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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.

Network237.2.128.0/19
Usable hosts8,190
Subnet mask255.255.224.0
Addresses8,192
Network address
237.2.128.0
Broadcast address
237.2.159.255
First usable
237.2.128.1
Last usable
237.2.159.254
Usable hosts
8,190 (8,192 less the network and broadcast addresses)
Subnet mask
255.255.224.0
Wildcard mask
0.0.31.255 (Cisco ACLs, OSPF)
Prefix length
/19
Type
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex ED028000 · Integer 3976364032 to 3976372223
Reverse DNS zones
128.2.237.in-addr.arpa
129.2.237.in-addr.arpa
130.2.237.in-addr.arpa
131.2.237.in-addr.arpa
132.2.237.in-addr.arpa
133.2.237.in-addr.arpa
134.2.237.in-addr.arpa
135.2.237.in-addr.arpa
136.2.237.in-addr.arpa
137.2.237.in-addr.arpa
138.2.237.in-addr.arpa
139.2.237.in-addr.arpa
140.2.237.in-addr.arpa
141.2.237.in-addr.arpa
142.2.237.in-addr.arpa
143.2.237.in-addr.arpa
and 16 more
/19 is not on a 8-bit boundary, so it takes 32 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11101101.00000010.10000000.00000000237.2.128.0
Subnet mask11111111.11111111.11100000.00000000255.255.224.0
Network11101101.00000010.10000000.00000000237.2.128.0
Broadcast11101101.00000010.10011111.11111111237.2.159.255
Split into smaller subnets/26
/20 (2)/21 (4)/22 (8)/23 (16)/24 (32)/25 (64)/26 (128)/27 (256)/28 (512)/29 (1,024)/30 (2,048)/31 (4,096)

237.2.128.0/19 makes 128 subnets of /26.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1237.2.128.0/26237.2.128.1 to 237.2.128.62237.2.128.6362
2237.2.128.64/26237.2.128.65 to 237.2.128.126237.2.128.12762
3237.2.128.128/26237.2.128.129 to 237.2.128.190237.2.128.19162
4237.2.128.192/26237.2.128.193 to 237.2.128.254237.2.128.25562
5237.2.129.0/26237.2.129.1 to 237.2.129.62237.2.129.6362
6237.2.129.64/26237.2.129.65 to 237.2.129.126237.2.129.12762
7237.2.129.128/26237.2.129.129 to 237.2.129.190237.2.129.19162
8237.2.129.192/26237.2.129.193 to 237.2.129.254237.2.129.25562
9237.2.130.0/26237.2.130.1 to 237.2.130.62237.2.130.6362
10237.2.130.64/26237.2.130.65 to 237.2.130.126237.2.130.12762
11237.2.130.128/26237.2.130.129 to 237.2.130.190237.2.130.19162
12237.2.130.192/26237.2.130.193 to 237.2.130.254237.2.130.25562
13237.2.131.0/26237.2.131.1 to 237.2.131.62237.2.131.6362
14237.2.131.64/26237.2.131.65 to 237.2.131.126237.2.131.12762
15237.2.131.128/26237.2.131.129 to 237.2.131.190237.2.131.19162
16237.2.131.192/26237.2.131.193 to 237.2.131.254237.2.131.25562
17237.2.132.0/26237.2.132.1 to 237.2.132.62237.2.132.6362
18237.2.132.64/26237.2.132.65 to 237.2.132.126237.2.132.12762
19237.2.132.128/26237.2.132.129 to 237.2.132.190237.2.132.19162
20237.2.132.192/26237.2.132.193 to 237.2.132.254237.2.132.25562
21237.2.133.0/26237.2.133.1 to 237.2.133.62237.2.133.6362
22237.2.133.64/26237.2.133.65 to 237.2.133.126237.2.133.12762
23237.2.133.128/26237.2.133.129 to 237.2.133.190237.2.133.19162
24237.2.133.192/26237.2.133.193 to 237.2.133.254237.2.133.25562
25237.2.134.0/26237.2.134.1 to 237.2.134.62237.2.134.6362
26237.2.134.64/26237.2.134.65 to 237.2.134.126237.2.134.12762
27237.2.134.128/26237.2.134.129 to 237.2.134.190237.2.134.19162
28237.2.134.192/26237.2.134.193 to 237.2.134.254237.2.134.25562
29237.2.135.0/26237.2.135.1 to 237.2.135.62237.2.135.6362
30237.2.135.64/26237.2.135.65 to 237.2.135.126237.2.135.12762
31237.2.135.128/26237.2.135.129 to 237.2.135.190237.2.135.19162
32237.2.135.192/26237.2.135.193 to 237.2.135.254237.2.135.25562
33237.2.136.0/26237.2.136.1 to 237.2.136.62237.2.136.6362
34237.2.136.64/26237.2.136.65 to 237.2.136.126237.2.136.12762
35237.2.136.128/26237.2.136.129 to 237.2.136.190237.2.136.19162
36237.2.136.192/26237.2.136.193 to 237.2.136.254237.2.136.25562
37237.2.137.0/26237.2.137.1 to 237.2.137.62237.2.137.6362
38237.2.137.64/26237.2.137.65 to 237.2.137.126237.2.137.12762
39237.2.137.128/26237.2.137.129 to 237.2.137.190237.2.137.19162
40237.2.137.192/26237.2.137.193 to 237.2.137.254237.2.137.25562
41237.2.138.0/26237.2.138.1 to 237.2.138.62237.2.138.6362
42237.2.138.64/26237.2.138.65 to 237.2.138.126237.2.138.12762
43237.2.138.128/26237.2.138.129 to 237.2.138.190237.2.138.19162
44237.2.138.192/26237.2.138.193 to 237.2.138.254237.2.138.25562
45237.2.139.0/26237.2.139.1 to 237.2.139.62237.2.139.6362
46237.2.139.64/26237.2.139.65 to 237.2.139.126237.2.139.12762
47237.2.139.128/26237.2.139.129 to 237.2.139.190237.2.139.19162
48237.2.139.192/26237.2.139.193 to 237.2.139.254237.2.139.25562
49237.2.140.0/26237.2.140.1 to 237.2.140.62237.2.140.6362
50237.2.140.64/26237.2.140.65 to 237.2.140.126237.2.140.12762
51237.2.140.128/26237.2.140.129 to 237.2.140.190237.2.140.19162
52237.2.140.192/26237.2.140.193 to 237.2.140.254237.2.140.25562
53237.2.141.0/26237.2.141.1 to 237.2.141.62237.2.141.6362
54237.2.141.64/26237.2.141.65 to 237.2.141.126237.2.141.12762
55237.2.141.128/26237.2.141.129 to 237.2.141.190237.2.141.19162
56237.2.141.192/26237.2.141.193 to 237.2.141.254237.2.141.25562
57237.2.142.0/26237.2.142.1 to 237.2.142.62237.2.142.6362
58237.2.142.64/26237.2.142.65 to 237.2.142.126237.2.142.12762
59237.2.142.128/26237.2.142.129 to 237.2.142.190237.2.142.19162
60237.2.142.192/26237.2.142.193 to 237.2.142.254237.2.142.25562
61237.2.143.0/26237.2.143.1 to 237.2.143.62237.2.143.6362
62237.2.143.64/26237.2.143.65 to 237.2.143.126237.2.143.12762
63237.2.143.128/26237.2.143.129 to 237.2.143.190237.2.143.19162
64237.2.143.192/26237.2.143.193 to 237.2.143.254237.2.143.25562
65237.2.144.0/26237.2.144.1 to 237.2.144.62237.2.144.6362
66237.2.144.64/26237.2.144.65 to 237.2.144.126237.2.144.12762
67237.2.144.128/26237.2.144.129 to 237.2.144.190237.2.144.19162
68237.2.144.192/26237.2.144.193 to 237.2.144.254237.2.144.25562
69237.2.145.0/26237.2.145.1 to 237.2.145.62237.2.145.6362
70237.2.145.64/26237.2.145.65 to 237.2.145.126237.2.145.12762
71237.2.145.128/26237.2.145.129 to 237.2.145.190237.2.145.19162
72237.2.145.192/26237.2.145.193 to 237.2.145.254237.2.145.25562
73237.2.146.0/26237.2.146.1 to 237.2.146.62237.2.146.6362
74237.2.146.64/26237.2.146.65 to 237.2.146.126237.2.146.12762
75237.2.146.128/26237.2.146.129 to 237.2.146.190237.2.146.19162
76237.2.146.192/26237.2.146.193 to 237.2.146.254237.2.146.25562
77237.2.147.0/26237.2.147.1 to 237.2.147.62237.2.147.6362
78237.2.147.64/26237.2.147.65 to 237.2.147.126237.2.147.12762
79237.2.147.128/26237.2.147.129 to 237.2.147.190237.2.147.19162
80237.2.147.192/26237.2.147.193 to 237.2.147.254237.2.147.25562
81237.2.148.0/26237.2.148.1 to 237.2.148.62237.2.148.6362
82237.2.148.64/26237.2.148.65 to 237.2.148.126237.2.148.12762
83237.2.148.128/26237.2.148.129 to 237.2.148.190237.2.148.19162
84237.2.148.192/26237.2.148.193 to 237.2.148.254237.2.148.25562
85237.2.149.0/26237.2.149.1 to 237.2.149.62237.2.149.6362
86237.2.149.64/26237.2.149.65 to 237.2.149.126237.2.149.12762
87237.2.149.128/26237.2.149.129 to 237.2.149.190237.2.149.19162
88237.2.149.192/26237.2.149.193 to 237.2.149.254237.2.149.25562
89237.2.150.0/26237.2.150.1 to 237.2.150.62237.2.150.6362
90237.2.150.64/26237.2.150.65 to 237.2.150.126237.2.150.12762
91237.2.150.128/26237.2.150.129 to 237.2.150.190237.2.150.19162
92237.2.150.192/26237.2.150.193 to 237.2.150.254237.2.150.25562
93237.2.151.0/26237.2.151.1 to 237.2.151.62237.2.151.6362
94237.2.151.64/26237.2.151.65 to 237.2.151.126237.2.151.12762
95237.2.151.128/26237.2.151.129 to 237.2.151.190237.2.151.19162
96237.2.151.192/26237.2.151.193 to 237.2.151.254237.2.151.25562
97237.2.152.0/26237.2.152.1 to 237.2.152.62237.2.152.6362
98237.2.152.64/26237.2.152.65 to 237.2.152.126237.2.152.12762
99237.2.152.128/26237.2.152.129 to 237.2.152.190237.2.152.19162
100237.2.152.192/26237.2.152.193 to 237.2.152.254237.2.152.25562
101237.2.153.0/26237.2.153.1 to 237.2.153.62237.2.153.6362
102237.2.153.64/26237.2.153.65 to 237.2.153.126237.2.153.12762
103237.2.153.128/26237.2.153.129 to 237.2.153.190237.2.153.19162
104237.2.153.192/26237.2.153.193 to 237.2.153.254237.2.153.25562
105237.2.154.0/26237.2.154.1 to 237.2.154.62237.2.154.6362
106237.2.154.64/26237.2.154.65 to 237.2.154.126237.2.154.12762
107237.2.154.128/26237.2.154.129 to 237.2.154.190237.2.154.19162
108237.2.154.192/26237.2.154.193 to 237.2.154.254237.2.154.25562
109237.2.155.0/26237.2.155.1 to 237.2.155.62237.2.155.6362
110237.2.155.64/26237.2.155.65 to 237.2.155.126237.2.155.12762
111237.2.155.128/26237.2.155.129 to 237.2.155.190237.2.155.19162
112237.2.155.192/26237.2.155.193 to 237.2.155.254237.2.155.25562
113237.2.156.0/26237.2.156.1 to 237.2.156.62237.2.156.6362
114237.2.156.64/26237.2.156.65 to 237.2.156.126237.2.156.12762
115237.2.156.128/26237.2.156.129 to 237.2.156.190237.2.156.19162
116237.2.156.192/26237.2.156.193 to 237.2.156.254237.2.156.25562
117237.2.157.0/26237.2.157.1 to 237.2.157.62237.2.157.6362
118237.2.157.64/26237.2.157.65 to 237.2.157.126237.2.157.12762
119237.2.157.128/26237.2.157.129 to 237.2.157.190237.2.157.19162
120237.2.157.192/26237.2.157.193 to 237.2.157.254237.2.157.25562
121237.2.158.0/26237.2.158.1 to 237.2.158.62237.2.158.6362
122237.2.158.64/26237.2.158.65 to 237.2.158.126237.2.158.12762
123237.2.158.128/26237.2.158.129 to 237.2.158.190237.2.158.19162
124237.2.158.192/26237.2.158.193 to 237.2.158.254237.2.158.25562
125237.2.159.0/26237.2.159.1 to 237.2.159.62237.2.159.6362
126237.2.159.64/26237.2.159.65 to 237.2.159.126237.2.159.12762
127237.2.159.128/26237.2.159.129 to 237.2.159.190237.2.159.19162
128237.2.159.192/26237.2.159.193 to 237.2.159.254237.2.159.25562

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.