/29 (64)/30 (128)/31 (256)/32 (512)

237.65.76.0/23 makes 64 subnets of /29.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1237.65.76.0/29237.65.76.1 to 237.65.76.6237.65.76.76
2237.65.76.8/29237.65.76.9 to 237.65.76.14237.65.76.156
3237.65.76.16/29237.65.76.17 to 237.65.76.22237.65.76.236
4237.65.76.24/29237.65.76.25 to 237.65.76.30237.65.76.316
5237.65.76.32/29237.65.76.33 to 237.65.76.38237.65.76.396
6237.65.76.40/29237.65.76.41 to 237.65.76.46237.65.76.476
7237.65.76.48/29237.65.76.49 to 237.65.76.54237.65.76.556
8237.65.76.56/29237.65.76.57 to 237.65.76.62237.65.76.636
9237.65.76.64/29237.65.76.65 to 237.65.76.70237.65.76.716
10237.65.76.72/29237.65.76.73 to 237.65.76.78237.65.76.796
11237.65.76.80/29237.65.76.81 to 237.65.76.86237.65.76.876
12237.65.76.88/29237.65.76.89 to 237.65.76.94237.65.76.956
13237.65.76.96/29237.65.76.97 to 237.65.76.102237.65.76.1036
14237.65.76.104/29237.65.76.105 to 237.65.76.110237.65.76.1116
15237.65.76.112/29237.65.76.113 to 237.65.76.118237.65.76.1196
16237.65.76.120/29237.65.76.121 to 237.65.76.126237.65.76.1276
17237.65.76.128/29237.65.76.129 to 237.65.76.134237.65.76.1356
18237.65.76.136/29237.65.76.137 to 237.65.76.142237.65.76.1436
19237.65.76.144/29237.65.76.145 to 237.65.76.150237.65.76.1516
20237.65.76.152/29237.65.76.153 to 237.65.76.158237.65.76.1596
21237.65.76.160/29237.65.76.161 to 237.65.76.166237.65.76.1676
22237.65.76.168/29237.65.76.169 to 237.65.76.174237.65.76.1756
23237.65.76.176/29237.65.76.177 to 237.65.76.182237.65.76.1836
24237.65.76.184/29237.65.76.185 to 237.65.76.190237.65.76.1916
25237.65.76.192/29237.65.76.193 to 237.65.76.198237.65.76.1996
26237.65.76.200/29237.65.76.201 to 237.65.76.206237.65.76.2076
27237.65.76.208/29237.65.76.209 to 237.65.76.214237.65.76.2156
28237.65.76.216/29237.65.76.217 to 237.65.76.222237.65.76.2236
29237.65.76.224/29237.65.76.225 to 237.65.76.230237.65.76.2316
30237.65.76.232/29237.65.76.233 to 237.65.76.238237.65.76.2396
31237.65.76.240/29237.65.76.241 to 237.65.76.246237.65.76.2476
32237.65.76.248/29237.65.76.249 to 237.65.76.254237.65.76.2556
33237.65.77.0/29237.65.77.1 to 237.65.77.6237.65.77.76
34237.65.77.8/29237.65.77.9 to 237.65.77.14237.65.77.156
35237.65.77.16/29237.65.77.17 to 237.65.77.22237.65.77.236
36237.65.77.24/29237.65.77.25 to 237.65.77.30237.65.77.316
37237.65.77.32/29237.65.77.33 to 237.65.77.38237.65.77.396
38237.65.77.40/29237.65.77.41 to 237.65.77.46237.65.77.476
39237.65.77.48/29237.65.77.49 to 237.65.77.54237.65.77.556
40237.65.77.56/29237.65.77.57 to 237.65.77.62237.65.77.636
41237.65.77.64/29237.65.77.65 to 237.65.77.70237.65.77.716
42237.65.77.72/29237.65.77.73 to 237.65.77.78237.65.77.796
43237.65.77.80/29237.65.77.81 to 237.65.77.86237.65.77.876
44237.65.77.88/29237.65.77.89 to 237.65.77.94237.65.77.956
45237.65.77.96/29237.65.77.97 to 237.65.77.102237.65.77.1036
46237.65.77.104/29237.65.77.105 to 237.65.77.110237.65.77.1116
47237.65.77.112/29237.65.77.113 to 237.65.77.118237.65.77.1196
48237.65.77.120/29237.65.77.121 to 237.65.77.126237.65.77.1276
49237.65.77.128/29237.65.77.129 to 237.65.77.134237.65.77.1356
50237.65.77.136/29237.65.77.137 to 237.65.77.142237.65.77.1436
51237.65.77.144/29237.65.77.145 to 237.65.77.150237.65.77.1516
52237.65.77.152/29237.65.77.153 to 237.65.77.158237.65.77.1596
53237.65.77.160/29237.65.77.161 to 237.65.77.166237.65.77.1676
54237.65.77.168/29237.65.77.169 to 237.65.77.174237.65.77.1756
55237.65.77.176/29237.65.77.177 to 237.65.77.182237.65.77.1836
56237.65.77.184/29237.65.77.185 to 237.65.77.190237.65.77.1916
57237.65.77.192/29237.65.77.193 to 237.65.77.198237.65.77.1996
58237.65.77.200/29237.65.77.201 to 237.65.77.206237.65.77.2076
59237.65.77.208/29237.65.77.209 to 237.65.77.214237.65.77.2156
60237.65.77.216/29237.65.77.217 to 237.65.77.222237.65.77.2236
61237.65.77.224/29237.65.77.225 to 237.65.77.230237.65.77.2316
62237.65.77.232/29237.65.77.233 to 237.65.77.238237.65.77.2396
63237.65.77.240/29237.65.77.241 to 237.65.77.246237.65.77.2476
64237.65.77.248/29237.65.77.249 to 237.65.77.254237.65.77.2556

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.