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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.

Network191.68.0.0/17
Usable hosts32,766
Subnet mask255.255.128.0
Addresses32,768
Network address
191.68.0.0
Broadcast address
191.68.127.255
First usable
191.68.0.1
Last usable
191.68.127.254
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 BF440000 · Integer 3208904704 to 3208937471
Reverse DNS zones
0.68.191.in-addr.arpa
1.68.191.in-addr.arpa
2.68.191.in-addr.arpa
3.68.191.in-addr.arpa
4.68.191.in-addr.arpa
5.68.191.in-addr.arpa
6.68.191.in-addr.arpa
7.68.191.in-addr.arpa
8.68.191.in-addr.arpa
9.68.191.in-addr.arpa
10.68.191.in-addr.arpa
11.68.191.in-addr.arpa
12.68.191.in-addr.arpa
13.68.191.in-addr.arpa
14.68.191.in-addr.arpa
15.68.191.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
Address10111111.01000100.00000000.00000000191.68.0.0
Subnet mask11111111.11111111.10000000.00000000255.255.128.0
Network10111111.01000100.00000000.00000000191.68.0.0
Broadcast10111111.01000100.01111111.11111111191.68.127.255
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)

191.68.0.0/17 makes 128 subnets of /24.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1191.68.0.0/24191.68.0.1 to 191.68.0.254191.68.0.255254
2191.68.1.0/24191.68.1.1 to 191.68.1.254191.68.1.255254
3191.68.2.0/24191.68.2.1 to 191.68.2.254191.68.2.255254
4191.68.3.0/24191.68.3.1 to 191.68.3.254191.68.3.255254
5191.68.4.0/24191.68.4.1 to 191.68.4.254191.68.4.255254
6191.68.5.0/24191.68.5.1 to 191.68.5.254191.68.5.255254
7191.68.6.0/24191.68.6.1 to 191.68.6.254191.68.6.255254
8191.68.7.0/24191.68.7.1 to 191.68.7.254191.68.7.255254
9191.68.8.0/24191.68.8.1 to 191.68.8.254191.68.8.255254
10191.68.9.0/24191.68.9.1 to 191.68.9.254191.68.9.255254
11191.68.10.0/24191.68.10.1 to 191.68.10.254191.68.10.255254
12191.68.11.0/24191.68.11.1 to 191.68.11.254191.68.11.255254
13191.68.12.0/24191.68.12.1 to 191.68.12.254191.68.12.255254
14191.68.13.0/24191.68.13.1 to 191.68.13.254191.68.13.255254
15191.68.14.0/24191.68.14.1 to 191.68.14.254191.68.14.255254
16191.68.15.0/24191.68.15.1 to 191.68.15.254191.68.15.255254
17191.68.16.0/24191.68.16.1 to 191.68.16.254191.68.16.255254
18191.68.17.0/24191.68.17.1 to 191.68.17.254191.68.17.255254
19191.68.18.0/24191.68.18.1 to 191.68.18.254191.68.18.255254
20191.68.19.0/24191.68.19.1 to 191.68.19.254191.68.19.255254
21191.68.20.0/24191.68.20.1 to 191.68.20.254191.68.20.255254
22191.68.21.0/24191.68.21.1 to 191.68.21.254191.68.21.255254
23191.68.22.0/24191.68.22.1 to 191.68.22.254191.68.22.255254
24191.68.23.0/24191.68.23.1 to 191.68.23.254191.68.23.255254
25191.68.24.0/24191.68.24.1 to 191.68.24.254191.68.24.255254
26191.68.25.0/24191.68.25.1 to 191.68.25.254191.68.25.255254
27191.68.26.0/24191.68.26.1 to 191.68.26.254191.68.26.255254
28191.68.27.0/24191.68.27.1 to 191.68.27.254191.68.27.255254
29191.68.28.0/24191.68.28.1 to 191.68.28.254191.68.28.255254
30191.68.29.0/24191.68.29.1 to 191.68.29.254191.68.29.255254
31191.68.30.0/24191.68.30.1 to 191.68.30.254191.68.30.255254
32191.68.31.0/24191.68.31.1 to 191.68.31.254191.68.31.255254
33191.68.32.0/24191.68.32.1 to 191.68.32.254191.68.32.255254
34191.68.33.0/24191.68.33.1 to 191.68.33.254191.68.33.255254
35191.68.34.0/24191.68.34.1 to 191.68.34.254191.68.34.255254
36191.68.35.0/24191.68.35.1 to 191.68.35.254191.68.35.255254
37191.68.36.0/24191.68.36.1 to 191.68.36.254191.68.36.255254
38191.68.37.0/24191.68.37.1 to 191.68.37.254191.68.37.255254
39191.68.38.0/24191.68.38.1 to 191.68.38.254191.68.38.255254
40191.68.39.0/24191.68.39.1 to 191.68.39.254191.68.39.255254
41191.68.40.0/24191.68.40.1 to 191.68.40.254191.68.40.255254
42191.68.41.0/24191.68.41.1 to 191.68.41.254191.68.41.255254
43191.68.42.0/24191.68.42.1 to 191.68.42.254191.68.42.255254
44191.68.43.0/24191.68.43.1 to 191.68.43.254191.68.43.255254
45191.68.44.0/24191.68.44.1 to 191.68.44.254191.68.44.255254
46191.68.45.0/24191.68.45.1 to 191.68.45.254191.68.45.255254
47191.68.46.0/24191.68.46.1 to 191.68.46.254191.68.46.255254
48191.68.47.0/24191.68.47.1 to 191.68.47.254191.68.47.255254
49191.68.48.0/24191.68.48.1 to 191.68.48.254191.68.48.255254
50191.68.49.0/24191.68.49.1 to 191.68.49.254191.68.49.255254
51191.68.50.0/24191.68.50.1 to 191.68.50.254191.68.50.255254
52191.68.51.0/24191.68.51.1 to 191.68.51.254191.68.51.255254
53191.68.52.0/24191.68.52.1 to 191.68.52.254191.68.52.255254
54191.68.53.0/24191.68.53.1 to 191.68.53.254191.68.53.255254
55191.68.54.0/24191.68.54.1 to 191.68.54.254191.68.54.255254
56191.68.55.0/24191.68.55.1 to 191.68.55.254191.68.55.255254
57191.68.56.0/24191.68.56.1 to 191.68.56.254191.68.56.255254
58191.68.57.0/24191.68.57.1 to 191.68.57.254191.68.57.255254
59191.68.58.0/24191.68.58.1 to 191.68.58.254191.68.58.255254
60191.68.59.0/24191.68.59.1 to 191.68.59.254191.68.59.255254
61191.68.60.0/24191.68.60.1 to 191.68.60.254191.68.60.255254
62191.68.61.0/24191.68.61.1 to 191.68.61.254191.68.61.255254
63191.68.62.0/24191.68.62.1 to 191.68.62.254191.68.62.255254
64191.68.63.0/24191.68.63.1 to 191.68.63.254191.68.63.255254
65191.68.64.0/24191.68.64.1 to 191.68.64.254191.68.64.255254
66191.68.65.0/24191.68.65.1 to 191.68.65.254191.68.65.255254
67191.68.66.0/24191.68.66.1 to 191.68.66.254191.68.66.255254
68191.68.67.0/24191.68.67.1 to 191.68.67.254191.68.67.255254
69191.68.68.0/24191.68.68.1 to 191.68.68.254191.68.68.255254
70191.68.69.0/24191.68.69.1 to 191.68.69.254191.68.69.255254
71191.68.70.0/24191.68.70.1 to 191.68.70.254191.68.70.255254
72191.68.71.0/24191.68.71.1 to 191.68.71.254191.68.71.255254
73191.68.72.0/24191.68.72.1 to 191.68.72.254191.68.72.255254
74191.68.73.0/24191.68.73.1 to 191.68.73.254191.68.73.255254
75191.68.74.0/24191.68.74.1 to 191.68.74.254191.68.74.255254
76191.68.75.0/24191.68.75.1 to 191.68.75.254191.68.75.255254
77191.68.76.0/24191.68.76.1 to 191.68.76.254191.68.76.255254
78191.68.77.0/24191.68.77.1 to 191.68.77.254191.68.77.255254
79191.68.78.0/24191.68.78.1 to 191.68.78.254191.68.78.255254
80191.68.79.0/24191.68.79.1 to 191.68.79.254191.68.79.255254
81191.68.80.0/24191.68.80.1 to 191.68.80.254191.68.80.255254
82191.68.81.0/24191.68.81.1 to 191.68.81.254191.68.81.255254
83191.68.82.0/24191.68.82.1 to 191.68.82.254191.68.82.255254
84191.68.83.0/24191.68.83.1 to 191.68.83.254191.68.83.255254
85191.68.84.0/24191.68.84.1 to 191.68.84.254191.68.84.255254
86191.68.85.0/24191.68.85.1 to 191.68.85.254191.68.85.255254
87191.68.86.0/24191.68.86.1 to 191.68.86.254191.68.86.255254
88191.68.87.0/24191.68.87.1 to 191.68.87.254191.68.87.255254
89191.68.88.0/24191.68.88.1 to 191.68.88.254191.68.88.255254
90191.68.89.0/24191.68.89.1 to 191.68.89.254191.68.89.255254
91191.68.90.0/24191.68.90.1 to 191.68.90.254191.68.90.255254
92191.68.91.0/24191.68.91.1 to 191.68.91.254191.68.91.255254
93191.68.92.0/24191.68.92.1 to 191.68.92.254191.68.92.255254
94191.68.93.0/24191.68.93.1 to 191.68.93.254191.68.93.255254
95191.68.94.0/24191.68.94.1 to 191.68.94.254191.68.94.255254
96191.68.95.0/24191.68.95.1 to 191.68.95.254191.68.95.255254
97191.68.96.0/24191.68.96.1 to 191.68.96.254191.68.96.255254
98191.68.97.0/24191.68.97.1 to 191.68.97.254191.68.97.255254
99191.68.98.0/24191.68.98.1 to 191.68.98.254191.68.98.255254
100191.68.99.0/24191.68.99.1 to 191.68.99.254191.68.99.255254
101191.68.100.0/24191.68.100.1 to 191.68.100.254191.68.100.255254
102191.68.101.0/24191.68.101.1 to 191.68.101.254191.68.101.255254
103191.68.102.0/24191.68.102.1 to 191.68.102.254191.68.102.255254
104191.68.103.0/24191.68.103.1 to 191.68.103.254191.68.103.255254
105191.68.104.0/24191.68.104.1 to 191.68.104.254191.68.104.255254
106191.68.105.0/24191.68.105.1 to 191.68.105.254191.68.105.255254
107191.68.106.0/24191.68.106.1 to 191.68.106.254191.68.106.255254
108191.68.107.0/24191.68.107.1 to 191.68.107.254191.68.107.255254
109191.68.108.0/24191.68.108.1 to 191.68.108.254191.68.108.255254
110191.68.109.0/24191.68.109.1 to 191.68.109.254191.68.109.255254
111191.68.110.0/24191.68.110.1 to 191.68.110.254191.68.110.255254
112191.68.111.0/24191.68.111.1 to 191.68.111.254191.68.111.255254
113191.68.112.0/24191.68.112.1 to 191.68.112.254191.68.112.255254
114191.68.113.0/24191.68.113.1 to 191.68.113.254191.68.113.255254
115191.68.114.0/24191.68.114.1 to 191.68.114.254191.68.114.255254
116191.68.115.0/24191.68.115.1 to 191.68.115.254191.68.115.255254
117191.68.116.0/24191.68.116.1 to 191.68.116.254191.68.116.255254
118191.68.117.0/24191.68.117.1 to 191.68.117.254191.68.117.255254
119191.68.118.0/24191.68.118.1 to 191.68.118.254191.68.118.255254
120191.68.119.0/24191.68.119.1 to 191.68.119.254191.68.119.255254
121191.68.120.0/24191.68.120.1 to 191.68.120.254191.68.120.255254
122191.68.121.0/24191.68.121.1 to 191.68.121.254191.68.121.255254
123191.68.122.0/24191.68.122.1 to 191.68.122.254191.68.122.255254
124191.68.123.0/24191.68.123.1 to 191.68.123.254191.68.123.255254
125191.68.124.0/24191.68.124.1 to 191.68.124.254191.68.124.255254
126191.68.125.0/24191.68.125.1 to 191.68.125.254191.68.125.255254
127191.68.126.0/24191.68.126.1 to 191.68.126.254191.68.126.255254
128191.68.127.0/24191.68.127.1 to 191.68.127.254191.68.127.255254

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.