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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.

Network68.2.192.0/21
Usable hosts2,046
Subnet mask255.255.248.0
Addresses2,048
Network address
68.2.192.0
Broadcast address
68.2.199.255
First usable
68.2.192.1
Last usable
68.2.199.254
Usable hosts
2,046 (2,048 less the network and broadcast addresses)
Subnet mask
255.255.248.0
Wildcard mask
0.0.7.255 (Cisco ACLs, OSPF)
Prefix length
/21
Type
Public public
Old class
A (default /8)
As numbers
Hex 4402C000 · Integer 1141030912 to 1141032959
Reverse DNS zones
192.2.68.in-addr.arpa
193.2.68.in-addr.arpa
194.2.68.in-addr.arpa
195.2.68.in-addr.arpa
196.2.68.in-addr.arpa
197.2.68.in-addr.arpa
198.2.68.in-addr.arpa
199.2.68.in-addr.arpa
/21 is not on a 8-bit boundary, so it takes 8 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01000100.00000010.11000000.0000000068.2.192.0
Subnet mask11111111.11111111.11111000.00000000255.255.248.0
Network01000100.00000010.11000000.0000000068.2.192.0
Broadcast01000100.00000010.11000111.1111111168.2.199.255
Split into smaller subnets/28
/22 (2)/23 (4)/24 (8)/25 (16)/26 (32)/27 (64)/28 (128)/29 (256)/30 (512)/31 (1,024)/32 (2,048)

68.2.192.0/21 makes 128 subnets of /28.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
168.2.192.0/2868.2.192.1 to 68.2.192.1468.2.192.1514
268.2.192.16/2868.2.192.17 to 68.2.192.3068.2.192.3114
368.2.192.32/2868.2.192.33 to 68.2.192.4668.2.192.4714
468.2.192.48/2868.2.192.49 to 68.2.192.6268.2.192.6314
568.2.192.64/2868.2.192.65 to 68.2.192.7868.2.192.7914
668.2.192.80/2868.2.192.81 to 68.2.192.9468.2.192.9514
768.2.192.96/2868.2.192.97 to 68.2.192.11068.2.192.11114
868.2.192.112/2868.2.192.113 to 68.2.192.12668.2.192.12714
968.2.192.128/2868.2.192.129 to 68.2.192.14268.2.192.14314
1068.2.192.144/2868.2.192.145 to 68.2.192.15868.2.192.15914
1168.2.192.160/2868.2.192.161 to 68.2.192.17468.2.192.17514
1268.2.192.176/2868.2.192.177 to 68.2.192.19068.2.192.19114
1368.2.192.192/2868.2.192.193 to 68.2.192.20668.2.192.20714
1468.2.192.208/2868.2.192.209 to 68.2.192.22268.2.192.22314
1568.2.192.224/2868.2.192.225 to 68.2.192.23868.2.192.23914
1668.2.192.240/2868.2.192.241 to 68.2.192.25468.2.192.25514
1768.2.193.0/2868.2.193.1 to 68.2.193.1468.2.193.1514
1868.2.193.16/2868.2.193.17 to 68.2.193.3068.2.193.3114
1968.2.193.32/2868.2.193.33 to 68.2.193.4668.2.193.4714
2068.2.193.48/2868.2.193.49 to 68.2.193.6268.2.193.6314
2168.2.193.64/2868.2.193.65 to 68.2.193.7868.2.193.7914
2268.2.193.80/2868.2.193.81 to 68.2.193.9468.2.193.9514
2368.2.193.96/2868.2.193.97 to 68.2.193.11068.2.193.11114
2468.2.193.112/2868.2.193.113 to 68.2.193.12668.2.193.12714
2568.2.193.128/2868.2.193.129 to 68.2.193.14268.2.193.14314
2668.2.193.144/2868.2.193.145 to 68.2.193.15868.2.193.15914
2768.2.193.160/2868.2.193.161 to 68.2.193.17468.2.193.17514
2868.2.193.176/2868.2.193.177 to 68.2.193.19068.2.193.19114
2968.2.193.192/2868.2.193.193 to 68.2.193.20668.2.193.20714
3068.2.193.208/2868.2.193.209 to 68.2.193.22268.2.193.22314
3168.2.193.224/2868.2.193.225 to 68.2.193.23868.2.193.23914
3268.2.193.240/2868.2.193.241 to 68.2.193.25468.2.193.25514
3368.2.194.0/2868.2.194.1 to 68.2.194.1468.2.194.1514
3468.2.194.16/2868.2.194.17 to 68.2.194.3068.2.194.3114
3568.2.194.32/2868.2.194.33 to 68.2.194.4668.2.194.4714
3668.2.194.48/2868.2.194.49 to 68.2.194.6268.2.194.6314
3768.2.194.64/2868.2.194.65 to 68.2.194.7868.2.194.7914
3868.2.194.80/2868.2.194.81 to 68.2.194.9468.2.194.9514
3968.2.194.96/2868.2.194.97 to 68.2.194.11068.2.194.11114
4068.2.194.112/2868.2.194.113 to 68.2.194.12668.2.194.12714
4168.2.194.128/2868.2.194.129 to 68.2.194.14268.2.194.14314
4268.2.194.144/2868.2.194.145 to 68.2.194.15868.2.194.15914
4368.2.194.160/2868.2.194.161 to 68.2.194.17468.2.194.17514
4468.2.194.176/2868.2.194.177 to 68.2.194.19068.2.194.19114
4568.2.194.192/2868.2.194.193 to 68.2.194.20668.2.194.20714
4668.2.194.208/2868.2.194.209 to 68.2.194.22268.2.194.22314
4768.2.194.224/2868.2.194.225 to 68.2.194.23868.2.194.23914
4868.2.194.240/2868.2.194.241 to 68.2.194.25468.2.194.25514
4968.2.195.0/2868.2.195.1 to 68.2.195.1468.2.195.1514
5068.2.195.16/2868.2.195.17 to 68.2.195.3068.2.195.3114
5168.2.195.32/2868.2.195.33 to 68.2.195.4668.2.195.4714
5268.2.195.48/2868.2.195.49 to 68.2.195.6268.2.195.6314
5368.2.195.64/2868.2.195.65 to 68.2.195.7868.2.195.7914
5468.2.195.80/2868.2.195.81 to 68.2.195.9468.2.195.9514
5568.2.195.96/2868.2.195.97 to 68.2.195.11068.2.195.11114
5668.2.195.112/2868.2.195.113 to 68.2.195.12668.2.195.12714
5768.2.195.128/2868.2.195.129 to 68.2.195.14268.2.195.14314
5868.2.195.144/2868.2.195.145 to 68.2.195.15868.2.195.15914
5968.2.195.160/2868.2.195.161 to 68.2.195.17468.2.195.17514
6068.2.195.176/2868.2.195.177 to 68.2.195.19068.2.195.19114
6168.2.195.192/2868.2.195.193 to 68.2.195.20668.2.195.20714
6268.2.195.208/2868.2.195.209 to 68.2.195.22268.2.195.22314
6368.2.195.224/2868.2.195.225 to 68.2.195.23868.2.195.23914
6468.2.195.240/2868.2.195.241 to 68.2.195.25468.2.195.25514
6568.2.196.0/2868.2.196.1 to 68.2.196.1468.2.196.1514
6668.2.196.16/2868.2.196.17 to 68.2.196.3068.2.196.3114
6768.2.196.32/2868.2.196.33 to 68.2.196.4668.2.196.4714
6868.2.196.48/2868.2.196.49 to 68.2.196.6268.2.196.6314
6968.2.196.64/2868.2.196.65 to 68.2.196.7868.2.196.7914
7068.2.196.80/2868.2.196.81 to 68.2.196.9468.2.196.9514
7168.2.196.96/2868.2.196.97 to 68.2.196.11068.2.196.11114
7268.2.196.112/2868.2.196.113 to 68.2.196.12668.2.196.12714
7368.2.196.128/2868.2.196.129 to 68.2.196.14268.2.196.14314
7468.2.196.144/2868.2.196.145 to 68.2.196.15868.2.196.15914
7568.2.196.160/2868.2.196.161 to 68.2.196.17468.2.196.17514
7668.2.196.176/2868.2.196.177 to 68.2.196.19068.2.196.19114
7768.2.196.192/2868.2.196.193 to 68.2.196.20668.2.196.20714
7868.2.196.208/2868.2.196.209 to 68.2.196.22268.2.196.22314
7968.2.196.224/2868.2.196.225 to 68.2.196.23868.2.196.23914
8068.2.196.240/2868.2.196.241 to 68.2.196.25468.2.196.25514
8168.2.197.0/2868.2.197.1 to 68.2.197.1468.2.197.1514
8268.2.197.16/2868.2.197.17 to 68.2.197.3068.2.197.3114
8368.2.197.32/2868.2.197.33 to 68.2.197.4668.2.197.4714
8468.2.197.48/2868.2.197.49 to 68.2.197.6268.2.197.6314
8568.2.197.64/2868.2.197.65 to 68.2.197.7868.2.197.7914
8668.2.197.80/2868.2.197.81 to 68.2.197.9468.2.197.9514
8768.2.197.96/2868.2.197.97 to 68.2.197.11068.2.197.11114
8868.2.197.112/2868.2.197.113 to 68.2.197.12668.2.197.12714
8968.2.197.128/2868.2.197.129 to 68.2.197.14268.2.197.14314
9068.2.197.144/2868.2.197.145 to 68.2.197.15868.2.197.15914
9168.2.197.160/2868.2.197.161 to 68.2.197.17468.2.197.17514
9268.2.197.176/2868.2.197.177 to 68.2.197.19068.2.197.19114
9368.2.197.192/2868.2.197.193 to 68.2.197.20668.2.197.20714
9468.2.197.208/2868.2.197.209 to 68.2.197.22268.2.197.22314
9568.2.197.224/2868.2.197.225 to 68.2.197.23868.2.197.23914
9668.2.197.240/2868.2.197.241 to 68.2.197.25468.2.197.25514
9768.2.198.0/2868.2.198.1 to 68.2.198.1468.2.198.1514
9868.2.198.16/2868.2.198.17 to 68.2.198.3068.2.198.3114
9968.2.198.32/2868.2.198.33 to 68.2.198.4668.2.198.4714
10068.2.198.48/2868.2.198.49 to 68.2.198.6268.2.198.6314
10168.2.198.64/2868.2.198.65 to 68.2.198.7868.2.198.7914
10268.2.198.80/2868.2.198.81 to 68.2.198.9468.2.198.9514
10368.2.198.96/2868.2.198.97 to 68.2.198.11068.2.198.11114
10468.2.198.112/2868.2.198.113 to 68.2.198.12668.2.198.12714
10568.2.198.128/2868.2.198.129 to 68.2.198.14268.2.198.14314
10668.2.198.144/2868.2.198.145 to 68.2.198.15868.2.198.15914
10768.2.198.160/2868.2.198.161 to 68.2.198.17468.2.198.17514
10868.2.198.176/2868.2.198.177 to 68.2.198.19068.2.198.19114
10968.2.198.192/2868.2.198.193 to 68.2.198.20668.2.198.20714
11068.2.198.208/2868.2.198.209 to 68.2.198.22268.2.198.22314
11168.2.198.224/2868.2.198.225 to 68.2.198.23868.2.198.23914
11268.2.198.240/2868.2.198.241 to 68.2.198.25468.2.198.25514
11368.2.199.0/2868.2.199.1 to 68.2.199.1468.2.199.1514
11468.2.199.16/2868.2.199.17 to 68.2.199.3068.2.199.3114
11568.2.199.32/2868.2.199.33 to 68.2.199.4668.2.199.4714
11668.2.199.48/2868.2.199.49 to 68.2.199.6268.2.199.6314
11768.2.199.64/2868.2.199.65 to 68.2.199.7868.2.199.7914
11868.2.199.80/2868.2.199.81 to 68.2.199.9468.2.199.9514
11968.2.199.96/2868.2.199.97 to 68.2.199.11068.2.199.11114
12068.2.199.112/2868.2.199.113 to 68.2.199.12668.2.199.12714
12168.2.199.128/2868.2.199.129 to 68.2.199.14268.2.199.14314
12268.2.199.144/2868.2.199.145 to 68.2.199.15868.2.199.15914
12368.2.199.160/2868.2.199.161 to 68.2.199.17468.2.199.17514
12468.2.199.176/2868.2.199.177 to 68.2.199.19068.2.199.19114
12568.2.199.192/2868.2.199.193 to 68.2.199.20668.2.199.20714
12668.2.199.208/2868.2.199.209 to 68.2.199.22268.2.199.22314
12768.2.199.224/2868.2.199.225 to 68.2.199.23868.2.199.23914
12868.2.199.240/2868.2.199.241 to 68.2.199.25468.2.199.25514

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.