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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.

Network6.167.0.0/21
Usable hosts2,046
Subnet mask255.255.248.0
Addresses2,048
Network address
6.167.0.0
Broadcast address
6.167.7.255
First usable
6.167.0.1
Last usable
6.167.7.254
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 06A70000 · Integer 111607808 to 111609855
Reverse DNS zones
0.167.6.in-addr.arpa
1.167.6.in-addr.arpa
2.167.6.in-addr.arpa
3.167.6.in-addr.arpa
4.167.6.in-addr.arpa
5.167.6.in-addr.arpa
6.167.6.in-addr.arpa
7.167.6.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
Address00000110.10100111.00000000.000000006.167.0.0
Subnet mask11111111.11111111.11111000.00000000255.255.248.0
Network00000110.10100111.00000000.000000006.167.0.0
Broadcast00000110.10100111.00000111.111111116.167.7.255
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)

6.167.0.0/21 makes 128 subnets of /28.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
16.167.0.0/286.167.0.1 to 6.167.0.146.167.0.1514
26.167.0.16/286.167.0.17 to 6.167.0.306.167.0.3114
36.167.0.32/286.167.0.33 to 6.167.0.466.167.0.4714
46.167.0.48/286.167.0.49 to 6.167.0.626.167.0.6314
56.167.0.64/286.167.0.65 to 6.167.0.786.167.0.7914
66.167.0.80/286.167.0.81 to 6.167.0.946.167.0.9514
76.167.0.96/286.167.0.97 to 6.167.0.1106.167.0.11114
86.167.0.112/286.167.0.113 to 6.167.0.1266.167.0.12714
96.167.0.128/286.167.0.129 to 6.167.0.1426.167.0.14314
106.167.0.144/286.167.0.145 to 6.167.0.1586.167.0.15914
116.167.0.160/286.167.0.161 to 6.167.0.1746.167.0.17514
126.167.0.176/286.167.0.177 to 6.167.0.1906.167.0.19114
136.167.0.192/286.167.0.193 to 6.167.0.2066.167.0.20714
146.167.0.208/286.167.0.209 to 6.167.0.2226.167.0.22314
156.167.0.224/286.167.0.225 to 6.167.0.2386.167.0.23914
166.167.0.240/286.167.0.241 to 6.167.0.2546.167.0.25514
176.167.1.0/286.167.1.1 to 6.167.1.146.167.1.1514
186.167.1.16/286.167.1.17 to 6.167.1.306.167.1.3114
196.167.1.32/286.167.1.33 to 6.167.1.466.167.1.4714
206.167.1.48/286.167.1.49 to 6.167.1.626.167.1.6314
216.167.1.64/286.167.1.65 to 6.167.1.786.167.1.7914
226.167.1.80/286.167.1.81 to 6.167.1.946.167.1.9514
236.167.1.96/286.167.1.97 to 6.167.1.1106.167.1.11114
246.167.1.112/286.167.1.113 to 6.167.1.1266.167.1.12714
256.167.1.128/286.167.1.129 to 6.167.1.1426.167.1.14314
266.167.1.144/286.167.1.145 to 6.167.1.1586.167.1.15914
276.167.1.160/286.167.1.161 to 6.167.1.1746.167.1.17514
286.167.1.176/286.167.1.177 to 6.167.1.1906.167.1.19114
296.167.1.192/286.167.1.193 to 6.167.1.2066.167.1.20714
306.167.1.208/286.167.1.209 to 6.167.1.2226.167.1.22314
316.167.1.224/286.167.1.225 to 6.167.1.2386.167.1.23914
326.167.1.240/286.167.1.241 to 6.167.1.2546.167.1.25514
336.167.2.0/286.167.2.1 to 6.167.2.146.167.2.1514
346.167.2.16/286.167.2.17 to 6.167.2.306.167.2.3114
356.167.2.32/286.167.2.33 to 6.167.2.466.167.2.4714
366.167.2.48/286.167.2.49 to 6.167.2.626.167.2.6314
376.167.2.64/286.167.2.65 to 6.167.2.786.167.2.7914
386.167.2.80/286.167.2.81 to 6.167.2.946.167.2.9514
396.167.2.96/286.167.2.97 to 6.167.2.1106.167.2.11114
406.167.2.112/286.167.2.113 to 6.167.2.1266.167.2.12714
416.167.2.128/286.167.2.129 to 6.167.2.1426.167.2.14314
426.167.2.144/286.167.2.145 to 6.167.2.1586.167.2.15914
436.167.2.160/286.167.2.161 to 6.167.2.1746.167.2.17514
446.167.2.176/286.167.2.177 to 6.167.2.1906.167.2.19114
456.167.2.192/286.167.2.193 to 6.167.2.2066.167.2.20714
466.167.2.208/286.167.2.209 to 6.167.2.2226.167.2.22314
476.167.2.224/286.167.2.225 to 6.167.2.2386.167.2.23914
486.167.2.240/286.167.2.241 to 6.167.2.2546.167.2.25514
496.167.3.0/286.167.3.1 to 6.167.3.146.167.3.1514
506.167.3.16/286.167.3.17 to 6.167.3.306.167.3.3114
516.167.3.32/286.167.3.33 to 6.167.3.466.167.3.4714
526.167.3.48/286.167.3.49 to 6.167.3.626.167.3.6314
536.167.3.64/286.167.3.65 to 6.167.3.786.167.3.7914
546.167.3.80/286.167.3.81 to 6.167.3.946.167.3.9514
556.167.3.96/286.167.3.97 to 6.167.3.1106.167.3.11114
566.167.3.112/286.167.3.113 to 6.167.3.1266.167.3.12714
576.167.3.128/286.167.3.129 to 6.167.3.1426.167.3.14314
586.167.3.144/286.167.3.145 to 6.167.3.1586.167.3.15914
596.167.3.160/286.167.3.161 to 6.167.3.1746.167.3.17514
606.167.3.176/286.167.3.177 to 6.167.3.1906.167.3.19114
616.167.3.192/286.167.3.193 to 6.167.3.2066.167.3.20714
626.167.3.208/286.167.3.209 to 6.167.3.2226.167.3.22314
636.167.3.224/286.167.3.225 to 6.167.3.2386.167.3.23914
646.167.3.240/286.167.3.241 to 6.167.3.2546.167.3.25514
656.167.4.0/286.167.4.1 to 6.167.4.146.167.4.1514
666.167.4.16/286.167.4.17 to 6.167.4.306.167.4.3114
676.167.4.32/286.167.4.33 to 6.167.4.466.167.4.4714
686.167.4.48/286.167.4.49 to 6.167.4.626.167.4.6314
696.167.4.64/286.167.4.65 to 6.167.4.786.167.4.7914
706.167.4.80/286.167.4.81 to 6.167.4.946.167.4.9514
716.167.4.96/286.167.4.97 to 6.167.4.1106.167.4.11114
726.167.4.112/286.167.4.113 to 6.167.4.1266.167.4.12714
736.167.4.128/286.167.4.129 to 6.167.4.1426.167.4.14314
746.167.4.144/286.167.4.145 to 6.167.4.1586.167.4.15914
756.167.4.160/286.167.4.161 to 6.167.4.1746.167.4.17514
766.167.4.176/286.167.4.177 to 6.167.4.1906.167.4.19114
776.167.4.192/286.167.4.193 to 6.167.4.2066.167.4.20714
786.167.4.208/286.167.4.209 to 6.167.4.2226.167.4.22314
796.167.4.224/286.167.4.225 to 6.167.4.2386.167.4.23914
806.167.4.240/286.167.4.241 to 6.167.4.2546.167.4.25514
816.167.5.0/286.167.5.1 to 6.167.5.146.167.5.1514
826.167.5.16/286.167.5.17 to 6.167.5.306.167.5.3114
836.167.5.32/286.167.5.33 to 6.167.5.466.167.5.4714
846.167.5.48/286.167.5.49 to 6.167.5.626.167.5.6314
856.167.5.64/286.167.5.65 to 6.167.5.786.167.5.7914
866.167.5.80/286.167.5.81 to 6.167.5.946.167.5.9514
876.167.5.96/286.167.5.97 to 6.167.5.1106.167.5.11114
886.167.5.112/286.167.5.113 to 6.167.5.1266.167.5.12714
896.167.5.128/286.167.5.129 to 6.167.5.1426.167.5.14314
906.167.5.144/286.167.5.145 to 6.167.5.1586.167.5.15914
916.167.5.160/286.167.5.161 to 6.167.5.1746.167.5.17514
926.167.5.176/286.167.5.177 to 6.167.5.1906.167.5.19114
936.167.5.192/286.167.5.193 to 6.167.5.2066.167.5.20714
946.167.5.208/286.167.5.209 to 6.167.5.2226.167.5.22314
956.167.5.224/286.167.5.225 to 6.167.5.2386.167.5.23914
966.167.5.240/286.167.5.241 to 6.167.5.2546.167.5.25514
976.167.6.0/286.167.6.1 to 6.167.6.146.167.6.1514
986.167.6.16/286.167.6.17 to 6.167.6.306.167.6.3114
996.167.6.32/286.167.6.33 to 6.167.6.466.167.6.4714
1006.167.6.48/286.167.6.49 to 6.167.6.626.167.6.6314
1016.167.6.64/286.167.6.65 to 6.167.6.786.167.6.7914
1026.167.6.80/286.167.6.81 to 6.167.6.946.167.6.9514
1036.167.6.96/286.167.6.97 to 6.167.6.1106.167.6.11114
1046.167.6.112/286.167.6.113 to 6.167.6.1266.167.6.12714
1056.167.6.128/286.167.6.129 to 6.167.6.1426.167.6.14314
1066.167.6.144/286.167.6.145 to 6.167.6.1586.167.6.15914
1076.167.6.160/286.167.6.161 to 6.167.6.1746.167.6.17514
1086.167.6.176/286.167.6.177 to 6.167.6.1906.167.6.19114
1096.167.6.192/286.167.6.193 to 6.167.6.2066.167.6.20714
1106.167.6.208/286.167.6.209 to 6.167.6.2226.167.6.22314
1116.167.6.224/286.167.6.225 to 6.167.6.2386.167.6.23914
1126.167.6.240/286.167.6.241 to 6.167.6.2546.167.6.25514
1136.167.7.0/286.167.7.1 to 6.167.7.146.167.7.1514
1146.167.7.16/286.167.7.17 to 6.167.7.306.167.7.3114
1156.167.7.32/286.167.7.33 to 6.167.7.466.167.7.4714
1166.167.7.48/286.167.7.49 to 6.167.7.626.167.7.6314
1176.167.7.64/286.167.7.65 to 6.167.7.786.167.7.7914
1186.167.7.80/286.167.7.81 to 6.167.7.946.167.7.9514
1196.167.7.96/286.167.7.97 to 6.167.7.1106.167.7.11114
1206.167.7.112/286.167.7.113 to 6.167.7.1266.167.7.12714
1216.167.7.128/286.167.7.129 to 6.167.7.1426.167.7.14314
1226.167.7.144/286.167.7.145 to 6.167.7.1586.167.7.15914
1236.167.7.160/286.167.7.161 to 6.167.7.1746.167.7.17514
1246.167.7.176/286.167.7.177 to 6.167.7.1906.167.7.19114
1256.167.7.192/286.167.7.193 to 6.167.7.2066.167.7.20714
1266.167.7.208/286.167.7.209 to 6.167.7.2226.167.7.22314
1276.167.7.224/286.167.7.225 to 6.167.7.2386.167.7.23914
1286.167.7.240/286.167.7.241 to 6.167.7.2546.167.7.25514

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.