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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.

Network251.208.0.0/12
Usable hosts1,048,574
Subnet mask255.240.0.0
Addresses1,048,576
Network address
251.208.0.0
Broadcast address
251.223.255.255
First usable
251.208.0.1
Last usable
251.223.255.254
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
Reserved 240.0.0.0/4
Future use; not usable on most systems
Old class
E (reserved)
As numbers
Hex FBD00000 · Integer 4224712704 to 4225761279
Reverse DNS zones
208.251.in-addr.arpa
209.251.in-addr.arpa
210.251.in-addr.arpa
211.251.in-addr.arpa
212.251.in-addr.arpa
213.251.in-addr.arpa
214.251.in-addr.arpa
215.251.in-addr.arpa
216.251.in-addr.arpa
217.251.in-addr.arpa
218.251.in-addr.arpa
219.251.in-addr.arpa
220.251.in-addr.arpa
221.251.in-addr.arpa
222.251.in-addr.arpa
223.251.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
Address11111011.11010000.00000000.00000000251.208.0.0
Subnet mask11111111.11110000.00000000.00000000255.240.0.0
Network11111011.11010000.00000000.00000000251.208.0.0
Broadcast11111011.11011111.11111111.11111111251.223.255.255
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)

251.208.0.0/12 makes 128 subnets of /19.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1251.208.0.0/19251.208.0.1 to 251.208.31.254251.208.31.2558,190
2251.208.32.0/19251.208.32.1 to 251.208.63.254251.208.63.2558,190
3251.208.64.0/19251.208.64.1 to 251.208.95.254251.208.95.2558,190
4251.208.96.0/19251.208.96.1 to 251.208.127.254251.208.127.2558,190
5251.208.128.0/19251.208.128.1 to 251.208.159.254251.208.159.2558,190
6251.208.160.0/19251.208.160.1 to 251.208.191.254251.208.191.2558,190
7251.208.192.0/19251.208.192.1 to 251.208.223.254251.208.223.2558,190
8251.208.224.0/19251.208.224.1 to 251.208.255.254251.208.255.2558,190
9251.209.0.0/19251.209.0.1 to 251.209.31.254251.209.31.2558,190
10251.209.32.0/19251.209.32.1 to 251.209.63.254251.209.63.2558,190
11251.209.64.0/19251.209.64.1 to 251.209.95.254251.209.95.2558,190
12251.209.96.0/19251.209.96.1 to 251.209.127.254251.209.127.2558,190
13251.209.128.0/19251.209.128.1 to 251.209.159.254251.209.159.2558,190
14251.209.160.0/19251.209.160.1 to 251.209.191.254251.209.191.2558,190
15251.209.192.0/19251.209.192.1 to 251.209.223.254251.209.223.2558,190
16251.209.224.0/19251.209.224.1 to 251.209.255.254251.209.255.2558,190
17251.210.0.0/19251.210.0.1 to 251.210.31.254251.210.31.2558,190
18251.210.32.0/19251.210.32.1 to 251.210.63.254251.210.63.2558,190
19251.210.64.0/19251.210.64.1 to 251.210.95.254251.210.95.2558,190
20251.210.96.0/19251.210.96.1 to 251.210.127.254251.210.127.2558,190
21251.210.128.0/19251.210.128.1 to 251.210.159.254251.210.159.2558,190
22251.210.160.0/19251.210.160.1 to 251.210.191.254251.210.191.2558,190
23251.210.192.0/19251.210.192.1 to 251.210.223.254251.210.223.2558,190
24251.210.224.0/19251.210.224.1 to 251.210.255.254251.210.255.2558,190
25251.211.0.0/19251.211.0.1 to 251.211.31.254251.211.31.2558,190
26251.211.32.0/19251.211.32.1 to 251.211.63.254251.211.63.2558,190
27251.211.64.0/19251.211.64.1 to 251.211.95.254251.211.95.2558,190
28251.211.96.0/19251.211.96.1 to 251.211.127.254251.211.127.2558,190
29251.211.128.0/19251.211.128.1 to 251.211.159.254251.211.159.2558,190
30251.211.160.0/19251.211.160.1 to 251.211.191.254251.211.191.2558,190
31251.211.192.0/19251.211.192.1 to 251.211.223.254251.211.223.2558,190
32251.211.224.0/19251.211.224.1 to 251.211.255.254251.211.255.2558,190
33251.212.0.0/19251.212.0.1 to 251.212.31.254251.212.31.2558,190
34251.212.32.0/19251.212.32.1 to 251.212.63.254251.212.63.2558,190
35251.212.64.0/19251.212.64.1 to 251.212.95.254251.212.95.2558,190
36251.212.96.0/19251.212.96.1 to 251.212.127.254251.212.127.2558,190
37251.212.128.0/19251.212.128.1 to 251.212.159.254251.212.159.2558,190
38251.212.160.0/19251.212.160.1 to 251.212.191.254251.212.191.2558,190
39251.212.192.0/19251.212.192.1 to 251.212.223.254251.212.223.2558,190
40251.212.224.0/19251.212.224.1 to 251.212.255.254251.212.255.2558,190
41251.213.0.0/19251.213.0.1 to 251.213.31.254251.213.31.2558,190
42251.213.32.0/19251.213.32.1 to 251.213.63.254251.213.63.2558,190
43251.213.64.0/19251.213.64.1 to 251.213.95.254251.213.95.2558,190
44251.213.96.0/19251.213.96.1 to 251.213.127.254251.213.127.2558,190
45251.213.128.0/19251.213.128.1 to 251.213.159.254251.213.159.2558,190
46251.213.160.0/19251.213.160.1 to 251.213.191.254251.213.191.2558,190
47251.213.192.0/19251.213.192.1 to 251.213.223.254251.213.223.2558,190
48251.213.224.0/19251.213.224.1 to 251.213.255.254251.213.255.2558,190
49251.214.0.0/19251.214.0.1 to 251.214.31.254251.214.31.2558,190
50251.214.32.0/19251.214.32.1 to 251.214.63.254251.214.63.2558,190
51251.214.64.0/19251.214.64.1 to 251.214.95.254251.214.95.2558,190
52251.214.96.0/19251.214.96.1 to 251.214.127.254251.214.127.2558,190
53251.214.128.0/19251.214.128.1 to 251.214.159.254251.214.159.2558,190
54251.214.160.0/19251.214.160.1 to 251.214.191.254251.214.191.2558,190
55251.214.192.0/19251.214.192.1 to 251.214.223.254251.214.223.2558,190
56251.214.224.0/19251.214.224.1 to 251.214.255.254251.214.255.2558,190
57251.215.0.0/19251.215.0.1 to 251.215.31.254251.215.31.2558,190
58251.215.32.0/19251.215.32.1 to 251.215.63.254251.215.63.2558,190
59251.215.64.0/19251.215.64.1 to 251.215.95.254251.215.95.2558,190
60251.215.96.0/19251.215.96.1 to 251.215.127.254251.215.127.2558,190
61251.215.128.0/19251.215.128.1 to 251.215.159.254251.215.159.2558,190
62251.215.160.0/19251.215.160.1 to 251.215.191.254251.215.191.2558,190
63251.215.192.0/19251.215.192.1 to 251.215.223.254251.215.223.2558,190
64251.215.224.0/19251.215.224.1 to 251.215.255.254251.215.255.2558,190
65251.216.0.0/19251.216.0.1 to 251.216.31.254251.216.31.2558,190
66251.216.32.0/19251.216.32.1 to 251.216.63.254251.216.63.2558,190
67251.216.64.0/19251.216.64.1 to 251.216.95.254251.216.95.2558,190
68251.216.96.0/19251.216.96.1 to 251.216.127.254251.216.127.2558,190
69251.216.128.0/19251.216.128.1 to 251.216.159.254251.216.159.2558,190
70251.216.160.0/19251.216.160.1 to 251.216.191.254251.216.191.2558,190
71251.216.192.0/19251.216.192.1 to 251.216.223.254251.216.223.2558,190
72251.216.224.0/19251.216.224.1 to 251.216.255.254251.216.255.2558,190
73251.217.0.0/19251.217.0.1 to 251.217.31.254251.217.31.2558,190
74251.217.32.0/19251.217.32.1 to 251.217.63.254251.217.63.2558,190
75251.217.64.0/19251.217.64.1 to 251.217.95.254251.217.95.2558,190
76251.217.96.0/19251.217.96.1 to 251.217.127.254251.217.127.2558,190
77251.217.128.0/19251.217.128.1 to 251.217.159.254251.217.159.2558,190
78251.217.160.0/19251.217.160.1 to 251.217.191.254251.217.191.2558,190
79251.217.192.0/19251.217.192.1 to 251.217.223.254251.217.223.2558,190
80251.217.224.0/19251.217.224.1 to 251.217.255.254251.217.255.2558,190
81251.218.0.0/19251.218.0.1 to 251.218.31.254251.218.31.2558,190
82251.218.32.0/19251.218.32.1 to 251.218.63.254251.218.63.2558,190
83251.218.64.0/19251.218.64.1 to 251.218.95.254251.218.95.2558,190
84251.218.96.0/19251.218.96.1 to 251.218.127.254251.218.127.2558,190
85251.218.128.0/19251.218.128.1 to 251.218.159.254251.218.159.2558,190
86251.218.160.0/19251.218.160.1 to 251.218.191.254251.218.191.2558,190
87251.218.192.0/19251.218.192.1 to 251.218.223.254251.218.223.2558,190
88251.218.224.0/19251.218.224.1 to 251.218.255.254251.218.255.2558,190
89251.219.0.0/19251.219.0.1 to 251.219.31.254251.219.31.2558,190
90251.219.32.0/19251.219.32.1 to 251.219.63.254251.219.63.2558,190
91251.219.64.0/19251.219.64.1 to 251.219.95.254251.219.95.2558,190
92251.219.96.0/19251.219.96.1 to 251.219.127.254251.219.127.2558,190
93251.219.128.0/19251.219.128.1 to 251.219.159.254251.219.159.2558,190
94251.219.160.0/19251.219.160.1 to 251.219.191.254251.219.191.2558,190
95251.219.192.0/19251.219.192.1 to 251.219.223.254251.219.223.2558,190
96251.219.224.0/19251.219.224.1 to 251.219.255.254251.219.255.2558,190
97251.220.0.0/19251.220.0.1 to 251.220.31.254251.220.31.2558,190
98251.220.32.0/19251.220.32.1 to 251.220.63.254251.220.63.2558,190
99251.220.64.0/19251.220.64.1 to 251.220.95.254251.220.95.2558,190
100251.220.96.0/19251.220.96.1 to 251.220.127.254251.220.127.2558,190
101251.220.128.0/19251.220.128.1 to 251.220.159.254251.220.159.2558,190
102251.220.160.0/19251.220.160.1 to 251.220.191.254251.220.191.2558,190
103251.220.192.0/19251.220.192.1 to 251.220.223.254251.220.223.2558,190
104251.220.224.0/19251.220.224.1 to 251.220.255.254251.220.255.2558,190
105251.221.0.0/19251.221.0.1 to 251.221.31.254251.221.31.2558,190
106251.221.32.0/19251.221.32.1 to 251.221.63.254251.221.63.2558,190
107251.221.64.0/19251.221.64.1 to 251.221.95.254251.221.95.2558,190
108251.221.96.0/19251.221.96.1 to 251.221.127.254251.221.127.2558,190
109251.221.128.0/19251.221.128.1 to 251.221.159.254251.221.159.2558,190
110251.221.160.0/19251.221.160.1 to 251.221.191.254251.221.191.2558,190
111251.221.192.0/19251.221.192.1 to 251.221.223.254251.221.223.2558,190
112251.221.224.0/19251.221.224.1 to 251.221.255.254251.221.255.2558,190
113251.222.0.0/19251.222.0.1 to 251.222.31.254251.222.31.2558,190
114251.222.32.0/19251.222.32.1 to 251.222.63.254251.222.63.2558,190
115251.222.64.0/19251.222.64.1 to 251.222.95.254251.222.95.2558,190
116251.222.96.0/19251.222.96.1 to 251.222.127.254251.222.127.2558,190
117251.222.128.0/19251.222.128.1 to 251.222.159.254251.222.159.2558,190
118251.222.160.0/19251.222.160.1 to 251.222.191.254251.222.191.2558,190
119251.222.192.0/19251.222.192.1 to 251.222.223.254251.222.223.2558,190
120251.222.224.0/19251.222.224.1 to 251.222.255.254251.222.255.2558,190
121251.223.0.0/19251.223.0.1 to 251.223.31.254251.223.31.2558,190
122251.223.32.0/19251.223.32.1 to 251.223.63.254251.223.63.2558,190
123251.223.64.0/19251.223.64.1 to 251.223.95.254251.223.95.2558,190
124251.223.96.0/19251.223.96.1 to 251.223.127.254251.223.127.2558,190
125251.223.128.0/19251.223.128.1 to 251.223.159.254251.223.159.2558,190
126251.223.160.0/19251.223.160.1 to 251.223.191.254251.223.191.2558,190
127251.223.192.0/19251.223.192.1 to 251.223.223.254251.223.223.2558,190
128251.223.224.0/19251.223.224.1 to 251.223.255.254251.223.255.2558,190

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.