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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.

Network138.2.0.0/17
Usable hosts32,766
Subnet mask255.255.128.0
Addresses32,768
Network address
138.2.0.0
Broadcast address
138.2.127.255
First usable
138.2.0.1
Last usable
138.2.127.254
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
Public public
Old class
B (default /16)
As numbers
Hex 8A020000 · Integer 2315386880 to 2315419647
Reverse DNS zones
0.2.138.in-addr.arpa
1.2.138.in-addr.arpa
2.2.138.in-addr.arpa
3.2.138.in-addr.arpa
4.2.138.in-addr.arpa
5.2.138.in-addr.arpa
6.2.138.in-addr.arpa
7.2.138.in-addr.arpa
8.2.138.in-addr.arpa
9.2.138.in-addr.arpa
10.2.138.in-addr.arpa
11.2.138.in-addr.arpa
12.2.138.in-addr.arpa
13.2.138.in-addr.arpa
14.2.138.in-addr.arpa
15.2.138.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
Address10001010.00000010.00000000.00000000138.2.0.0
Subnet mask11111111.11111111.10000000.00000000255.255.128.0
Network10001010.00000010.00000000.00000000138.2.0.0
Broadcast10001010.00000010.01111111.11111111138.2.127.255
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)

138.2.0.0/17 makes 128 subnets of /24.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1138.2.0.0/24138.2.0.1 to 138.2.0.254138.2.0.255254
2138.2.1.0/24138.2.1.1 to 138.2.1.254138.2.1.255254
3138.2.2.0/24138.2.2.1 to 138.2.2.254138.2.2.255254
4138.2.3.0/24138.2.3.1 to 138.2.3.254138.2.3.255254
5138.2.4.0/24138.2.4.1 to 138.2.4.254138.2.4.255254
6138.2.5.0/24138.2.5.1 to 138.2.5.254138.2.5.255254
7138.2.6.0/24138.2.6.1 to 138.2.6.254138.2.6.255254
8138.2.7.0/24138.2.7.1 to 138.2.7.254138.2.7.255254
9138.2.8.0/24138.2.8.1 to 138.2.8.254138.2.8.255254
10138.2.9.0/24138.2.9.1 to 138.2.9.254138.2.9.255254
11138.2.10.0/24138.2.10.1 to 138.2.10.254138.2.10.255254
12138.2.11.0/24138.2.11.1 to 138.2.11.254138.2.11.255254
13138.2.12.0/24138.2.12.1 to 138.2.12.254138.2.12.255254
14138.2.13.0/24138.2.13.1 to 138.2.13.254138.2.13.255254
15138.2.14.0/24138.2.14.1 to 138.2.14.254138.2.14.255254
16138.2.15.0/24138.2.15.1 to 138.2.15.254138.2.15.255254
17138.2.16.0/24138.2.16.1 to 138.2.16.254138.2.16.255254
18138.2.17.0/24138.2.17.1 to 138.2.17.254138.2.17.255254
19138.2.18.0/24138.2.18.1 to 138.2.18.254138.2.18.255254
20138.2.19.0/24138.2.19.1 to 138.2.19.254138.2.19.255254
21138.2.20.0/24138.2.20.1 to 138.2.20.254138.2.20.255254
22138.2.21.0/24138.2.21.1 to 138.2.21.254138.2.21.255254
23138.2.22.0/24138.2.22.1 to 138.2.22.254138.2.22.255254
24138.2.23.0/24138.2.23.1 to 138.2.23.254138.2.23.255254
25138.2.24.0/24138.2.24.1 to 138.2.24.254138.2.24.255254
26138.2.25.0/24138.2.25.1 to 138.2.25.254138.2.25.255254
27138.2.26.0/24138.2.26.1 to 138.2.26.254138.2.26.255254
28138.2.27.0/24138.2.27.1 to 138.2.27.254138.2.27.255254
29138.2.28.0/24138.2.28.1 to 138.2.28.254138.2.28.255254
30138.2.29.0/24138.2.29.1 to 138.2.29.254138.2.29.255254
31138.2.30.0/24138.2.30.1 to 138.2.30.254138.2.30.255254
32138.2.31.0/24138.2.31.1 to 138.2.31.254138.2.31.255254
33138.2.32.0/24138.2.32.1 to 138.2.32.254138.2.32.255254
34138.2.33.0/24138.2.33.1 to 138.2.33.254138.2.33.255254
35138.2.34.0/24138.2.34.1 to 138.2.34.254138.2.34.255254
36138.2.35.0/24138.2.35.1 to 138.2.35.254138.2.35.255254
37138.2.36.0/24138.2.36.1 to 138.2.36.254138.2.36.255254
38138.2.37.0/24138.2.37.1 to 138.2.37.254138.2.37.255254
39138.2.38.0/24138.2.38.1 to 138.2.38.254138.2.38.255254
40138.2.39.0/24138.2.39.1 to 138.2.39.254138.2.39.255254
41138.2.40.0/24138.2.40.1 to 138.2.40.254138.2.40.255254
42138.2.41.0/24138.2.41.1 to 138.2.41.254138.2.41.255254
43138.2.42.0/24138.2.42.1 to 138.2.42.254138.2.42.255254
44138.2.43.0/24138.2.43.1 to 138.2.43.254138.2.43.255254
45138.2.44.0/24138.2.44.1 to 138.2.44.254138.2.44.255254
46138.2.45.0/24138.2.45.1 to 138.2.45.254138.2.45.255254
47138.2.46.0/24138.2.46.1 to 138.2.46.254138.2.46.255254
48138.2.47.0/24138.2.47.1 to 138.2.47.254138.2.47.255254
49138.2.48.0/24138.2.48.1 to 138.2.48.254138.2.48.255254
50138.2.49.0/24138.2.49.1 to 138.2.49.254138.2.49.255254
51138.2.50.0/24138.2.50.1 to 138.2.50.254138.2.50.255254
52138.2.51.0/24138.2.51.1 to 138.2.51.254138.2.51.255254
53138.2.52.0/24138.2.52.1 to 138.2.52.254138.2.52.255254
54138.2.53.0/24138.2.53.1 to 138.2.53.254138.2.53.255254
55138.2.54.0/24138.2.54.1 to 138.2.54.254138.2.54.255254
56138.2.55.0/24138.2.55.1 to 138.2.55.254138.2.55.255254
57138.2.56.0/24138.2.56.1 to 138.2.56.254138.2.56.255254
58138.2.57.0/24138.2.57.1 to 138.2.57.254138.2.57.255254
59138.2.58.0/24138.2.58.1 to 138.2.58.254138.2.58.255254
60138.2.59.0/24138.2.59.1 to 138.2.59.254138.2.59.255254
61138.2.60.0/24138.2.60.1 to 138.2.60.254138.2.60.255254
62138.2.61.0/24138.2.61.1 to 138.2.61.254138.2.61.255254
63138.2.62.0/24138.2.62.1 to 138.2.62.254138.2.62.255254
64138.2.63.0/24138.2.63.1 to 138.2.63.254138.2.63.255254
65138.2.64.0/24138.2.64.1 to 138.2.64.254138.2.64.255254
66138.2.65.0/24138.2.65.1 to 138.2.65.254138.2.65.255254
67138.2.66.0/24138.2.66.1 to 138.2.66.254138.2.66.255254
68138.2.67.0/24138.2.67.1 to 138.2.67.254138.2.67.255254
69138.2.68.0/24138.2.68.1 to 138.2.68.254138.2.68.255254
70138.2.69.0/24138.2.69.1 to 138.2.69.254138.2.69.255254
71138.2.70.0/24138.2.70.1 to 138.2.70.254138.2.70.255254
72138.2.71.0/24138.2.71.1 to 138.2.71.254138.2.71.255254
73138.2.72.0/24138.2.72.1 to 138.2.72.254138.2.72.255254
74138.2.73.0/24138.2.73.1 to 138.2.73.254138.2.73.255254
75138.2.74.0/24138.2.74.1 to 138.2.74.254138.2.74.255254
76138.2.75.0/24138.2.75.1 to 138.2.75.254138.2.75.255254
77138.2.76.0/24138.2.76.1 to 138.2.76.254138.2.76.255254
78138.2.77.0/24138.2.77.1 to 138.2.77.254138.2.77.255254
79138.2.78.0/24138.2.78.1 to 138.2.78.254138.2.78.255254
80138.2.79.0/24138.2.79.1 to 138.2.79.254138.2.79.255254
81138.2.80.0/24138.2.80.1 to 138.2.80.254138.2.80.255254
82138.2.81.0/24138.2.81.1 to 138.2.81.254138.2.81.255254
83138.2.82.0/24138.2.82.1 to 138.2.82.254138.2.82.255254
84138.2.83.0/24138.2.83.1 to 138.2.83.254138.2.83.255254
85138.2.84.0/24138.2.84.1 to 138.2.84.254138.2.84.255254
86138.2.85.0/24138.2.85.1 to 138.2.85.254138.2.85.255254
87138.2.86.0/24138.2.86.1 to 138.2.86.254138.2.86.255254
88138.2.87.0/24138.2.87.1 to 138.2.87.254138.2.87.255254
89138.2.88.0/24138.2.88.1 to 138.2.88.254138.2.88.255254
90138.2.89.0/24138.2.89.1 to 138.2.89.254138.2.89.255254
91138.2.90.0/24138.2.90.1 to 138.2.90.254138.2.90.255254
92138.2.91.0/24138.2.91.1 to 138.2.91.254138.2.91.255254
93138.2.92.0/24138.2.92.1 to 138.2.92.254138.2.92.255254
94138.2.93.0/24138.2.93.1 to 138.2.93.254138.2.93.255254
95138.2.94.0/24138.2.94.1 to 138.2.94.254138.2.94.255254
96138.2.95.0/24138.2.95.1 to 138.2.95.254138.2.95.255254
97138.2.96.0/24138.2.96.1 to 138.2.96.254138.2.96.255254
98138.2.97.0/24138.2.97.1 to 138.2.97.254138.2.97.255254
99138.2.98.0/24138.2.98.1 to 138.2.98.254138.2.98.255254
100138.2.99.0/24138.2.99.1 to 138.2.99.254138.2.99.255254
101138.2.100.0/24138.2.100.1 to 138.2.100.254138.2.100.255254
102138.2.101.0/24138.2.101.1 to 138.2.101.254138.2.101.255254
103138.2.102.0/24138.2.102.1 to 138.2.102.254138.2.102.255254
104138.2.103.0/24138.2.103.1 to 138.2.103.254138.2.103.255254
105138.2.104.0/24138.2.104.1 to 138.2.104.254138.2.104.255254
106138.2.105.0/24138.2.105.1 to 138.2.105.254138.2.105.255254
107138.2.106.0/24138.2.106.1 to 138.2.106.254138.2.106.255254
108138.2.107.0/24138.2.107.1 to 138.2.107.254138.2.107.255254
109138.2.108.0/24138.2.108.1 to 138.2.108.254138.2.108.255254
110138.2.109.0/24138.2.109.1 to 138.2.109.254138.2.109.255254
111138.2.110.0/24138.2.110.1 to 138.2.110.254138.2.110.255254
112138.2.111.0/24138.2.111.1 to 138.2.111.254138.2.111.255254
113138.2.112.0/24138.2.112.1 to 138.2.112.254138.2.112.255254
114138.2.113.0/24138.2.113.1 to 138.2.113.254138.2.113.255254
115138.2.114.0/24138.2.114.1 to 138.2.114.254138.2.114.255254
116138.2.115.0/24138.2.115.1 to 138.2.115.254138.2.115.255254
117138.2.116.0/24138.2.116.1 to 138.2.116.254138.2.116.255254
118138.2.117.0/24138.2.117.1 to 138.2.117.254138.2.117.255254
119138.2.118.0/24138.2.118.1 to 138.2.118.254138.2.118.255254
120138.2.119.0/24138.2.119.1 to 138.2.119.254138.2.119.255254
121138.2.120.0/24138.2.120.1 to 138.2.120.254138.2.120.255254
122138.2.121.0/24138.2.121.1 to 138.2.121.254138.2.121.255254
123138.2.122.0/24138.2.122.1 to 138.2.122.254138.2.122.255254
124138.2.123.0/24138.2.123.1 to 138.2.123.254138.2.123.255254
125138.2.124.0/24138.2.124.1 to 138.2.124.254138.2.124.255254
126138.2.125.0/24138.2.125.1 to 138.2.125.254138.2.125.255254
127138.2.126.0/24138.2.126.1 to 138.2.126.254138.2.126.255254
128138.2.127.0/24138.2.127.1 to 138.2.127.254138.2.127.255254

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.