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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.

Network237.87.0.0/17
Usable hosts32,766
Subnet mask255.255.128.0
Addresses32,768
Network address
237.87.0.0
Broadcast address
237.87.127.255
First usable
237.87.0.1
Last usable
237.87.127.254
Usable hosts
32,766 (32,768 less the network and broadcast addresses)
Subnet mask
255.255.128.0
Wildcard mask
0.0.127.255 (Cisco ACLs, OSPF)
Prefix length
/17
Type
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex ED570000 · Integer 3981901824 to 3981934591
Reverse DNS zones
0.87.237.in-addr.arpa
1.87.237.in-addr.arpa
2.87.237.in-addr.arpa
3.87.237.in-addr.arpa
4.87.237.in-addr.arpa
5.87.237.in-addr.arpa
6.87.237.in-addr.arpa
7.87.237.in-addr.arpa
8.87.237.in-addr.arpa
9.87.237.in-addr.arpa
10.87.237.in-addr.arpa
11.87.237.in-addr.arpa
12.87.237.in-addr.arpa
13.87.237.in-addr.arpa
14.87.237.in-addr.arpa
15.87.237.in-addr.arpa
and 112 more
/17 is not on a 8-bit boundary, so it takes 128 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11101101.01010111.00000000.00000000237.87.0.0
Subnet mask11111111.11111111.10000000.00000000255.255.128.0
Network11101101.01010111.00000000.00000000237.87.0.0
Broadcast11101101.01010111.01111111.11111111237.87.127.255
Split into smaller subnets/24
/18 (2)/19 (4)/20 (8)/21 (16)/22 (32)/23 (64)/24 (128)/25 (256)/26 (512)/27 (1,024)/28 (2,048)/29 (4,096)

237.87.0.0/17 makes 128 subnets of /24.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1237.87.0.0/24237.87.0.1 to 237.87.0.254237.87.0.255254
2237.87.1.0/24237.87.1.1 to 237.87.1.254237.87.1.255254
3237.87.2.0/24237.87.2.1 to 237.87.2.254237.87.2.255254
4237.87.3.0/24237.87.3.1 to 237.87.3.254237.87.3.255254
5237.87.4.0/24237.87.4.1 to 237.87.4.254237.87.4.255254
6237.87.5.0/24237.87.5.1 to 237.87.5.254237.87.5.255254
7237.87.6.0/24237.87.6.1 to 237.87.6.254237.87.6.255254
8237.87.7.0/24237.87.7.1 to 237.87.7.254237.87.7.255254
9237.87.8.0/24237.87.8.1 to 237.87.8.254237.87.8.255254
10237.87.9.0/24237.87.9.1 to 237.87.9.254237.87.9.255254
11237.87.10.0/24237.87.10.1 to 237.87.10.254237.87.10.255254
12237.87.11.0/24237.87.11.1 to 237.87.11.254237.87.11.255254
13237.87.12.0/24237.87.12.1 to 237.87.12.254237.87.12.255254
14237.87.13.0/24237.87.13.1 to 237.87.13.254237.87.13.255254
15237.87.14.0/24237.87.14.1 to 237.87.14.254237.87.14.255254
16237.87.15.0/24237.87.15.1 to 237.87.15.254237.87.15.255254
17237.87.16.0/24237.87.16.1 to 237.87.16.254237.87.16.255254
18237.87.17.0/24237.87.17.1 to 237.87.17.254237.87.17.255254
19237.87.18.0/24237.87.18.1 to 237.87.18.254237.87.18.255254
20237.87.19.0/24237.87.19.1 to 237.87.19.254237.87.19.255254
21237.87.20.0/24237.87.20.1 to 237.87.20.254237.87.20.255254
22237.87.21.0/24237.87.21.1 to 237.87.21.254237.87.21.255254
23237.87.22.0/24237.87.22.1 to 237.87.22.254237.87.22.255254
24237.87.23.0/24237.87.23.1 to 237.87.23.254237.87.23.255254
25237.87.24.0/24237.87.24.1 to 237.87.24.254237.87.24.255254
26237.87.25.0/24237.87.25.1 to 237.87.25.254237.87.25.255254
27237.87.26.0/24237.87.26.1 to 237.87.26.254237.87.26.255254
28237.87.27.0/24237.87.27.1 to 237.87.27.254237.87.27.255254
29237.87.28.0/24237.87.28.1 to 237.87.28.254237.87.28.255254
30237.87.29.0/24237.87.29.1 to 237.87.29.254237.87.29.255254
31237.87.30.0/24237.87.30.1 to 237.87.30.254237.87.30.255254
32237.87.31.0/24237.87.31.1 to 237.87.31.254237.87.31.255254
33237.87.32.0/24237.87.32.1 to 237.87.32.254237.87.32.255254
34237.87.33.0/24237.87.33.1 to 237.87.33.254237.87.33.255254
35237.87.34.0/24237.87.34.1 to 237.87.34.254237.87.34.255254
36237.87.35.0/24237.87.35.1 to 237.87.35.254237.87.35.255254
37237.87.36.0/24237.87.36.1 to 237.87.36.254237.87.36.255254
38237.87.37.0/24237.87.37.1 to 237.87.37.254237.87.37.255254
39237.87.38.0/24237.87.38.1 to 237.87.38.254237.87.38.255254
40237.87.39.0/24237.87.39.1 to 237.87.39.254237.87.39.255254
41237.87.40.0/24237.87.40.1 to 237.87.40.254237.87.40.255254
42237.87.41.0/24237.87.41.1 to 237.87.41.254237.87.41.255254
43237.87.42.0/24237.87.42.1 to 237.87.42.254237.87.42.255254
44237.87.43.0/24237.87.43.1 to 237.87.43.254237.87.43.255254
45237.87.44.0/24237.87.44.1 to 237.87.44.254237.87.44.255254
46237.87.45.0/24237.87.45.1 to 237.87.45.254237.87.45.255254
47237.87.46.0/24237.87.46.1 to 237.87.46.254237.87.46.255254
48237.87.47.0/24237.87.47.1 to 237.87.47.254237.87.47.255254
49237.87.48.0/24237.87.48.1 to 237.87.48.254237.87.48.255254
50237.87.49.0/24237.87.49.1 to 237.87.49.254237.87.49.255254
51237.87.50.0/24237.87.50.1 to 237.87.50.254237.87.50.255254
52237.87.51.0/24237.87.51.1 to 237.87.51.254237.87.51.255254
53237.87.52.0/24237.87.52.1 to 237.87.52.254237.87.52.255254
54237.87.53.0/24237.87.53.1 to 237.87.53.254237.87.53.255254
55237.87.54.0/24237.87.54.1 to 237.87.54.254237.87.54.255254
56237.87.55.0/24237.87.55.1 to 237.87.55.254237.87.55.255254
57237.87.56.0/24237.87.56.1 to 237.87.56.254237.87.56.255254
58237.87.57.0/24237.87.57.1 to 237.87.57.254237.87.57.255254
59237.87.58.0/24237.87.58.1 to 237.87.58.254237.87.58.255254
60237.87.59.0/24237.87.59.1 to 237.87.59.254237.87.59.255254
61237.87.60.0/24237.87.60.1 to 237.87.60.254237.87.60.255254
62237.87.61.0/24237.87.61.1 to 237.87.61.254237.87.61.255254
63237.87.62.0/24237.87.62.1 to 237.87.62.254237.87.62.255254
64237.87.63.0/24237.87.63.1 to 237.87.63.254237.87.63.255254
65237.87.64.0/24237.87.64.1 to 237.87.64.254237.87.64.255254
66237.87.65.0/24237.87.65.1 to 237.87.65.254237.87.65.255254
67237.87.66.0/24237.87.66.1 to 237.87.66.254237.87.66.255254
68237.87.67.0/24237.87.67.1 to 237.87.67.254237.87.67.255254
69237.87.68.0/24237.87.68.1 to 237.87.68.254237.87.68.255254
70237.87.69.0/24237.87.69.1 to 237.87.69.254237.87.69.255254
71237.87.70.0/24237.87.70.1 to 237.87.70.254237.87.70.255254
72237.87.71.0/24237.87.71.1 to 237.87.71.254237.87.71.255254
73237.87.72.0/24237.87.72.1 to 237.87.72.254237.87.72.255254
74237.87.73.0/24237.87.73.1 to 237.87.73.254237.87.73.255254
75237.87.74.0/24237.87.74.1 to 237.87.74.254237.87.74.255254
76237.87.75.0/24237.87.75.1 to 237.87.75.254237.87.75.255254
77237.87.76.0/24237.87.76.1 to 237.87.76.254237.87.76.255254
78237.87.77.0/24237.87.77.1 to 237.87.77.254237.87.77.255254
79237.87.78.0/24237.87.78.1 to 237.87.78.254237.87.78.255254
80237.87.79.0/24237.87.79.1 to 237.87.79.254237.87.79.255254
81237.87.80.0/24237.87.80.1 to 237.87.80.254237.87.80.255254
82237.87.81.0/24237.87.81.1 to 237.87.81.254237.87.81.255254
83237.87.82.0/24237.87.82.1 to 237.87.82.254237.87.82.255254
84237.87.83.0/24237.87.83.1 to 237.87.83.254237.87.83.255254
85237.87.84.0/24237.87.84.1 to 237.87.84.254237.87.84.255254
86237.87.85.0/24237.87.85.1 to 237.87.85.254237.87.85.255254
87237.87.86.0/24237.87.86.1 to 237.87.86.254237.87.86.255254
88237.87.87.0/24237.87.87.1 to 237.87.87.254237.87.87.255254
89237.87.88.0/24237.87.88.1 to 237.87.88.254237.87.88.255254
90237.87.89.0/24237.87.89.1 to 237.87.89.254237.87.89.255254
91237.87.90.0/24237.87.90.1 to 237.87.90.254237.87.90.255254
92237.87.91.0/24237.87.91.1 to 237.87.91.254237.87.91.255254
93237.87.92.0/24237.87.92.1 to 237.87.92.254237.87.92.255254
94237.87.93.0/24237.87.93.1 to 237.87.93.254237.87.93.255254
95237.87.94.0/24237.87.94.1 to 237.87.94.254237.87.94.255254
96237.87.95.0/24237.87.95.1 to 237.87.95.254237.87.95.255254
97237.87.96.0/24237.87.96.1 to 237.87.96.254237.87.96.255254
98237.87.97.0/24237.87.97.1 to 237.87.97.254237.87.97.255254
99237.87.98.0/24237.87.98.1 to 237.87.98.254237.87.98.255254
100237.87.99.0/24237.87.99.1 to 237.87.99.254237.87.99.255254
101237.87.100.0/24237.87.100.1 to 237.87.100.254237.87.100.255254
102237.87.101.0/24237.87.101.1 to 237.87.101.254237.87.101.255254
103237.87.102.0/24237.87.102.1 to 237.87.102.254237.87.102.255254
104237.87.103.0/24237.87.103.1 to 237.87.103.254237.87.103.255254
105237.87.104.0/24237.87.104.1 to 237.87.104.254237.87.104.255254
106237.87.105.0/24237.87.105.1 to 237.87.105.254237.87.105.255254
107237.87.106.0/24237.87.106.1 to 237.87.106.254237.87.106.255254
108237.87.107.0/24237.87.107.1 to 237.87.107.254237.87.107.255254
109237.87.108.0/24237.87.108.1 to 237.87.108.254237.87.108.255254
110237.87.109.0/24237.87.109.1 to 237.87.109.254237.87.109.255254
111237.87.110.0/24237.87.110.1 to 237.87.110.254237.87.110.255254
112237.87.111.0/24237.87.111.1 to 237.87.111.254237.87.111.255254
113237.87.112.0/24237.87.112.1 to 237.87.112.254237.87.112.255254
114237.87.113.0/24237.87.113.1 to 237.87.113.254237.87.113.255254
115237.87.114.0/24237.87.114.1 to 237.87.114.254237.87.114.255254
116237.87.115.0/24237.87.115.1 to 237.87.115.254237.87.115.255254
117237.87.116.0/24237.87.116.1 to 237.87.116.254237.87.116.255254
118237.87.117.0/24237.87.117.1 to 237.87.117.254237.87.117.255254
119237.87.118.0/24237.87.118.1 to 237.87.118.254237.87.118.255254
120237.87.119.0/24237.87.119.1 to 237.87.119.254237.87.119.255254
121237.87.120.0/24237.87.120.1 to 237.87.120.254237.87.120.255254
122237.87.121.0/24237.87.121.1 to 237.87.121.254237.87.121.255254
123237.87.122.0/24237.87.122.1 to 237.87.122.254237.87.122.255254
124237.87.123.0/24237.87.123.1 to 237.87.123.254237.87.123.255254
125237.87.124.0/24237.87.124.1 to 237.87.124.254237.87.124.255254
126237.87.125.0/24237.87.125.1 to 237.87.125.254237.87.125.255254
127237.87.126.0/24237.87.126.1 to 237.87.126.254237.87.126.255254
128237.87.127.0/24237.87.127.1 to 237.87.127.254237.87.127.255254

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.