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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.

Network237.64.0.0/12
Usable hosts1,048,574
Subnet mask255.240.0.0
Addresses1,048,576
Network address
237.64.0.0
Broadcast address
237.79.255.255
First usable
237.64.0.1
Last usable
237.79.255.254
Usable hosts
1,048,574 (1,048,576 less the network and broadcast addresses)
Subnet mask
255.240.0.0
Wildcard mask
0.15.255.255 (Cisco ACLs, OSPF)
Prefix length
/12
Type
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex ED400000 · Integer 3980394496 to 3981443071
Reverse DNS zones
64.237.in-addr.arpa
65.237.in-addr.arpa
66.237.in-addr.arpa
67.237.in-addr.arpa
68.237.in-addr.arpa
69.237.in-addr.arpa
70.237.in-addr.arpa
71.237.in-addr.arpa
72.237.in-addr.arpa
73.237.in-addr.arpa
74.237.in-addr.arpa
75.237.in-addr.arpa
76.237.in-addr.arpa
77.237.in-addr.arpa
78.237.in-addr.arpa
79.237.in-addr.arpa
/12 is not on a 8-bit boundary, so it takes 16 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11101101.01000000.00000000.00000000237.64.0.0
Subnet mask11111111.11110000.00000000.00000000255.240.0.0
Network11101101.01000000.00000000.00000000237.64.0.0
Broadcast11101101.01001111.11111111.11111111237.79.255.255
Split into smaller subnets/19
/13 (2)/14 (4)/15 (8)/16 (16)/17 (32)/18 (64)/19 (128)/20 (256)/21 (512)/22 (1,024)/23 (2,048)/24 (4,096)

237.64.0.0/12 makes 128 subnets of /19.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1237.64.0.0/19237.64.0.1 to 237.64.31.254237.64.31.2558,190
2237.64.32.0/19237.64.32.1 to 237.64.63.254237.64.63.2558,190
3237.64.64.0/19237.64.64.1 to 237.64.95.254237.64.95.2558,190
4237.64.96.0/19237.64.96.1 to 237.64.127.254237.64.127.2558,190
5237.64.128.0/19237.64.128.1 to 237.64.159.254237.64.159.2558,190
6237.64.160.0/19237.64.160.1 to 237.64.191.254237.64.191.2558,190
7237.64.192.0/19237.64.192.1 to 237.64.223.254237.64.223.2558,190
8237.64.224.0/19237.64.224.1 to 237.64.255.254237.64.255.2558,190
9237.65.0.0/19237.65.0.1 to 237.65.31.254237.65.31.2558,190
10237.65.32.0/19237.65.32.1 to 237.65.63.254237.65.63.2558,190
11237.65.64.0/19237.65.64.1 to 237.65.95.254237.65.95.2558,190
12237.65.96.0/19237.65.96.1 to 237.65.127.254237.65.127.2558,190
13237.65.128.0/19237.65.128.1 to 237.65.159.254237.65.159.2558,190
14237.65.160.0/19237.65.160.1 to 237.65.191.254237.65.191.2558,190
15237.65.192.0/19237.65.192.1 to 237.65.223.254237.65.223.2558,190
16237.65.224.0/19237.65.224.1 to 237.65.255.254237.65.255.2558,190
17237.66.0.0/19237.66.0.1 to 237.66.31.254237.66.31.2558,190
18237.66.32.0/19237.66.32.1 to 237.66.63.254237.66.63.2558,190
19237.66.64.0/19237.66.64.1 to 237.66.95.254237.66.95.2558,190
20237.66.96.0/19237.66.96.1 to 237.66.127.254237.66.127.2558,190
21237.66.128.0/19237.66.128.1 to 237.66.159.254237.66.159.2558,190
22237.66.160.0/19237.66.160.1 to 237.66.191.254237.66.191.2558,190
23237.66.192.0/19237.66.192.1 to 237.66.223.254237.66.223.2558,190
24237.66.224.0/19237.66.224.1 to 237.66.255.254237.66.255.2558,190
25237.67.0.0/19237.67.0.1 to 237.67.31.254237.67.31.2558,190
26237.67.32.0/19237.67.32.1 to 237.67.63.254237.67.63.2558,190
27237.67.64.0/19237.67.64.1 to 237.67.95.254237.67.95.2558,190
28237.67.96.0/19237.67.96.1 to 237.67.127.254237.67.127.2558,190
29237.67.128.0/19237.67.128.1 to 237.67.159.254237.67.159.2558,190
30237.67.160.0/19237.67.160.1 to 237.67.191.254237.67.191.2558,190
31237.67.192.0/19237.67.192.1 to 237.67.223.254237.67.223.2558,190
32237.67.224.0/19237.67.224.1 to 237.67.255.254237.67.255.2558,190
33237.68.0.0/19237.68.0.1 to 237.68.31.254237.68.31.2558,190
34237.68.32.0/19237.68.32.1 to 237.68.63.254237.68.63.2558,190
35237.68.64.0/19237.68.64.1 to 237.68.95.254237.68.95.2558,190
36237.68.96.0/19237.68.96.1 to 237.68.127.254237.68.127.2558,190
37237.68.128.0/19237.68.128.1 to 237.68.159.254237.68.159.2558,190
38237.68.160.0/19237.68.160.1 to 237.68.191.254237.68.191.2558,190
39237.68.192.0/19237.68.192.1 to 237.68.223.254237.68.223.2558,190
40237.68.224.0/19237.68.224.1 to 237.68.255.254237.68.255.2558,190
41237.69.0.0/19237.69.0.1 to 237.69.31.254237.69.31.2558,190
42237.69.32.0/19237.69.32.1 to 237.69.63.254237.69.63.2558,190
43237.69.64.0/19237.69.64.1 to 237.69.95.254237.69.95.2558,190
44237.69.96.0/19237.69.96.1 to 237.69.127.254237.69.127.2558,190
45237.69.128.0/19237.69.128.1 to 237.69.159.254237.69.159.2558,190
46237.69.160.0/19237.69.160.1 to 237.69.191.254237.69.191.2558,190
47237.69.192.0/19237.69.192.1 to 237.69.223.254237.69.223.2558,190
48237.69.224.0/19237.69.224.1 to 237.69.255.254237.69.255.2558,190
49237.70.0.0/19237.70.0.1 to 237.70.31.254237.70.31.2558,190
50237.70.32.0/19237.70.32.1 to 237.70.63.254237.70.63.2558,190
51237.70.64.0/19237.70.64.1 to 237.70.95.254237.70.95.2558,190
52237.70.96.0/19237.70.96.1 to 237.70.127.254237.70.127.2558,190
53237.70.128.0/19237.70.128.1 to 237.70.159.254237.70.159.2558,190
54237.70.160.0/19237.70.160.1 to 237.70.191.254237.70.191.2558,190
55237.70.192.0/19237.70.192.1 to 237.70.223.254237.70.223.2558,190
56237.70.224.0/19237.70.224.1 to 237.70.255.254237.70.255.2558,190
57237.71.0.0/19237.71.0.1 to 237.71.31.254237.71.31.2558,190
58237.71.32.0/19237.71.32.1 to 237.71.63.254237.71.63.2558,190
59237.71.64.0/19237.71.64.1 to 237.71.95.254237.71.95.2558,190
60237.71.96.0/19237.71.96.1 to 237.71.127.254237.71.127.2558,190
61237.71.128.0/19237.71.128.1 to 237.71.159.254237.71.159.2558,190
62237.71.160.0/19237.71.160.1 to 237.71.191.254237.71.191.2558,190
63237.71.192.0/19237.71.192.1 to 237.71.223.254237.71.223.2558,190
64237.71.224.0/19237.71.224.1 to 237.71.255.254237.71.255.2558,190
65237.72.0.0/19237.72.0.1 to 237.72.31.254237.72.31.2558,190
66237.72.32.0/19237.72.32.1 to 237.72.63.254237.72.63.2558,190
67237.72.64.0/19237.72.64.1 to 237.72.95.254237.72.95.2558,190
68237.72.96.0/19237.72.96.1 to 237.72.127.254237.72.127.2558,190
69237.72.128.0/19237.72.128.1 to 237.72.159.254237.72.159.2558,190
70237.72.160.0/19237.72.160.1 to 237.72.191.254237.72.191.2558,190
71237.72.192.0/19237.72.192.1 to 237.72.223.254237.72.223.2558,190
72237.72.224.0/19237.72.224.1 to 237.72.255.254237.72.255.2558,190
73237.73.0.0/19237.73.0.1 to 237.73.31.254237.73.31.2558,190
74237.73.32.0/19237.73.32.1 to 237.73.63.254237.73.63.2558,190
75237.73.64.0/19237.73.64.1 to 237.73.95.254237.73.95.2558,190
76237.73.96.0/19237.73.96.1 to 237.73.127.254237.73.127.2558,190
77237.73.128.0/19237.73.128.1 to 237.73.159.254237.73.159.2558,190
78237.73.160.0/19237.73.160.1 to 237.73.191.254237.73.191.2558,190
79237.73.192.0/19237.73.192.1 to 237.73.223.254237.73.223.2558,190
80237.73.224.0/19237.73.224.1 to 237.73.255.254237.73.255.2558,190
81237.74.0.0/19237.74.0.1 to 237.74.31.254237.74.31.2558,190
82237.74.32.0/19237.74.32.1 to 237.74.63.254237.74.63.2558,190
83237.74.64.0/19237.74.64.1 to 237.74.95.254237.74.95.2558,190
84237.74.96.0/19237.74.96.1 to 237.74.127.254237.74.127.2558,190
85237.74.128.0/19237.74.128.1 to 237.74.159.254237.74.159.2558,190
86237.74.160.0/19237.74.160.1 to 237.74.191.254237.74.191.2558,190
87237.74.192.0/19237.74.192.1 to 237.74.223.254237.74.223.2558,190
88237.74.224.0/19237.74.224.1 to 237.74.255.254237.74.255.2558,190
89237.75.0.0/19237.75.0.1 to 237.75.31.254237.75.31.2558,190
90237.75.32.0/19237.75.32.1 to 237.75.63.254237.75.63.2558,190
91237.75.64.0/19237.75.64.1 to 237.75.95.254237.75.95.2558,190
92237.75.96.0/19237.75.96.1 to 237.75.127.254237.75.127.2558,190
93237.75.128.0/19237.75.128.1 to 237.75.159.254237.75.159.2558,190
94237.75.160.0/19237.75.160.1 to 237.75.191.254237.75.191.2558,190
95237.75.192.0/19237.75.192.1 to 237.75.223.254237.75.223.2558,190
96237.75.224.0/19237.75.224.1 to 237.75.255.254237.75.255.2558,190
97237.76.0.0/19237.76.0.1 to 237.76.31.254237.76.31.2558,190
98237.76.32.0/19237.76.32.1 to 237.76.63.254237.76.63.2558,190
99237.76.64.0/19237.76.64.1 to 237.76.95.254237.76.95.2558,190
100237.76.96.0/19237.76.96.1 to 237.76.127.254237.76.127.2558,190
101237.76.128.0/19237.76.128.1 to 237.76.159.254237.76.159.2558,190
102237.76.160.0/19237.76.160.1 to 237.76.191.254237.76.191.2558,190
103237.76.192.0/19237.76.192.1 to 237.76.223.254237.76.223.2558,190
104237.76.224.0/19237.76.224.1 to 237.76.255.254237.76.255.2558,190
105237.77.0.0/19237.77.0.1 to 237.77.31.254237.77.31.2558,190
106237.77.32.0/19237.77.32.1 to 237.77.63.254237.77.63.2558,190
107237.77.64.0/19237.77.64.1 to 237.77.95.254237.77.95.2558,190
108237.77.96.0/19237.77.96.1 to 237.77.127.254237.77.127.2558,190
109237.77.128.0/19237.77.128.1 to 237.77.159.254237.77.159.2558,190
110237.77.160.0/19237.77.160.1 to 237.77.191.254237.77.191.2558,190
111237.77.192.0/19237.77.192.1 to 237.77.223.254237.77.223.2558,190
112237.77.224.0/19237.77.224.1 to 237.77.255.254237.77.255.2558,190
113237.78.0.0/19237.78.0.1 to 237.78.31.254237.78.31.2558,190
114237.78.32.0/19237.78.32.1 to 237.78.63.254237.78.63.2558,190
115237.78.64.0/19237.78.64.1 to 237.78.95.254237.78.95.2558,190
116237.78.96.0/19237.78.96.1 to 237.78.127.254237.78.127.2558,190
117237.78.128.0/19237.78.128.1 to 237.78.159.254237.78.159.2558,190
118237.78.160.0/19237.78.160.1 to 237.78.191.254237.78.191.2558,190
119237.78.192.0/19237.78.192.1 to 237.78.223.254237.78.223.2558,190
120237.78.224.0/19237.78.224.1 to 237.78.255.254237.78.255.2558,190
121237.79.0.0/19237.79.0.1 to 237.79.31.254237.79.31.2558,190
122237.79.32.0/19237.79.32.1 to 237.79.63.254237.79.63.2558,190
123237.79.64.0/19237.79.64.1 to 237.79.95.254237.79.95.2558,190
124237.79.96.0/19237.79.96.1 to 237.79.127.254237.79.127.2558,190
125237.79.128.0/19237.79.128.1 to 237.79.159.254237.79.159.2558,190
126237.79.160.0/19237.79.160.1 to 237.79.191.254237.79.191.2558,190
127237.79.192.0/19237.79.192.1 to 237.79.223.254237.79.223.2558,190
128237.79.224.0/19237.79.224.1 to 237.79.255.254237.79.255.2558,190

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.