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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.

Network9.136.72.0/21
Usable hosts2,046
Subnet mask255.255.248.0
Addresses2,048
Network address
9.136.72.0
Broadcast address
9.136.79.255
First usable
9.136.72.1
Last usable
9.136.79.254
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 09884800 · Integer 159926272 to 159928319
Reverse DNS zones
72.136.9.in-addr.arpa
73.136.9.in-addr.arpa
74.136.9.in-addr.arpa
75.136.9.in-addr.arpa
76.136.9.in-addr.arpa
77.136.9.in-addr.arpa
78.136.9.in-addr.arpa
79.136.9.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
Address00001001.10001000.01001000.000000009.136.72.0
Subnet mask11111111.11111111.11111000.00000000255.255.248.0
Network00001001.10001000.01001000.000000009.136.72.0
Broadcast00001001.10001000.01001111.111111119.136.79.255
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)

9.136.72.0/21 makes 128 subnets of /28.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
19.136.72.0/289.136.72.1 to 9.136.72.149.136.72.1514
29.136.72.16/289.136.72.17 to 9.136.72.309.136.72.3114
39.136.72.32/289.136.72.33 to 9.136.72.469.136.72.4714
49.136.72.48/289.136.72.49 to 9.136.72.629.136.72.6314
59.136.72.64/289.136.72.65 to 9.136.72.789.136.72.7914
69.136.72.80/289.136.72.81 to 9.136.72.949.136.72.9514
79.136.72.96/289.136.72.97 to 9.136.72.1109.136.72.11114
89.136.72.112/289.136.72.113 to 9.136.72.1269.136.72.12714
99.136.72.128/289.136.72.129 to 9.136.72.1429.136.72.14314
109.136.72.144/289.136.72.145 to 9.136.72.1589.136.72.15914
119.136.72.160/289.136.72.161 to 9.136.72.1749.136.72.17514
129.136.72.176/289.136.72.177 to 9.136.72.1909.136.72.19114
139.136.72.192/289.136.72.193 to 9.136.72.2069.136.72.20714
149.136.72.208/289.136.72.209 to 9.136.72.2229.136.72.22314
159.136.72.224/289.136.72.225 to 9.136.72.2389.136.72.23914
169.136.72.240/289.136.72.241 to 9.136.72.2549.136.72.25514
179.136.73.0/289.136.73.1 to 9.136.73.149.136.73.1514
189.136.73.16/289.136.73.17 to 9.136.73.309.136.73.3114
199.136.73.32/289.136.73.33 to 9.136.73.469.136.73.4714
209.136.73.48/289.136.73.49 to 9.136.73.629.136.73.6314
219.136.73.64/289.136.73.65 to 9.136.73.789.136.73.7914
229.136.73.80/289.136.73.81 to 9.136.73.949.136.73.9514
239.136.73.96/289.136.73.97 to 9.136.73.1109.136.73.11114
249.136.73.112/289.136.73.113 to 9.136.73.1269.136.73.12714
259.136.73.128/289.136.73.129 to 9.136.73.1429.136.73.14314
269.136.73.144/289.136.73.145 to 9.136.73.1589.136.73.15914
279.136.73.160/289.136.73.161 to 9.136.73.1749.136.73.17514
289.136.73.176/289.136.73.177 to 9.136.73.1909.136.73.19114
299.136.73.192/289.136.73.193 to 9.136.73.2069.136.73.20714
309.136.73.208/289.136.73.209 to 9.136.73.2229.136.73.22314
319.136.73.224/289.136.73.225 to 9.136.73.2389.136.73.23914
329.136.73.240/289.136.73.241 to 9.136.73.2549.136.73.25514
339.136.74.0/289.136.74.1 to 9.136.74.149.136.74.1514
349.136.74.16/289.136.74.17 to 9.136.74.309.136.74.3114
359.136.74.32/289.136.74.33 to 9.136.74.469.136.74.4714
369.136.74.48/289.136.74.49 to 9.136.74.629.136.74.6314
379.136.74.64/289.136.74.65 to 9.136.74.789.136.74.7914
389.136.74.80/289.136.74.81 to 9.136.74.949.136.74.9514
399.136.74.96/289.136.74.97 to 9.136.74.1109.136.74.11114
409.136.74.112/289.136.74.113 to 9.136.74.1269.136.74.12714
419.136.74.128/289.136.74.129 to 9.136.74.1429.136.74.14314
429.136.74.144/289.136.74.145 to 9.136.74.1589.136.74.15914
439.136.74.160/289.136.74.161 to 9.136.74.1749.136.74.17514
449.136.74.176/289.136.74.177 to 9.136.74.1909.136.74.19114
459.136.74.192/289.136.74.193 to 9.136.74.2069.136.74.20714
469.136.74.208/289.136.74.209 to 9.136.74.2229.136.74.22314
479.136.74.224/289.136.74.225 to 9.136.74.2389.136.74.23914
489.136.74.240/289.136.74.241 to 9.136.74.2549.136.74.25514
499.136.75.0/289.136.75.1 to 9.136.75.149.136.75.1514
509.136.75.16/289.136.75.17 to 9.136.75.309.136.75.3114
519.136.75.32/289.136.75.33 to 9.136.75.469.136.75.4714
529.136.75.48/289.136.75.49 to 9.136.75.629.136.75.6314
539.136.75.64/289.136.75.65 to 9.136.75.789.136.75.7914
549.136.75.80/289.136.75.81 to 9.136.75.949.136.75.9514
559.136.75.96/289.136.75.97 to 9.136.75.1109.136.75.11114
569.136.75.112/289.136.75.113 to 9.136.75.1269.136.75.12714
579.136.75.128/289.136.75.129 to 9.136.75.1429.136.75.14314
589.136.75.144/289.136.75.145 to 9.136.75.1589.136.75.15914
599.136.75.160/289.136.75.161 to 9.136.75.1749.136.75.17514
609.136.75.176/289.136.75.177 to 9.136.75.1909.136.75.19114
619.136.75.192/289.136.75.193 to 9.136.75.2069.136.75.20714
629.136.75.208/289.136.75.209 to 9.136.75.2229.136.75.22314
639.136.75.224/289.136.75.225 to 9.136.75.2389.136.75.23914
649.136.75.240/289.136.75.241 to 9.136.75.2549.136.75.25514
659.136.76.0/289.136.76.1 to 9.136.76.149.136.76.1514
669.136.76.16/289.136.76.17 to 9.136.76.309.136.76.3114
679.136.76.32/289.136.76.33 to 9.136.76.469.136.76.4714
689.136.76.48/289.136.76.49 to 9.136.76.629.136.76.6314
699.136.76.64/289.136.76.65 to 9.136.76.789.136.76.7914
709.136.76.80/289.136.76.81 to 9.136.76.949.136.76.9514
719.136.76.96/289.136.76.97 to 9.136.76.1109.136.76.11114
729.136.76.112/289.136.76.113 to 9.136.76.1269.136.76.12714
739.136.76.128/289.136.76.129 to 9.136.76.1429.136.76.14314
749.136.76.144/289.136.76.145 to 9.136.76.1589.136.76.15914
759.136.76.160/289.136.76.161 to 9.136.76.1749.136.76.17514
769.136.76.176/289.136.76.177 to 9.136.76.1909.136.76.19114
779.136.76.192/289.136.76.193 to 9.136.76.2069.136.76.20714
789.136.76.208/289.136.76.209 to 9.136.76.2229.136.76.22314
799.136.76.224/289.136.76.225 to 9.136.76.2389.136.76.23914
809.136.76.240/289.136.76.241 to 9.136.76.2549.136.76.25514
819.136.77.0/289.136.77.1 to 9.136.77.149.136.77.1514
829.136.77.16/289.136.77.17 to 9.136.77.309.136.77.3114
839.136.77.32/289.136.77.33 to 9.136.77.469.136.77.4714
849.136.77.48/289.136.77.49 to 9.136.77.629.136.77.6314
859.136.77.64/289.136.77.65 to 9.136.77.789.136.77.7914
869.136.77.80/289.136.77.81 to 9.136.77.949.136.77.9514
879.136.77.96/289.136.77.97 to 9.136.77.1109.136.77.11114
889.136.77.112/289.136.77.113 to 9.136.77.1269.136.77.12714
899.136.77.128/289.136.77.129 to 9.136.77.1429.136.77.14314
909.136.77.144/289.136.77.145 to 9.136.77.1589.136.77.15914
919.136.77.160/289.136.77.161 to 9.136.77.1749.136.77.17514
929.136.77.176/289.136.77.177 to 9.136.77.1909.136.77.19114
939.136.77.192/289.136.77.193 to 9.136.77.2069.136.77.20714
949.136.77.208/289.136.77.209 to 9.136.77.2229.136.77.22314
959.136.77.224/289.136.77.225 to 9.136.77.2389.136.77.23914
969.136.77.240/289.136.77.241 to 9.136.77.2549.136.77.25514
979.136.78.0/289.136.78.1 to 9.136.78.149.136.78.1514
989.136.78.16/289.136.78.17 to 9.136.78.309.136.78.3114
999.136.78.32/289.136.78.33 to 9.136.78.469.136.78.4714
1009.136.78.48/289.136.78.49 to 9.136.78.629.136.78.6314
1019.136.78.64/289.136.78.65 to 9.136.78.789.136.78.7914
1029.136.78.80/289.136.78.81 to 9.136.78.949.136.78.9514
1039.136.78.96/289.136.78.97 to 9.136.78.1109.136.78.11114
1049.136.78.112/289.136.78.113 to 9.136.78.1269.136.78.12714
1059.136.78.128/289.136.78.129 to 9.136.78.1429.136.78.14314
1069.136.78.144/289.136.78.145 to 9.136.78.1589.136.78.15914
1079.136.78.160/289.136.78.161 to 9.136.78.1749.136.78.17514
1089.136.78.176/289.136.78.177 to 9.136.78.1909.136.78.19114
1099.136.78.192/289.136.78.193 to 9.136.78.2069.136.78.20714
1109.136.78.208/289.136.78.209 to 9.136.78.2229.136.78.22314
1119.136.78.224/289.136.78.225 to 9.136.78.2389.136.78.23914
1129.136.78.240/289.136.78.241 to 9.136.78.2549.136.78.25514
1139.136.79.0/289.136.79.1 to 9.136.79.149.136.79.1514
1149.136.79.16/289.136.79.17 to 9.136.79.309.136.79.3114
1159.136.79.32/289.136.79.33 to 9.136.79.469.136.79.4714
1169.136.79.48/289.136.79.49 to 9.136.79.629.136.79.6314
1179.136.79.64/289.136.79.65 to 9.136.79.789.136.79.7914
1189.136.79.80/289.136.79.81 to 9.136.79.949.136.79.9514
1199.136.79.96/289.136.79.97 to 9.136.79.1109.136.79.11114
1209.136.79.112/289.136.79.113 to 9.136.79.1269.136.79.12714
1219.136.79.128/289.136.79.129 to 9.136.79.1429.136.79.14314
1229.136.79.144/289.136.79.145 to 9.136.79.1589.136.79.15914
1239.136.79.160/289.136.79.161 to 9.136.79.1749.136.79.17514
1249.136.79.176/289.136.79.177 to 9.136.79.1909.136.79.19114
1259.136.79.192/289.136.79.193 to 9.136.79.2069.136.79.20714
1269.136.79.208/289.136.79.209 to 9.136.79.2229.136.79.22314
1279.136.79.224/289.136.79.225 to 9.136.79.2389.136.79.23914
1289.136.79.240/289.136.79.241 to 9.136.79.2549.136.79.25514

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.