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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.

Network231.52.232.0/21
Usable hosts2,046
Subnet mask255.255.248.0
Addresses2,048
Network address
231.52.232.0
Broadcast address
231.52.239.255
First usable
231.52.232.1
Last usable
231.52.239.254
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
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex E734E800 · Integer 3879004160 to 3879006207
Reverse DNS zones
232.52.231.in-addr.arpa
233.52.231.in-addr.arpa
234.52.231.in-addr.arpa
235.52.231.in-addr.arpa
236.52.231.in-addr.arpa
237.52.231.in-addr.arpa
238.52.231.in-addr.arpa
239.52.231.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
Address11100111.00110100.11101000.00000000231.52.232.0
Subnet mask11111111.11111111.11111000.00000000255.255.248.0
Network11100111.00110100.11101000.00000000231.52.232.0
Broadcast11100111.00110100.11101111.11111111231.52.239.255
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)

231.52.232.0/21 makes 128 subnets of /28.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1231.52.232.0/28231.52.232.1 to 231.52.232.14231.52.232.1514
2231.52.232.16/28231.52.232.17 to 231.52.232.30231.52.232.3114
3231.52.232.32/28231.52.232.33 to 231.52.232.46231.52.232.4714
4231.52.232.48/28231.52.232.49 to 231.52.232.62231.52.232.6314
5231.52.232.64/28231.52.232.65 to 231.52.232.78231.52.232.7914
6231.52.232.80/28231.52.232.81 to 231.52.232.94231.52.232.9514
7231.52.232.96/28231.52.232.97 to 231.52.232.110231.52.232.11114
8231.52.232.112/28231.52.232.113 to 231.52.232.126231.52.232.12714
9231.52.232.128/28231.52.232.129 to 231.52.232.142231.52.232.14314
10231.52.232.144/28231.52.232.145 to 231.52.232.158231.52.232.15914
11231.52.232.160/28231.52.232.161 to 231.52.232.174231.52.232.17514
12231.52.232.176/28231.52.232.177 to 231.52.232.190231.52.232.19114
13231.52.232.192/28231.52.232.193 to 231.52.232.206231.52.232.20714
14231.52.232.208/28231.52.232.209 to 231.52.232.222231.52.232.22314
15231.52.232.224/28231.52.232.225 to 231.52.232.238231.52.232.23914
16231.52.232.240/28231.52.232.241 to 231.52.232.254231.52.232.25514
17231.52.233.0/28231.52.233.1 to 231.52.233.14231.52.233.1514
18231.52.233.16/28231.52.233.17 to 231.52.233.30231.52.233.3114
19231.52.233.32/28231.52.233.33 to 231.52.233.46231.52.233.4714
20231.52.233.48/28231.52.233.49 to 231.52.233.62231.52.233.6314
21231.52.233.64/28231.52.233.65 to 231.52.233.78231.52.233.7914
22231.52.233.80/28231.52.233.81 to 231.52.233.94231.52.233.9514
23231.52.233.96/28231.52.233.97 to 231.52.233.110231.52.233.11114
24231.52.233.112/28231.52.233.113 to 231.52.233.126231.52.233.12714
25231.52.233.128/28231.52.233.129 to 231.52.233.142231.52.233.14314
26231.52.233.144/28231.52.233.145 to 231.52.233.158231.52.233.15914
27231.52.233.160/28231.52.233.161 to 231.52.233.174231.52.233.17514
28231.52.233.176/28231.52.233.177 to 231.52.233.190231.52.233.19114
29231.52.233.192/28231.52.233.193 to 231.52.233.206231.52.233.20714
30231.52.233.208/28231.52.233.209 to 231.52.233.222231.52.233.22314
31231.52.233.224/28231.52.233.225 to 231.52.233.238231.52.233.23914
32231.52.233.240/28231.52.233.241 to 231.52.233.254231.52.233.25514
33231.52.234.0/28231.52.234.1 to 231.52.234.14231.52.234.1514
34231.52.234.16/28231.52.234.17 to 231.52.234.30231.52.234.3114
35231.52.234.32/28231.52.234.33 to 231.52.234.46231.52.234.4714
36231.52.234.48/28231.52.234.49 to 231.52.234.62231.52.234.6314
37231.52.234.64/28231.52.234.65 to 231.52.234.78231.52.234.7914
38231.52.234.80/28231.52.234.81 to 231.52.234.94231.52.234.9514
39231.52.234.96/28231.52.234.97 to 231.52.234.110231.52.234.11114
40231.52.234.112/28231.52.234.113 to 231.52.234.126231.52.234.12714
41231.52.234.128/28231.52.234.129 to 231.52.234.142231.52.234.14314
42231.52.234.144/28231.52.234.145 to 231.52.234.158231.52.234.15914
43231.52.234.160/28231.52.234.161 to 231.52.234.174231.52.234.17514
44231.52.234.176/28231.52.234.177 to 231.52.234.190231.52.234.19114
45231.52.234.192/28231.52.234.193 to 231.52.234.206231.52.234.20714
46231.52.234.208/28231.52.234.209 to 231.52.234.222231.52.234.22314
47231.52.234.224/28231.52.234.225 to 231.52.234.238231.52.234.23914
48231.52.234.240/28231.52.234.241 to 231.52.234.254231.52.234.25514
49231.52.235.0/28231.52.235.1 to 231.52.235.14231.52.235.1514
50231.52.235.16/28231.52.235.17 to 231.52.235.30231.52.235.3114
51231.52.235.32/28231.52.235.33 to 231.52.235.46231.52.235.4714
52231.52.235.48/28231.52.235.49 to 231.52.235.62231.52.235.6314
53231.52.235.64/28231.52.235.65 to 231.52.235.78231.52.235.7914
54231.52.235.80/28231.52.235.81 to 231.52.235.94231.52.235.9514
55231.52.235.96/28231.52.235.97 to 231.52.235.110231.52.235.11114
56231.52.235.112/28231.52.235.113 to 231.52.235.126231.52.235.12714
57231.52.235.128/28231.52.235.129 to 231.52.235.142231.52.235.14314
58231.52.235.144/28231.52.235.145 to 231.52.235.158231.52.235.15914
59231.52.235.160/28231.52.235.161 to 231.52.235.174231.52.235.17514
60231.52.235.176/28231.52.235.177 to 231.52.235.190231.52.235.19114
61231.52.235.192/28231.52.235.193 to 231.52.235.206231.52.235.20714
62231.52.235.208/28231.52.235.209 to 231.52.235.222231.52.235.22314
63231.52.235.224/28231.52.235.225 to 231.52.235.238231.52.235.23914
64231.52.235.240/28231.52.235.241 to 231.52.235.254231.52.235.25514
65231.52.236.0/28231.52.236.1 to 231.52.236.14231.52.236.1514
66231.52.236.16/28231.52.236.17 to 231.52.236.30231.52.236.3114
67231.52.236.32/28231.52.236.33 to 231.52.236.46231.52.236.4714
68231.52.236.48/28231.52.236.49 to 231.52.236.62231.52.236.6314
69231.52.236.64/28231.52.236.65 to 231.52.236.78231.52.236.7914
70231.52.236.80/28231.52.236.81 to 231.52.236.94231.52.236.9514
71231.52.236.96/28231.52.236.97 to 231.52.236.110231.52.236.11114
72231.52.236.112/28231.52.236.113 to 231.52.236.126231.52.236.12714
73231.52.236.128/28231.52.236.129 to 231.52.236.142231.52.236.14314
74231.52.236.144/28231.52.236.145 to 231.52.236.158231.52.236.15914
75231.52.236.160/28231.52.236.161 to 231.52.236.174231.52.236.17514
76231.52.236.176/28231.52.236.177 to 231.52.236.190231.52.236.19114
77231.52.236.192/28231.52.236.193 to 231.52.236.206231.52.236.20714
78231.52.236.208/28231.52.236.209 to 231.52.236.222231.52.236.22314
79231.52.236.224/28231.52.236.225 to 231.52.236.238231.52.236.23914
80231.52.236.240/28231.52.236.241 to 231.52.236.254231.52.236.25514
81231.52.237.0/28231.52.237.1 to 231.52.237.14231.52.237.1514
82231.52.237.16/28231.52.237.17 to 231.52.237.30231.52.237.3114
83231.52.237.32/28231.52.237.33 to 231.52.237.46231.52.237.4714
84231.52.237.48/28231.52.237.49 to 231.52.237.62231.52.237.6314
85231.52.237.64/28231.52.237.65 to 231.52.237.78231.52.237.7914
86231.52.237.80/28231.52.237.81 to 231.52.237.94231.52.237.9514
87231.52.237.96/28231.52.237.97 to 231.52.237.110231.52.237.11114
88231.52.237.112/28231.52.237.113 to 231.52.237.126231.52.237.12714
89231.52.237.128/28231.52.237.129 to 231.52.237.142231.52.237.14314
90231.52.237.144/28231.52.237.145 to 231.52.237.158231.52.237.15914
91231.52.237.160/28231.52.237.161 to 231.52.237.174231.52.237.17514
92231.52.237.176/28231.52.237.177 to 231.52.237.190231.52.237.19114
93231.52.237.192/28231.52.237.193 to 231.52.237.206231.52.237.20714
94231.52.237.208/28231.52.237.209 to 231.52.237.222231.52.237.22314
95231.52.237.224/28231.52.237.225 to 231.52.237.238231.52.237.23914
96231.52.237.240/28231.52.237.241 to 231.52.237.254231.52.237.25514
97231.52.238.0/28231.52.238.1 to 231.52.238.14231.52.238.1514
98231.52.238.16/28231.52.238.17 to 231.52.238.30231.52.238.3114
99231.52.238.32/28231.52.238.33 to 231.52.238.46231.52.238.4714
100231.52.238.48/28231.52.238.49 to 231.52.238.62231.52.238.6314
101231.52.238.64/28231.52.238.65 to 231.52.238.78231.52.238.7914
102231.52.238.80/28231.52.238.81 to 231.52.238.94231.52.238.9514
103231.52.238.96/28231.52.238.97 to 231.52.238.110231.52.238.11114
104231.52.238.112/28231.52.238.113 to 231.52.238.126231.52.238.12714
105231.52.238.128/28231.52.238.129 to 231.52.238.142231.52.238.14314
106231.52.238.144/28231.52.238.145 to 231.52.238.158231.52.238.15914
107231.52.238.160/28231.52.238.161 to 231.52.238.174231.52.238.17514
108231.52.238.176/28231.52.238.177 to 231.52.238.190231.52.238.19114
109231.52.238.192/28231.52.238.193 to 231.52.238.206231.52.238.20714
110231.52.238.208/28231.52.238.209 to 231.52.238.222231.52.238.22314
111231.52.238.224/28231.52.238.225 to 231.52.238.238231.52.238.23914
112231.52.238.240/28231.52.238.241 to 231.52.238.254231.52.238.25514
113231.52.239.0/28231.52.239.1 to 231.52.239.14231.52.239.1514
114231.52.239.16/28231.52.239.17 to 231.52.239.30231.52.239.3114
115231.52.239.32/28231.52.239.33 to 231.52.239.46231.52.239.4714
116231.52.239.48/28231.52.239.49 to 231.52.239.62231.52.239.6314
117231.52.239.64/28231.52.239.65 to 231.52.239.78231.52.239.7914
118231.52.239.80/28231.52.239.81 to 231.52.239.94231.52.239.9514
119231.52.239.96/28231.52.239.97 to 231.52.239.110231.52.239.11114
120231.52.239.112/28231.52.239.113 to 231.52.239.126231.52.239.12714
121231.52.239.128/28231.52.239.129 to 231.52.239.142231.52.239.14314
122231.52.239.144/28231.52.239.145 to 231.52.239.158231.52.239.15914
123231.52.239.160/28231.52.239.161 to 231.52.239.174231.52.239.17514
124231.52.239.176/28231.52.239.177 to 231.52.239.190231.52.239.19114
125231.52.239.192/28231.52.239.193 to 231.52.239.206231.52.239.20714
126231.52.239.208/28231.52.239.209 to 231.52.239.222231.52.239.22314
127231.52.239.224/28231.52.239.225 to 231.52.239.238231.52.239.23914
128231.52.239.240/28231.52.239.241 to 231.52.239.254231.52.239.25514

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.