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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.

Network167.3.232.0/21
Usable hosts2,046
Subnet mask255.255.248.0
Addresses2,048
Network address
167.3.232.0
Broadcast address
167.3.239.255
First usable
167.3.232.1
Last usable
167.3.239.254
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
B (default /16)
As numbers
Hex A703E800 · Integer 2802051072 to 2802053119
Reverse DNS zones
232.3.167.in-addr.arpa
233.3.167.in-addr.arpa
234.3.167.in-addr.arpa
235.3.167.in-addr.arpa
236.3.167.in-addr.arpa
237.3.167.in-addr.arpa
238.3.167.in-addr.arpa
239.3.167.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
Address10100111.00000011.11101000.00000000167.3.232.0
Subnet mask11111111.11111111.11111000.00000000255.255.248.0
Network10100111.00000011.11101000.00000000167.3.232.0
Broadcast10100111.00000011.11101111.11111111167.3.239.255
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)

167.3.232.0/21 makes 128 subnets of /28.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1167.3.232.0/28167.3.232.1 to 167.3.232.14167.3.232.1514
2167.3.232.16/28167.3.232.17 to 167.3.232.30167.3.232.3114
3167.3.232.32/28167.3.232.33 to 167.3.232.46167.3.232.4714
4167.3.232.48/28167.3.232.49 to 167.3.232.62167.3.232.6314
5167.3.232.64/28167.3.232.65 to 167.3.232.78167.3.232.7914
6167.3.232.80/28167.3.232.81 to 167.3.232.94167.3.232.9514
7167.3.232.96/28167.3.232.97 to 167.3.232.110167.3.232.11114
8167.3.232.112/28167.3.232.113 to 167.3.232.126167.3.232.12714
9167.3.232.128/28167.3.232.129 to 167.3.232.142167.3.232.14314
10167.3.232.144/28167.3.232.145 to 167.3.232.158167.3.232.15914
11167.3.232.160/28167.3.232.161 to 167.3.232.174167.3.232.17514
12167.3.232.176/28167.3.232.177 to 167.3.232.190167.3.232.19114
13167.3.232.192/28167.3.232.193 to 167.3.232.206167.3.232.20714
14167.3.232.208/28167.3.232.209 to 167.3.232.222167.3.232.22314
15167.3.232.224/28167.3.232.225 to 167.3.232.238167.3.232.23914
16167.3.232.240/28167.3.232.241 to 167.3.232.254167.3.232.25514
17167.3.233.0/28167.3.233.1 to 167.3.233.14167.3.233.1514
18167.3.233.16/28167.3.233.17 to 167.3.233.30167.3.233.3114
19167.3.233.32/28167.3.233.33 to 167.3.233.46167.3.233.4714
20167.3.233.48/28167.3.233.49 to 167.3.233.62167.3.233.6314
21167.3.233.64/28167.3.233.65 to 167.3.233.78167.3.233.7914
22167.3.233.80/28167.3.233.81 to 167.3.233.94167.3.233.9514
23167.3.233.96/28167.3.233.97 to 167.3.233.110167.3.233.11114
24167.3.233.112/28167.3.233.113 to 167.3.233.126167.3.233.12714
25167.3.233.128/28167.3.233.129 to 167.3.233.142167.3.233.14314
26167.3.233.144/28167.3.233.145 to 167.3.233.158167.3.233.15914
27167.3.233.160/28167.3.233.161 to 167.3.233.174167.3.233.17514
28167.3.233.176/28167.3.233.177 to 167.3.233.190167.3.233.19114
29167.3.233.192/28167.3.233.193 to 167.3.233.206167.3.233.20714
30167.3.233.208/28167.3.233.209 to 167.3.233.222167.3.233.22314
31167.3.233.224/28167.3.233.225 to 167.3.233.238167.3.233.23914
32167.3.233.240/28167.3.233.241 to 167.3.233.254167.3.233.25514
33167.3.234.0/28167.3.234.1 to 167.3.234.14167.3.234.1514
34167.3.234.16/28167.3.234.17 to 167.3.234.30167.3.234.3114
35167.3.234.32/28167.3.234.33 to 167.3.234.46167.3.234.4714
36167.3.234.48/28167.3.234.49 to 167.3.234.62167.3.234.6314
37167.3.234.64/28167.3.234.65 to 167.3.234.78167.3.234.7914
38167.3.234.80/28167.3.234.81 to 167.3.234.94167.3.234.9514
39167.3.234.96/28167.3.234.97 to 167.3.234.110167.3.234.11114
40167.3.234.112/28167.3.234.113 to 167.3.234.126167.3.234.12714
41167.3.234.128/28167.3.234.129 to 167.3.234.142167.3.234.14314
42167.3.234.144/28167.3.234.145 to 167.3.234.158167.3.234.15914
43167.3.234.160/28167.3.234.161 to 167.3.234.174167.3.234.17514
44167.3.234.176/28167.3.234.177 to 167.3.234.190167.3.234.19114
45167.3.234.192/28167.3.234.193 to 167.3.234.206167.3.234.20714
46167.3.234.208/28167.3.234.209 to 167.3.234.222167.3.234.22314
47167.3.234.224/28167.3.234.225 to 167.3.234.238167.3.234.23914
48167.3.234.240/28167.3.234.241 to 167.3.234.254167.3.234.25514
49167.3.235.0/28167.3.235.1 to 167.3.235.14167.3.235.1514
50167.3.235.16/28167.3.235.17 to 167.3.235.30167.3.235.3114
51167.3.235.32/28167.3.235.33 to 167.3.235.46167.3.235.4714
52167.3.235.48/28167.3.235.49 to 167.3.235.62167.3.235.6314
53167.3.235.64/28167.3.235.65 to 167.3.235.78167.3.235.7914
54167.3.235.80/28167.3.235.81 to 167.3.235.94167.3.235.9514
55167.3.235.96/28167.3.235.97 to 167.3.235.110167.3.235.11114
56167.3.235.112/28167.3.235.113 to 167.3.235.126167.3.235.12714
57167.3.235.128/28167.3.235.129 to 167.3.235.142167.3.235.14314
58167.3.235.144/28167.3.235.145 to 167.3.235.158167.3.235.15914
59167.3.235.160/28167.3.235.161 to 167.3.235.174167.3.235.17514
60167.3.235.176/28167.3.235.177 to 167.3.235.190167.3.235.19114
61167.3.235.192/28167.3.235.193 to 167.3.235.206167.3.235.20714
62167.3.235.208/28167.3.235.209 to 167.3.235.222167.3.235.22314
63167.3.235.224/28167.3.235.225 to 167.3.235.238167.3.235.23914
64167.3.235.240/28167.3.235.241 to 167.3.235.254167.3.235.25514
65167.3.236.0/28167.3.236.1 to 167.3.236.14167.3.236.1514
66167.3.236.16/28167.3.236.17 to 167.3.236.30167.3.236.3114
67167.3.236.32/28167.3.236.33 to 167.3.236.46167.3.236.4714
68167.3.236.48/28167.3.236.49 to 167.3.236.62167.3.236.6314
69167.3.236.64/28167.3.236.65 to 167.3.236.78167.3.236.7914
70167.3.236.80/28167.3.236.81 to 167.3.236.94167.3.236.9514
71167.3.236.96/28167.3.236.97 to 167.3.236.110167.3.236.11114
72167.3.236.112/28167.3.236.113 to 167.3.236.126167.3.236.12714
73167.3.236.128/28167.3.236.129 to 167.3.236.142167.3.236.14314
74167.3.236.144/28167.3.236.145 to 167.3.236.158167.3.236.15914
75167.3.236.160/28167.3.236.161 to 167.3.236.174167.3.236.17514
76167.3.236.176/28167.3.236.177 to 167.3.236.190167.3.236.19114
77167.3.236.192/28167.3.236.193 to 167.3.236.206167.3.236.20714
78167.3.236.208/28167.3.236.209 to 167.3.236.222167.3.236.22314
79167.3.236.224/28167.3.236.225 to 167.3.236.238167.3.236.23914
80167.3.236.240/28167.3.236.241 to 167.3.236.254167.3.236.25514
81167.3.237.0/28167.3.237.1 to 167.3.237.14167.3.237.1514
82167.3.237.16/28167.3.237.17 to 167.3.237.30167.3.237.3114
83167.3.237.32/28167.3.237.33 to 167.3.237.46167.3.237.4714
84167.3.237.48/28167.3.237.49 to 167.3.237.62167.3.237.6314
85167.3.237.64/28167.3.237.65 to 167.3.237.78167.3.237.7914
86167.3.237.80/28167.3.237.81 to 167.3.237.94167.3.237.9514
87167.3.237.96/28167.3.237.97 to 167.3.237.110167.3.237.11114
88167.3.237.112/28167.3.237.113 to 167.3.237.126167.3.237.12714
89167.3.237.128/28167.3.237.129 to 167.3.237.142167.3.237.14314
90167.3.237.144/28167.3.237.145 to 167.3.237.158167.3.237.15914
91167.3.237.160/28167.3.237.161 to 167.3.237.174167.3.237.17514
92167.3.237.176/28167.3.237.177 to 167.3.237.190167.3.237.19114
93167.3.237.192/28167.3.237.193 to 167.3.237.206167.3.237.20714
94167.3.237.208/28167.3.237.209 to 167.3.237.222167.3.237.22314
95167.3.237.224/28167.3.237.225 to 167.3.237.238167.3.237.23914
96167.3.237.240/28167.3.237.241 to 167.3.237.254167.3.237.25514
97167.3.238.0/28167.3.238.1 to 167.3.238.14167.3.238.1514
98167.3.238.16/28167.3.238.17 to 167.3.238.30167.3.238.3114
99167.3.238.32/28167.3.238.33 to 167.3.238.46167.3.238.4714
100167.3.238.48/28167.3.238.49 to 167.3.238.62167.3.238.6314
101167.3.238.64/28167.3.238.65 to 167.3.238.78167.3.238.7914
102167.3.238.80/28167.3.238.81 to 167.3.238.94167.3.238.9514
103167.3.238.96/28167.3.238.97 to 167.3.238.110167.3.238.11114
104167.3.238.112/28167.3.238.113 to 167.3.238.126167.3.238.12714
105167.3.238.128/28167.3.238.129 to 167.3.238.142167.3.238.14314
106167.3.238.144/28167.3.238.145 to 167.3.238.158167.3.238.15914
107167.3.238.160/28167.3.238.161 to 167.3.238.174167.3.238.17514
108167.3.238.176/28167.3.238.177 to 167.3.238.190167.3.238.19114
109167.3.238.192/28167.3.238.193 to 167.3.238.206167.3.238.20714
110167.3.238.208/28167.3.238.209 to 167.3.238.222167.3.238.22314
111167.3.238.224/28167.3.238.225 to 167.3.238.238167.3.238.23914
112167.3.238.240/28167.3.238.241 to 167.3.238.254167.3.238.25514
113167.3.239.0/28167.3.239.1 to 167.3.239.14167.3.239.1514
114167.3.239.16/28167.3.239.17 to 167.3.239.30167.3.239.3114
115167.3.239.32/28167.3.239.33 to 167.3.239.46167.3.239.4714
116167.3.239.48/28167.3.239.49 to 167.3.239.62167.3.239.6314
117167.3.239.64/28167.3.239.65 to 167.3.239.78167.3.239.7914
118167.3.239.80/28167.3.239.81 to 167.3.239.94167.3.239.9514
119167.3.239.96/28167.3.239.97 to 167.3.239.110167.3.239.11114
120167.3.239.112/28167.3.239.113 to 167.3.239.126167.3.239.12714
121167.3.239.128/28167.3.239.129 to 167.3.239.142167.3.239.14314
122167.3.239.144/28167.3.239.145 to 167.3.239.158167.3.239.15914
123167.3.239.160/28167.3.239.161 to 167.3.239.174167.3.239.17514
124167.3.239.176/28167.3.239.177 to 167.3.239.190167.3.239.19114
125167.3.239.192/28167.3.239.193 to 167.3.239.206167.3.239.20714
126167.3.239.208/28167.3.239.209 to 167.3.239.222167.3.239.22314
127167.3.239.224/28167.3.239.225 to 167.3.239.238167.3.239.23914
128167.3.239.240/28167.3.239.241 to 167.3.239.254167.3.239.25514

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.