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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.

Network199.71.0.0/17
Usable hosts32,766
Subnet mask255.255.128.0
Addresses32,768
Network address
199.71.0.0
Broadcast address
199.71.127.255
First usable
199.71.0.1
Last usable
199.71.127.254
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
C (default /24)
As numbers
Hex C7470000 · Integer 3343319040 to 3343351807
Reverse DNS zones
0.71.199.in-addr.arpa
1.71.199.in-addr.arpa
2.71.199.in-addr.arpa
3.71.199.in-addr.arpa
4.71.199.in-addr.arpa
5.71.199.in-addr.arpa
6.71.199.in-addr.arpa
7.71.199.in-addr.arpa
8.71.199.in-addr.arpa
9.71.199.in-addr.arpa
10.71.199.in-addr.arpa
11.71.199.in-addr.arpa
12.71.199.in-addr.arpa
13.71.199.in-addr.arpa
14.71.199.in-addr.arpa
15.71.199.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
Address11000111.01000111.00000000.00000000199.71.0.0
Subnet mask11111111.11111111.10000000.00000000255.255.128.0
Network11000111.01000111.00000000.00000000199.71.0.0
Broadcast11000111.01000111.01111111.11111111199.71.127.255
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)

199.71.0.0/17 makes 64 subnets of /23.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1199.71.0.0/23199.71.0.1 to 199.71.1.254199.71.1.255510
2199.71.2.0/23199.71.2.1 to 199.71.3.254199.71.3.255510
3199.71.4.0/23199.71.4.1 to 199.71.5.254199.71.5.255510
4199.71.6.0/23199.71.6.1 to 199.71.7.254199.71.7.255510
5199.71.8.0/23199.71.8.1 to 199.71.9.254199.71.9.255510
6199.71.10.0/23199.71.10.1 to 199.71.11.254199.71.11.255510
7199.71.12.0/23199.71.12.1 to 199.71.13.254199.71.13.255510
8199.71.14.0/23199.71.14.1 to 199.71.15.254199.71.15.255510
9199.71.16.0/23199.71.16.1 to 199.71.17.254199.71.17.255510
10199.71.18.0/23199.71.18.1 to 199.71.19.254199.71.19.255510
11199.71.20.0/23199.71.20.1 to 199.71.21.254199.71.21.255510
12199.71.22.0/23199.71.22.1 to 199.71.23.254199.71.23.255510
13199.71.24.0/23199.71.24.1 to 199.71.25.254199.71.25.255510
14199.71.26.0/23199.71.26.1 to 199.71.27.254199.71.27.255510
15199.71.28.0/23199.71.28.1 to 199.71.29.254199.71.29.255510
16199.71.30.0/23199.71.30.1 to 199.71.31.254199.71.31.255510
17199.71.32.0/23199.71.32.1 to 199.71.33.254199.71.33.255510
18199.71.34.0/23199.71.34.1 to 199.71.35.254199.71.35.255510
19199.71.36.0/23199.71.36.1 to 199.71.37.254199.71.37.255510
20199.71.38.0/23199.71.38.1 to 199.71.39.254199.71.39.255510
21199.71.40.0/23199.71.40.1 to 199.71.41.254199.71.41.255510
22199.71.42.0/23199.71.42.1 to 199.71.43.254199.71.43.255510
23199.71.44.0/23199.71.44.1 to 199.71.45.254199.71.45.255510
24199.71.46.0/23199.71.46.1 to 199.71.47.254199.71.47.255510
25199.71.48.0/23199.71.48.1 to 199.71.49.254199.71.49.255510
26199.71.50.0/23199.71.50.1 to 199.71.51.254199.71.51.255510
27199.71.52.0/23199.71.52.1 to 199.71.53.254199.71.53.255510
28199.71.54.0/23199.71.54.1 to 199.71.55.254199.71.55.255510
29199.71.56.0/23199.71.56.1 to 199.71.57.254199.71.57.255510
30199.71.58.0/23199.71.58.1 to 199.71.59.254199.71.59.255510
31199.71.60.0/23199.71.60.1 to 199.71.61.254199.71.61.255510
32199.71.62.0/23199.71.62.1 to 199.71.63.254199.71.63.255510
33199.71.64.0/23199.71.64.1 to 199.71.65.254199.71.65.255510
34199.71.66.0/23199.71.66.1 to 199.71.67.254199.71.67.255510
35199.71.68.0/23199.71.68.1 to 199.71.69.254199.71.69.255510
36199.71.70.0/23199.71.70.1 to 199.71.71.254199.71.71.255510
37199.71.72.0/23199.71.72.1 to 199.71.73.254199.71.73.255510
38199.71.74.0/23199.71.74.1 to 199.71.75.254199.71.75.255510
39199.71.76.0/23199.71.76.1 to 199.71.77.254199.71.77.255510
40199.71.78.0/23199.71.78.1 to 199.71.79.254199.71.79.255510
41199.71.80.0/23199.71.80.1 to 199.71.81.254199.71.81.255510
42199.71.82.0/23199.71.82.1 to 199.71.83.254199.71.83.255510
43199.71.84.0/23199.71.84.1 to 199.71.85.254199.71.85.255510
44199.71.86.0/23199.71.86.1 to 199.71.87.254199.71.87.255510
45199.71.88.0/23199.71.88.1 to 199.71.89.254199.71.89.255510
46199.71.90.0/23199.71.90.1 to 199.71.91.254199.71.91.255510
47199.71.92.0/23199.71.92.1 to 199.71.93.254199.71.93.255510
48199.71.94.0/23199.71.94.1 to 199.71.95.254199.71.95.255510
49199.71.96.0/23199.71.96.1 to 199.71.97.254199.71.97.255510
50199.71.98.0/23199.71.98.1 to 199.71.99.254199.71.99.255510
51199.71.100.0/23199.71.100.1 to 199.71.101.254199.71.101.255510
52199.71.102.0/23199.71.102.1 to 199.71.103.254199.71.103.255510
53199.71.104.0/23199.71.104.1 to 199.71.105.254199.71.105.255510
54199.71.106.0/23199.71.106.1 to 199.71.107.254199.71.107.255510
55199.71.108.0/23199.71.108.1 to 199.71.109.254199.71.109.255510
56199.71.110.0/23199.71.110.1 to 199.71.111.254199.71.111.255510
57199.71.112.0/23199.71.112.1 to 199.71.113.254199.71.113.255510
58199.71.114.0/23199.71.114.1 to 199.71.115.254199.71.115.255510
59199.71.116.0/23199.71.116.1 to 199.71.117.254199.71.117.255510
60199.71.118.0/23199.71.118.1 to 199.71.119.254199.71.119.255510
61199.71.120.0/23199.71.120.1 to 199.71.121.254199.71.121.255510
62199.71.122.0/23199.71.122.1 to 199.71.123.254199.71.123.255510
63199.71.124.0/23199.71.124.1 to 199.71.125.254199.71.125.255510
64199.71.126.0/23199.71.126.1 to 199.71.127.254199.71.127.255510

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.