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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.

Network136.20.0.0/17
Usable hosts32,766
Subnet mask255.255.128.0
Addresses32,768
Network address
136.20.0.0
Broadcast address
136.20.127.255
First usable
136.20.0.1
Last usable
136.20.127.254
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 88140000 · Integer 2283012096 to 2283044863
Reverse DNS zones
0.20.136.in-addr.arpa
1.20.136.in-addr.arpa
2.20.136.in-addr.arpa
3.20.136.in-addr.arpa
4.20.136.in-addr.arpa
5.20.136.in-addr.arpa
6.20.136.in-addr.arpa
7.20.136.in-addr.arpa
8.20.136.in-addr.arpa
9.20.136.in-addr.arpa
10.20.136.in-addr.arpa
11.20.136.in-addr.arpa
12.20.136.in-addr.arpa
13.20.136.in-addr.arpa
14.20.136.in-addr.arpa
15.20.136.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
Address10001000.00010100.00000000.00000000136.20.0.0
Subnet mask11111111.11111111.10000000.00000000255.255.128.0
Network10001000.00010100.00000000.00000000136.20.0.0
Broadcast10001000.00010100.01111111.11111111136.20.127.255
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)

136.20.0.0/17 makes 128 subnets of /24.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1136.20.0.0/24136.20.0.1 to 136.20.0.254136.20.0.255254
2136.20.1.0/24136.20.1.1 to 136.20.1.254136.20.1.255254
3136.20.2.0/24136.20.2.1 to 136.20.2.254136.20.2.255254
4136.20.3.0/24136.20.3.1 to 136.20.3.254136.20.3.255254
5136.20.4.0/24136.20.4.1 to 136.20.4.254136.20.4.255254
6136.20.5.0/24136.20.5.1 to 136.20.5.254136.20.5.255254
7136.20.6.0/24136.20.6.1 to 136.20.6.254136.20.6.255254
8136.20.7.0/24136.20.7.1 to 136.20.7.254136.20.7.255254
9136.20.8.0/24136.20.8.1 to 136.20.8.254136.20.8.255254
10136.20.9.0/24136.20.9.1 to 136.20.9.254136.20.9.255254
11136.20.10.0/24136.20.10.1 to 136.20.10.254136.20.10.255254
12136.20.11.0/24136.20.11.1 to 136.20.11.254136.20.11.255254
13136.20.12.0/24136.20.12.1 to 136.20.12.254136.20.12.255254
14136.20.13.0/24136.20.13.1 to 136.20.13.254136.20.13.255254
15136.20.14.0/24136.20.14.1 to 136.20.14.254136.20.14.255254
16136.20.15.0/24136.20.15.1 to 136.20.15.254136.20.15.255254
17136.20.16.0/24136.20.16.1 to 136.20.16.254136.20.16.255254
18136.20.17.0/24136.20.17.1 to 136.20.17.254136.20.17.255254
19136.20.18.0/24136.20.18.1 to 136.20.18.254136.20.18.255254
20136.20.19.0/24136.20.19.1 to 136.20.19.254136.20.19.255254
21136.20.20.0/24136.20.20.1 to 136.20.20.254136.20.20.255254
22136.20.21.0/24136.20.21.1 to 136.20.21.254136.20.21.255254
23136.20.22.0/24136.20.22.1 to 136.20.22.254136.20.22.255254
24136.20.23.0/24136.20.23.1 to 136.20.23.254136.20.23.255254
25136.20.24.0/24136.20.24.1 to 136.20.24.254136.20.24.255254
26136.20.25.0/24136.20.25.1 to 136.20.25.254136.20.25.255254
27136.20.26.0/24136.20.26.1 to 136.20.26.254136.20.26.255254
28136.20.27.0/24136.20.27.1 to 136.20.27.254136.20.27.255254
29136.20.28.0/24136.20.28.1 to 136.20.28.254136.20.28.255254
30136.20.29.0/24136.20.29.1 to 136.20.29.254136.20.29.255254
31136.20.30.0/24136.20.30.1 to 136.20.30.254136.20.30.255254
32136.20.31.0/24136.20.31.1 to 136.20.31.254136.20.31.255254
33136.20.32.0/24136.20.32.1 to 136.20.32.254136.20.32.255254
34136.20.33.0/24136.20.33.1 to 136.20.33.254136.20.33.255254
35136.20.34.0/24136.20.34.1 to 136.20.34.254136.20.34.255254
36136.20.35.0/24136.20.35.1 to 136.20.35.254136.20.35.255254
37136.20.36.0/24136.20.36.1 to 136.20.36.254136.20.36.255254
38136.20.37.0/24136.20.37.1 to 136.20.37.254136.20.37.255254
39136.20.38.0/24136.20.38.1 to 136.20.38.254136.20.38.255254
40136.20.39.0/24136.20.39.1 to 136.20.39.254136.20.39.255254
41136.20.40.0/24136.20.40.1 to 136.20.40.254136.20.40.255254
42136.20.41.0/24136.20.41.1 to 136.20.41.254136.20.41.255254
43136.20.42.0/24136.20.42.1 to 136.20.42.254136.20.42.255254
44136.20.43.0/24136.20.43.1 to 136.20.43.254136.20.43.255254
45136.20.44.0/24136.20.44.1 to 136.20.44.254136.20.44.255254
46136.20.45.0/24136.20.45.1 to 136.20.45.254136.20.45.255254
47136.20.46.0/24136.20.46.1 to 136.20.46.254136.20.46.255254
48136.20.47.0/24136.20.47.1 to 136.20.47.254136.20.47.255254
49136.20.48.0/24136.20.48.1 to 136.20.48.254136.20.48.255254
50136.20.49.0/24136.20.49.1 to 136.20.49.254136.20.49.255254
51136.20.50.0/24136.20.50.1 to 136.20.50.254136.20.50.255254
52136.20.51.0/24136.20.51.1 to 136.20.51.254136.20.51.255254
53136.20.52.0/24136.20.52.1 to 136.20.52.254136.20.52.255254
54136.20.53.0/24136.20.53.1 to 136.20.53.254136.20.53.255254
55136.20.54.0/24136.20.54.1 to 136.20.54.254136.20.54.255254
56136.20.55.0/24136.20.55.1 to 136.20.55.254136.20.55.255254
57136.20.56.0/24136.20.56.1 to 136.20.56.254136.20.56.255254
58136.20.57.0/24136.20.57.1 to 136.20.57.254136.20.57.255254
59136.20.58.0/24136.20.58.1 to 136.20.58.254136.20.58.255254
60136.20.59.0/24136.20.59.1 to 136.20.59.254136.20.59.255254
61136.20.60.0/24136.20.60.1 to 136.20.60.254136.20.60.255254
62136.20.61.0/24136.20.61.1 to 136.20.61.254136.20.61.255254
63136.20.62.0/24136.20.62.1 to 136.20.62.254136.20.62.255254
64136.20.63.0/24136.20.63.1 to 136.20.63.254136.20.63.255254
65136.20.64.0/24136.20.64.1 to 136.20.64.254136.20.64.255254
66136.20.65.0/24136.20.65.1 to 136.20.65.254136.20.65.255254
67136.20.66.0/24136.20.66.1 to 136.20.66.254136.20.66.255254
68136.20.67.0/24136.20.67.1 to 136.20.67.254136.20.67.255254
69136.20.68.0/24136.20.68.1 to 136.20.68.254136.20.68.255254
70136.20.69.0/24136.20.69.1 to 136.20.69.254136.20.69.255254
71136.20.70.0/24136.20.70.1 to 136.20.70.254136.20.70.255254
72136.20.71.0/24136.20.71.1 to 136.20.71.254136.20.71.255254
73136.20.72.0/24136.20.72.1 to 136.20.72.254136.20.72.255254
74136.20.73.0/24136.20.73.1 to 136.20.73.254136.20.73.255254
75136.20.74.0/24136.20.74.1 to 136.20.74.254136.20.74.255254
76136.20.75.0/24136.20.75.1 to 136.20.75.254136.20.75.255254
77136.20.76.0/24136.20.76.1 to 136.20.76.254136.20.76.255254
78136.20.77.0/24136.20.77.1 to 136.20.77.254136.20.77.255254
79136.20.78.0/24136.20.78.1 to 136.20.78.254136.20.78.255254
80136.20.79.0/24136.20.79.1 to 136.20.79.254136.20.79.255254
81136.20.80.0/24136.20.80.1 to 136.20.80.254136.20.80.255254
82136.20.81.0/24136.20.81.1 to 136.20.81.254136.20.81.255254
83136.20.82.0/24136.20.82.1 to 136.20.82.254136.20.82.255254
84136.20.83.0/24136.20.83.1 to 136.20.83.254136.20.83.255254
85136.20.84.0/24136.20.84.1 to 136.20.84.254136.20.84.255254
86136.20.85.0/24136.20.85.1 to 136.20.85.254136.20.85.255254
87136.20.86.0/24136.20.86.1 to 136.20.86.254136.20.86.255254
88136.20.87.0/24136.20.87.1 to 136.20.87.254136.20.87.255254
89136.20.88.0/24136.20.88.1 to 136.20.88.254136.20.88.255254
90136.20.89.0/24136.20.89.1 to 136.20.89.254136.20.89.255254
91136.20.90.0/24136.20.90.1 to 136.20.90.254136.20.90.255254
92136.20.91.0/24136.20.91.1 to 136.20.91.254136.20.91.255254
93136.20.92.0/24136.20.92.1 to 136.20.92.254136.20.92.255254
94136.20.93.0/24136.20.93.1 to 136.20.93.254136.20.93.255254
95136.20.94.0/24136.20.94.1 to 136.20.94.254136.20.94.255254
96136.20.95.0/24136.20.95.1 to 136.20.95.254136.20.95.255254
97136.20.96.0/24136.20.96.1 to 136.20.96.254136.20.96.255254
98136.20.97.0/24136.20.97.1 to 136.20.97.254136.20.97.255254
99136.20.98.0/24136.20.98.1 to 136.20.98.254136.20.98.255254
100136.20.99.0/24136.20.99.1 to 136.20.99.254136.20.99.255254
101136.20.100.0/24136.20.100.1 to 136.20.100.254136.20.100.255254
102136.20.101.0/24136.20.101.1 to 136.20.101.254136.20.101.255254
103136.20.102.0/24136.20.102.1 to 136.20.102.254136.20.102.255254
104136.20.103.0/24136.20.103.1 to 136.20.103.254136.20.103.255254
105136.20.104.0/24136.20.104.1 to 136.20.104.254136.20.104.255254
106136.20.105.0/24136.20.105.1 to 136.20.105.254136.20.105.255254
107136.20.106.0/24136.20.106.1 to 136.20.106.254136.20.106.255254
108136.20.107.0/24136.20.107.1 to 136.20.107.254136.20.107.255254
109136.20.108.0/24136.20.108.1 to 136.20.108.254136.20.108.255254
110136.20.109.0/24136.20.109.1 to 136.20.109.254136.20.109.255254
111136.20.110.0/24136.20.110.1 to 136.20.110.254136.20.110.255254
112136.20.111.0/24136.20.111.1 to 136.20.111.254136.20.111.255254
113136.20.112.0/24136.20.112.1 to 136.20.112.254136.20.112.255254
114136.20.113.0/24136.20.113.1 to 136.20.113.254136.20.113.255254
115136.20.114.0/24136.20.114.1 to 136.20.114.254136.20.114.255254
116136.20.115.0/24136.20.115.1 to 136.20.115.254136.20.115.255254
117136.20.116.0/24136.20.116.1 to 136.20.116.254136.20.116.255254
118136.20.117.0/24136.20.117.1 to 136.20.117.254136.20.117.255254
119136.20.118.0/24136.20.118.1 to 136.20.118.254136.20.118.255254
120136.20.119.0/24136.20.119.1 to 136.20.119.254136.20.119.255254
121136.20.120.0/24136.20.120.1 to 136.20.120.254136.20.120.255254
122136.20.121.0/24136.20.121.1 to 136.20.121.254136.20.121.255254
123136.20.122.0/24136.20.122.1 to 136.20.122.254136.20.122.255254
124136.20.123.0/24136.20.123.1 to 136.20.123.254136.20.123.255254
125136.20.124.0/24136.20.124.1 to 136.20.124.254136.20.124.255254
126136.20.125.0/24136.20.125.1 to 136.20.125.254136.20.125.255254
127136.20.126.0/24136.20.126.1 to 136.20.126.254136.20.126.255254
128136.20.127.0/24136.20.127.1 to 136.20.127.254136.20.127.255254

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.