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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.

Network239.196.72.0/21
Usable hosts2,046
Subnet mask255.255.248.0
Addresses2,048
Network address
239.196.72.0
Broadcast address
239.196.79.255
First usable
239.196.72.1
Last usable
239.196.79.254
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
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex EFC44800 · Integer 4022618112 to 4022620159
Reverse DNS zones
72.196.239.in-addr.arpa
73.196.239.in-addr.arpa
74.196.239.in-addr.arpa
75.196.239.in-addr.arpa
76.196.239.in-addr.arpa
77.196.239.in-addr.arpa
78.196.239.in-addr.arpa
79.196.239.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
Address11101111.11000100.01001000.00000000239.196.72.0
Subnet mask11111111.11111111.11111000.00000000255.255.248.0
Network11101111.11000100.01001000.00000000239.196.72.0
Broadcast11101111.11000100.01001111.11111111239.196.79.255
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)

239.196.72.0/21 makes 128 subnets of /28.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1239.196.72.0/28239.196.72.1 to 239.196.72.14239.196.72.1514
2239.196.72.16/28239.196.72.17 to 239.196.72.30239.196.72.3114
3239.196.72.32/28239.196.72.33 to 239.196.72.46239.196.72.4714
4239.196.72.48/28239.196.72.49 to 239.196.72.62239.196.72.6314
5239.196.72.64/28239.196.72.65 to 239.196.72.78239.196.72.7914
6239.196.72.80/28239.196.72.81 to 239.196.72.94239.196.72.9514
7239.196.72.96/28239.196.72.97 to 239.196.72.110239.196.72.11114
8239.196.72.112/28239.196.72.113 to 239.196.72.126239.196.72.12714
9239.196.72.128/28239.196.72.129 to 239.196.72.142239.196.72.14314
10239.196.72.144/28239.196.72.145 to 239.196.72.158239.196.72.15914
11239.196.72.160/28239.196.72.161 to 239.196.72.174239.196.72.17514
12239.196.72.176/28239.196.72.177 to 239.196.72.190239.196.72.19114
13239.196.72.192/28239.196.72.193 to 239.196.72.206239.196.72.20714
14239.196.72.208/28239.196.72.209 to 239.196.72.222239.196.72.22314
15239.196.72.224/28239.196.72.225 to 239.196.72.238239.196.72.23914
16239.196.72.240/28239.196.72.241 to 239.196.72.254239.196.72.25514
17239.196.73.0/28239.196.73.1 to 239.196.73.14239.196.73.1514
18239.196.73.16/28239.196.73.17 to 239.196.73.30239.196.73.3114
19239.196.73.32/28239.196.73.33 to 239.196.73.46239.196.73.4714
20239.196.73.48/28239.196.73.49 to 239.196.73.62239.196.73.6314
21239.196.73.64/28239.196.73.65 to 239.196.73.78239.196.73.7914
22239.196.73.80/28239.196.73.81 to 239.196.73.94239.196.73.9514
23239.196.73.96/28239.196.73.97 to 239.196.73.110239.196.73.11114
24239.196.73.112/28239.196.73.113 to 239.196.73.126239.196.73.12714
25239.196.73.128/28239.196.73.129 to 239.196.73.142239.196.73.14314
26239.196.73.144/28239.196.73.145 to 239.196.73.158239.196.73.15914
27239.196.73.160/28239.196.73.161 to 239.196.73.174239.196.73.17514
28239.196.73.176/28239.196.73.177 to 239.196.73.190239.196.73.19114
29239.196.73.192/28239.196.73.193 to 239.196.73.206239.196.73.20714
30239.196.73.208/28239.196.73.209 to 239.196.73.222239.196.73.22314
31239.196.73.224/28239.196.73.225 to 239.196.73.238239.196.73.23914
32239.196.73.240/28239.196.73.241 to 239.196.73.254239.196.73.25514
33239.196.74.0/28239.196.74.1 to 239.196.74.14239.196.74.1514
34239.196.74.16/28239.196.74.17 to 239.196.74.30239.196.74.3114
35239.196.74.32/28239.196.74.33 to 239.196.74.46239.196.74.4714
36239.196.74.48/28239.196.74.49 to 239.196.74.62239.196.74.6314
37239.196.74.64/28239.196.74.65 to 239.196.74.78239.196.74.7914
38239.196.74.80/28239.196.74.81 to 239.196.74.94239.196.74.9514
39239.196.74.96/28239.196.74.97 to 239.196.74.110239.196.74.11114
40239.196.74.112/28239.196.74.113 to 239.196.74.126239.196.74.12714
41239.196.74.128/28239.196.74.129 to 239.196.74.142239.196.74.14314
42239.196.74.144/28239.196.74.145 to 239.196.74.158239.196.74.15914
43239.196.74.160/28239.196.74.161 to 239.196.74.174239.196.74.17514
44239.196.74.176/28239.196.74.177 to 239.196.74.190239.196.74.19114
45239.196.74.192/28239.196.74.193 to 239.196.74.206239.196.74.20714
46239.196.74.208/28239.196.74.209 to 239.196.74.222239.196.74.22314
47239.196.74.224/28239.196.74.225 to 239.196.74.238239.196.74.23914
48239.196.74.240/28239.196.74.241 to 239.196.74.254239.196.74.25514
49239.196.75.0/28239.196.75.1 to 239.196.75.14239.196.75.1514
50239.196.75.16/28239.196.75.17 to 239.196.75.30239.196.75.3114
51239.196.75.32/28239.196.75.33 to 239.196.75.46239.196.75.4714
52239.196.75.48/28239.196.75.49 to 239.196.75.62239.196.75.6314
53239.196.75.64/28239.196.75.65 to 239.196.75.78239.196.75.7914
54239.196.75.80/28239.196.75.81 to 239.196.75.94239.196.75.9514
55239.196.75.96/28239.196.75.97 to 239.196.75.110239.196.75.11114
56239.196.75.112/28239.196.75.113 to 239.196.75.126239.196.75.12714
57239.196.75.128/28239.196.75.129 to 239.196.75.142239.196.75.14314
58239.196.75.144/28239.196.75.145 to 239.196.75.158239.196.75.15914
59239.196.75.160/28239.196.75.161 to 239.196.75.174239.196.75.17514
60239.196.75.176/28239.196.75.177 to 239.196.75.190239.196.75.19114
61239.196.75.192/28239.196.75.193 to 239.196.75.206239.196.75.20714
62239.196.75.208/28239.196.75.209 to 239.196.75.222239.196.75.22314
63239.196.75.224/28239.196.75.225 to 239.196.75.238239.196.75.23914
64239.196.75.240/28239.196.75.241 to 239.196.75.254239.196.75.25514
65239.196.76.0/28239.196.76.1 to 239.196.76.14239.196.76.1514
66239.196.76.16/28239.196.76.17 to 239.196.76.30239.196.76.3114
67239.196.76.32/28239.196.76.33 to 239.196.76.46239.196.76.4714
68239.196.76.48/28239.196.76.49 to 239.196.76.62239.196.76.6314
69239.196.76.64/28239.196.76.65 to 239.196.76.78239.196.76.7914
70239.196.76.80/28239.196.76.81 to 239.196.76.94239.196.76.9514
71239.196.76.96/28239.196.76.97 to 239.196.76.110239.196.76.11114
72239.196.76.112/28239.196.76.113 to 239.196.76.126239.196.76.12714
73239.196.76.128/28239.196.76.129 to 239.196.76.142239.196.76.14314
74239.196.76.144/28239.196.76.145 to 239.196.76.158239.196.76.15914
75239.196.76.160/28239.196.76.161 to 239.196.76.174239.196.76.17514
76239.196.76.176/28239.196.76.177 to 239.196.76.190239.196.76.19114
77239.196.76.192/28239.196.76.193 to 239.196.76.206239.196.76.20714
78239.196.76.208/28239.196.76.209 to 239.196.76.222239.196.76.22314
79239.196.76.224/28239.196.76.225 to 239.196.76.238239.196.76.23914
80239.196.76.240/28239.196.76.241 to 239.196.76.254239.196.76.25514
81239.196.77.0/28239.196.77.1 to 239.196.77.14239.196.77.1514
82239.196.77.16/28239.196.77.17 to 239.196.77.30239.196.77.3114
83239.196.77.32/28239.196.77.33 to 239.196.77.46239.196.77.4714
84239.196.77.48/28239.196.77.49 to 239.196.77.62239.196.77.6314
85239.196.77.64/28239.196.77.65 to 239.196.77.78239.196.77.7914
86239.196.77.80/28239.196.77.81 to 239.196.77.94239.196.77.9514
87239.196.77.96/28239.196.77.97 to 239.196.77.110239.196.77.11114
88239.196.77.112/28239.196.77.113 to 239.196.77.126239.196.77.12714
89239.196.77.128/28239.196.77.129 to 239.196.77.142239.196.77.14314
90239.196.77.144/28239.196.77.145 to 239.196.77.158239.196.77.15914
91239.196.77.160/28239.196.77.161 to 239.196.77.174239.196.77.17514
92239.196.77.176/28239.196.77.177 to 239.196.77.190239.196.77.19114
93239.196.77.192/28239.196.77.193 to 239.196.77.206239.196.77.20714
94239.196.77.208/28239.196.77.209 to 239.196.77.222239.196.77.22314
95239.196.77.224/28239.196.77.225 to 239.196.77.238239.196.77.23914
96239.196.77.240/28239.196.77.241 to 239.196.77.254239.196.77.25514
97239.196.78.0/28239.196.78.1 to 239.196.78.14239.196.78.1514
98239.196.78.16/28239.196.78.17 to 239.196.78.30239.196.78.3114
99239.196.78.32/28239.196.78.33 to 239.196.78.46239.196.78.4714
100239.196.78.48/28239.196.78.49 to 239.196.78.62239.196.78.6314
101239.196.78.64/28239.196.78.65 to 239.196.78.78239.196.78.7914
102239.196.78.80/28239.196.78.81 to 239.196.78.94239.196.78.9514
103239.196.78.96/28239.196.78.97 to 239.196.78.110239.196.78.11114
104239.196.78.112/28239.196.78.113 to 239.196.78.126239.196.78.12714
105239.196.78.128/28239.196.78.129 to 239.196.78.142239.196.78.14314
106239.196.78.144/28239.196.78.145 to 239.196.78.158239.196.78.15914
107239.196.78.160/28239.196.78.161 to 239.196.78.174239.196.78.17514
108239.196.78.176/28239.196.78.177 to 239.196.78.190239.196.78.19114
109239.196.78.192/28239.196.78.193 to 239.196.78.206239.196.78.20714
110239.196.78.208/28239.196.78.209 to 239.196.78.222239.196.78.22314
111239.196.78.224/28239.196.78.225 to 239.196.78.238239.196.78.23914
112239.196.78.240/28239.196.78.241 to 239.196.78.254239.196.78.25514
113239.196.79.0/28239.196.79.1 to 239.196.79.14239.196.79.1514
114239.196.79.16/28239.196.79.17 to 239.196.79.30239.196.79.3114
115239.196.79.32/28239.196.79.33 to 239.196.79.46239.196.79.4714
116239.196.79.48/28239.196.79.49 to 239.196.79.62239.196.79.6314
117239.196.79.64/28239.196.79.65 to 239.196.79.78239.196.79.7914
118239.196.79.80/28239.196.79.81 to 239.196.79.94239.196.79.9514
119239.196.79.96/28239.196.79.97 to 239.196.79.110239.196.79.11114
120239.196.79.112/28239.196.79.113 to 239.196.79.126239.196.79.12714
121239.196.79.128/28239.196.79.129 to 239.196.79.142239.196.79.14314
122239.196.79.144/28239.196.79.145 to 239.196.79.158239.196.79.15914
123239.196.79.160/28239.196.79.161 to 239.196.79.174239.196.79.17514
124239.196.79.176/28239.196.79.177 to 239.196.79.190239.196.79.19114
125239.196.79.192/28239.196.79.193 to 239.196.79.206239.196.79.20714
126239.196.79.208/28239.196.79.209 to 239.196.79.222239.196.79.22314
127239.196.79.224/28239.196.79.225 to 239.196.79.238239.196.79.23914
128239.196.79.240/28239.196.79.241 to 239.196.79.254239.196.79.25514

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.