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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.

Network191.45.0.0/17
Usable hosts32,766
Subnet mask255.255.128.0
Addresses32,768
Network address
191.45.0.0
Broadcast address
191.45.127.255
First usable
191.45.0.1
Last usable
191.45.127.254
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 BF2D0000 · Integer 3207397376 to 3207430143
Reverse DNS zones
0.45.191.in-addr.arpa
1.45.191.in-addr.arpa
2.45.191.in-addr.arpa
3.45.191.in-addr.arpa
4.45.191.in-addr.arpa
5.45.191.in-addr.arpa
6.45.191.in-addr.arpa
7.45.191.in-addr.arpa
8.45.191.in-addr.arpa
9.45.191.in-addr.arpa
10.45.191.in-addr.arpa
11.45.191.in-addr.arpa
12.45.191.in-addr.arpa
13.45.191.in-addr.arpa
14.45.191.in-addr.arpa
15.45.191.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
Address10111111.00101101.00000000.00000000191.45.0.0
Subnet mask11111111.11111111.10000000.00000000255.255.128.0
Network10111111.00101101.00000000.00000000191.45.0.0
Broadcast10111111.00101101.01111111.11111111191.45.127.255
Split into smaller subnets/23
/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)

191.45.0.0/17 makes 64 subnets of /23.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1191.45.0.0/23191.45.0.1 to 191.45.1.254191.45.1.255510
2191.45.2.0/23191.45.2.1 to 191.45.3.254191.45.3.255510
3191.45.4.0/23191.45.4.1 to 191.45.5.254191.45.5.255510
4191.45.6.0/23191.45.6.1 to 191.45.7.254191.45.7.255510
5191.45.8.0/23191.45.8.1 to 191.45.9.254191.45.9.255510
6191.45.10.0/23191.45.10.1 to 191.45.11.254191.45.11.255510
7191.45.12.0/23191.45.12.1 to 191.45.13.254191.45.13.255510
8191.45.14.0/23191.45.14.1 to 191.45.15.254191.45.15.255510
9191.45.16.0/23191.45.16.1 to 191.45.17.254191.45.17.255510
10191.45.18.0/23191.45.18.1 to 191.45.19.254191.45.19.255510
11191.45.20.0/23191.45.20.1 to 191.45.21.254191.45.21.255510
12191.45.22.0/23191.45.22.1 to 191.45.23.254191.45.23.255510
13191.45.24.0/23191.45.24.1 to 191.45.25.254191.45.25.255510
14191.45.26.0/23191.45.26.1 to 191.45.27.254191.45.27.255510
15191.45.28.0/23191.45.28.1 to 191.45.29.254191.45.29.255510
16191.45.30.0/23191.45.30.1 to 191.45.31.254191.45.31.255510
17191.45.32.0/23191.45.32.1 to 191.45.33.254191.45.33.255510
18191.45.34.0/23191.45.34.1 to 191.45.35.254191.45.35.255510
19191.45.36.0/23191.45.36.1 to 191.45.37.254191.45.37.255510
20191.45.38.0/23191.45.38.1 to 191.45.39.254191.45.39.255510
21191.45.40.0/23191.45.40.1 to 191.45.41.254191.45.41.255510
22191.45.42.0/23191.45.42.1 to 191.45.43.254191.45.43.255510
23191.45.44.0/23191.45.44.1 to 191.45.45.254191.45.45.255510
24191.45.46.0/23191.45.46.1 to 191.45.47.254191.45.47.255510
25191.45.48.0/23191.45.48.1 to 191.45.49.254191.45.49.255510
26191.45.50.0/23191.45.50.1 to 191.45.51.254191.45.51.255510
27191.45.52.0/23191.45.52.1 to 191.45.53.254191.45.53.255510
28191.45.54.0/23191.45.54.1 to 191.45.55.254191.45.55.255510
29191.45.56.0/23191.45.56.1 to 191.45.57.254191.45.57.255510
30191.45.58.0/23191.45.58.1 to 191.45.59.254191.45.59.255510
31191.45.60.0/23191.45.60.1 to 191.45.61.254191.45.61.255510
32191.45.62.0/23191.45.62.1 to 191.45.63.254191.45.63.255510
33191.45.64.0/23191.45.64.1 to 191.45.65.254191.45.65.255510
34191.45.66.0/23191.45.66.1 to 191.45.67.254191.45.67.255510
35191.45.68.0/23191.45.68.1 to 191.45.69.254191.45.69.255510
36191.45.70.0/23191.45.70.1 to 191.45.71.254191.45.71.255510
37191.45.72.0/23191.45.72.1 to 191.45.73.254191.45.73.255510
38191.45.74.0/23191.45.74.1 to 191.45.75.254191.45.75.255510
39191.45.76.0/23191.45.76.1 to 191.45.77.254191.45.77.255510
40191.45.78.0/23191.45.78.1 to 191.45.79.254191.45.79.255510
41191.45.80.0/23191.45.80.1 to 191.45.81.254191.45.81.255510
42191.45.82.0/23191.45.82.1 to 191.45.83.254191.45.83.255510
43191.45.84.0/23191.45.84.1 to 191.45.85.254191.45.85.255510
44191.45.86.0/23191.45.86.1 to 191.45.87.254191.45.87.255510
45191.45.88.0/23191.45.88.1 to 191.45.89.254191.45.89.255510
46191.45.90.0/23191.45.90.1 to 191.45.91.254191.45.91.255510
47191.45.92.0/23191.45.92.1 to 191.45.93.254191.45.93.255510
48191.45.94.0/23191.45.94.1 to 191.45.95.254191.45.95.255510
49191.45.96.0/23191.45.96.1 to 191.45.97.254191.45.97.255510
50191.45.98.0/23191.45.98.1 to 191.45.99.254191.45.99.255510
51191.45.100.0/23191.45.100.1 to 191.45.101.254191.45.101.255510
52191.45.102.0/23191.45.102.1 to 191.45.103.254191.45.103.255510
53191.45.104.0/23191.45.104.1 to 191.45.105.254191.45.105.255510
54191.45.106.0/23191.45.106.1 to 191.45.107.254191.45.107.255510
55191.45.108.0/23191.45.108.1 to 191.45.109.254191.45.109.255510
56191.45.110.0/23191.45.110.1 to 191.45.111.254191.45.111.255510
57191.45.112.0/23191.45.112.1 to 191.45.113.254191.45.113.255510
58191.45.114.0/23191.45.114.1 to 191.45.115.254191.45.115.255510
59191.45.116.0/23191.45.116.1 to 191.45.117.254191.45.117.255510
60191.45.118.0/23191.45.118.1 to 191.45.119.254191.45.119.255510
61191.45.120.0/23191.45.120.1 to 191.45.121.254191.45.121.255510
62191.45.122.0/23191.45.122.1 to 191.45.123.254191.45.123.255510
63191.45.124.0/23191.45.124.1 to 191.45.125.254191.45.125.255510
64191.45.126.0/23191.45.126.1 to 191.45.127.254191.45.127.255510

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.