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.

Network37.0.0.0/8

Usable hosts16,777,214

Subnet mask255.0.0.0

Addresses16,777,216

Network address: 37.0.0.0
Broadcast address: 37.255.255.255
First usable: 37.0.0.1
Last usable: 37.255.255.254
Usable hosts: 16,777,214 (16,777,216 less the network and broadcast addresses)
Subnet mask: 255.0.0.0
Wildcard mask: 0.255.255.255 (Cisco ACLs, OSPF)
Prefix length: /8
Type: Public public
Old class: A (default /8)
As numbers: Hex 25000000 · Integer 620756992 to 637534207
Reverse DNS zone: 37.in-addr.arpa

Binary

Binary view
	Binary (network bits bold, host bits grey)	Dotted
Address	`00100101..00000000.00000000.00000000`	`37.0.0.0`
Subnet mask	`11111111..00000000.00000000.00000000`	`255.0.0.0`
Network	`00100101..00000000.00000000.00000000`	`37.0.0.0`
Broadcast	`00100101..11111111.11111111.11111111`	`37.255.255.255`

Split into smaller subnets/15

/9 (2)/10 (4)/11 (8)/12 (16)/13 (32)/14 (64)/15 (128)/16 (256)/17 (512)/18 (1,024)/19 (2,048)/20 (4,096)

37.0.0.0/8 makes 128 subnets of /15.

Subnets
#	Subnet	Usable hosts range	Broadcast	Hosts
1	`37.0.0.0/15`	`37.0.0.1` to `37.1.255.254`	37.1.255.255	131,070
2	`37.2.0.0/15`	`37.2.0.1` to `37.3.255.254`	37.3.255.255	131,070
3	`37.4.0.0/15`	`37.4.0.1` to `37.5.255.254`	37.5.255.255	131,070
4	`37.6.0.0/15`	`37.6.0.1` to `37.7.255.254`	37.7.255.255	131,070
5	`37.8.0.0/15`	`37.8.0.1` to `37.9.255.254`	37.9.255.255	131,070
6	`37.10.0.0/15`	`37.10.0.1` to `37.11.255.254`	37.11.255.255	131,070
7	`37.12.0.0/15`	`37.12.0.1` to `37.13.255.254`	37.13.255.255	131,070
8	`37.14.0.0/15`	`37.14.0.1` to `37.15.255.254`	37.15.255.255	131,070
9	`37.16.0.0/15`	`37.16.0.1` to `37.17.255.254`	37.17.255.255	131,070
10	`37.18.0.0/15`	`37.18.0.1` to `37.19.255.254`	37.19.255.255	131,070
11	`37.20.0.0/15`	`37.20.0.1` to `37.21.255.254`	37.21.255.255	131,070
12	`37.22.0.0/15`	`37.22.0.1` to `37.23.255.254`	37.23.255.255	131,070
13	`37.24.0.0/15`	`37.24.0.1` to `37.25.255.254`	37.25.255.255	131,070
14	`37.26.0.0/15`	`37.26.0.1` to `37.27.255.254`	37.27.255.255	131,070
15	`37.28.0.0/15`	`37.28.0.1` to `37.29.255.254`	37.29.255.255	131,070
16	`37.30.0.0/15`	`37.30.0.1` to `37.31.255.254`	37.31.255.255	131,070
17	`37.32.0.0/15`	`37.32.0.1` to `37.33.255.254`	37.33.255.255	131,070
18	`37.34.0.0/15`	`37.34.0.1` to `37.35.255.254`	37.35.255.255	131,070
19	`37.36.0.0/15`	`37.36.0.1` to `37.37.255.254`	37.37.255.255	131,070
20	`37.38.0.0/15`	`37.38.0.1` to `37.39.255.254`	37.39.255.255	131,070
21	`37.40.0.0/15`	`37.40.0.1` to `37.41.255.254`	37.41.255.255	131,070
22	`37.42.0.0/15`	`37.42.0.1` to `37.43.255.254`	37.43.255.255	131,070
23	`37.44.0.0/15`	`37.44.0.1` to `37.45.255.254`	37.45.255.255	131,070
24	`37.46.0.0/15`	`37.46.0.1` to `37.47.255.254`	37.47.255.255	131,070
25	`37.48.0.0/15`	`37.48.0.1` to `37.49.255.254`	37.49.255.255	131,070
26	`37.50.0.0/15`	`37.50.0.1` to `37.51.255.254`	37.51.255.255	131,070
27	`37.52.0.0/15`	`37.52.0.1` to `37.53.255.254`	37.53.255.255	131,070
28	`37.54.0.0/15`	`37.54.0.1` to `37.55.255.254`	37.55.255.255	131,070
29	`37.56.0.0/15`	`37.56.0.1` to `37.57.255.254`	37.57.255.255	131,070
30	`37.58.0.0/15`	`37.58.0.1` to `37.59.255.254`	37.59.255.255	131,070
31	`37.60.0.0/15`	`37.60.0.1` to `37.61.255.254`	37.61.255.255	131,070
32	`37.62.0.0/15`	`37.62.0.1` to `37.63.255.254`	37.63.255.255	131,070
33	`37.64.0.0/15`	`37.64.0.1` to `37.65.255.254`	37.65.255.255	131,070
34	`37.66.0.0/15`	`37.66.0.1` to `37.67.255.254`	37.67.255.255	131,070
35	`37.68.0.0/15`	`37.68.0.1` to `37.69.255.254`	37.69.255.255	131,070
36	`37.70.0.0/15`	`37.70.0.1` to `37.71.255.254`	37.71.255.255	131,070
37	`37.72.0.0/15`	`37.72.0.1` to `37.73.255.254`	37.73.255.255	131,070
38	`37.74.0.0/15`	`37.74.0.1` to `37.75.255.254`	37.75.255.255	131,070
39	`37.76.0.0/15`	`37.76.0.1` to `37.77.255.254`	37.77.255.255	131,070
40	`37.78.0.0/15`	`37.78.0.1` to `37.79.255.254`	37.79.255.255	131,070
41	`37.80.0.0/15`	`37.80.0.1` to `37.81.255.254`	37.81.255.255	131,070
42	`37.82.0.0/15`	`37.82.0.1` to `37.83.255.254`	37.83.255.255	131,070
43	`37.84.0.0/15`	`37.84.0.1` to `37.85.255.254`	37.85.255.255	131,070
44	`37.86.0.0/15`	`37.86.0.1` to `37.87.255.254`	37.87.255.255	131,070
45	`37.88.0.0/15`	`37.88.0.1` to `37.89.255.254`	37.89.255.255	131,070
46	`37.90.0.0/15`	`37.90.0.1` to `37.91.255.254`	37.91.255.255	131,070
47	`37.92.0.0/15`	`37.92.0.1` to `37.93.255.254`	37.93.255.255	131,070
48	`37.94.0.0/15`	`37.94.0.1` to `37.95.255.254`	37.95.255.255	131,070
49	`37.96.0.0/15`	`37.96.0.1` to `37.97.255.254`	37.97.255.255	131,070
50	`37.98.0.0/15`	`37.98.0.1` to `37.99.255.254`	37.99.255.255	131,070
51	`37.100.0.0/15`	`37.100.0.1` to `37.101.255.254`	37.101.255.255	131,070
52	`37.102.0.0/15`	`37.102.0.1` to `37.103.255.254`	37.103.255.255	131,070
53	`37.104.0.0/15`	`37.104.0.1` to `37.105.255.254`	37.105.255.255	131,070
54	`37.106.0.0/15`	`37.106.0.1` to `37.107.255.254`	37.107.255.255	131,070
55	`37.108.0.0/15`	`37.108.0.1` to `37.109.255.254`	37.109.255.255	131,070
56	`37.110.0.0/15`	`37.110.0.1` to `37.111.255.254`	37.111.255.255	131,070
57	`37.112.0.0/15`	`37.112.0.1` to `37.113.255.254`	37.113.255.255	131,070
58	`37.114.0.0/15`	`37.114.0.1` to `37.115.255.254`	37.115.255.255	131,070
59	`37.116.0.0/15`	`37.116.0.1` to `37.117.255.254`	37.117.255.255	131,070
60	`37.118.0.0/15`	`37.118.0.1` to `37.119.255.254`	37.119.255.255	131,070
61	`37.120.0.0/15`	`37.120.0.1` to `37.121.255.254`	37.121.255.255	131,070
62	`37.122.0.0/15`	`37.122.0.1` to `37.123.255.254`	37.123.255.255	131,070
63	`37.124.0.0/15`	`37.124.0.1` to `37.125.255.254`	37.125.255.255	131,070
64	`37.126.0.0/15`	`37.126.0.1` to `37.127.255.254`	37.127.255.255	131,070
65	`37.128.0.0/15`	`37.128.0.1` to `37.129.255.254`	37.129.255.255	131,070
66	`37.130.0.0/15`	`37.130.0.1` to `37.131.255.254`	37.131.255.255	131,070
67	`37.132.0.0/15`	`37.132.0.1` to `37.133.255.254`	37.133.255.255	131,070
68	`37.134.0.0/15`	`37.134.0.1` to `37.135.255.254`	37.135.255.255	131,070
69	`37.136.0.0/15`	`37.136.0.1` to `37.137.255.254`	37.137.255.255	131,070
70	`37.138.0.0/15`	`37.138.0.1` to `37.139.255.254`	37.139.255.255	131,070
71	`37.140.0.0/15`	`37.140.0.1` to `37.141.255.254`	37.141.255.255	131,070
72	`37.142.0.0/15`	`37.142.0.1` to `37.143.255.254`	37.143.255.255	131,070
73	`37.144.0.0/15`	`37.144.0.1` to `37.145.255.254`	37.145.255.255	131,070
74	`37.146.0.0/15`	`37.146.0.1` to `37.147.255.254`	37.147.255.255	131,070
75	`37.148.0.0/15`	`37.148.0.1` to `37.149.255.254`	37.149.255.255	131,070
76	`37.150.0.0/15`	`37.150.0.1` to `37.151.255.254`	37.151.255.255	131,070
77	`37.152.0.0/15`	`37.152.0.1` to `37.153.255.254`	37.153.255.255	131,070
78	`37.154.0.0/15`	`37.154.0.1` to `37.155.255.254`	37.155.255.255	131,070
79	`37.156.0.0/15`	`37.156.0.1` to `37.157.255.254`	37.157.255.255	131,070
80	`37.158.0.0/15`	`37.158.0.1` to `37.159.255.254`	37.159.255.255	131,070
81	`37.160.0.0/15`	`37.160.0.1` to `37.161.255.254`	37.161.255.255	131,070
82	`37.162.0.0/15`	`37.162.0.1` to `37.163.255.254`	37.163.255.255	131,070
83	`37.164.0.0/15`	`37.164.0.1` to `37.165.255.254`	37.165.255.255	131,070
84	`37.166.0.0/15`	`37.166.0.1` to `37.167.255.254`	37.167.255.255	131,070
85	`37.168.0.0/15`	`37.168.0.1` to `37.169.255.254`	37.169.255.255	131,070
86	`37.170.0.0/15`	`37.170.0.1` to `37.171.255.254`	37.171.255.255	131,070
87	`37.172.0.0/15`	`37.172.0.1` to `37.173.255.254`	37.173.255.255	131,070
88	`37.174.0.0/15`	`37.174.0.1` to `37.175.255.254`	37.175.255.255	131,070
89	`37.176.0.0/15`	`37.176.0.1` to `37.177.255.254`	37.177.255.255	131,070
90	`37.178.0.0/15`	`37.178.0.1` to `37.179.255.254`	37.179.255.255	131,070
91	`37.180.0.0/15`	`37.180.0.1` to `37.181.255.254`	37.181.255.255	131,070
92	`37.182.0.0/15`	`37.182.0.1` to `37.183.255.254`	37.183.255.255	131,070
93	`37.184.0.0/15`	`37.184.0.1` to `37.185.255.254`	37.185.255.255	131,070
94	`37.186.0.0/15`	`37.186.0.1` to `37.187.255.254`	37.187.255.255	131,070
95	`37.188.0.0/15`	`37.188.0.1` to `37.189.255.254`	37.189.255.255	131,070
96	`37.190.0.0/15`	`37.190.0.1` to `37.191.255.254`	37.191.255.255	131,070
97	`37.192.0.0/15`	`37.192.0.1` to `37.193.255.254`	37.193.255.255	131,070
98	`37.194.0.0/15`	`37.194.0.1` to `37.195.255.254`	37.195.255.255	131,070
99	`37.196.0.0/15`	`37.196.0.1` to `37.197.255.254`	37.197.255.255	131,070
100	`37.198.0.0/15`	`37.198.0.1` to `37.199.255.254`	37.199.255.255	131,070
101	`37.200.0.0/15`	`37.200.0.1` to `37.201.255.254`	37.201.255.255	131,070
102	`37.202.0.0/15`	`37.202.0.1` to `37.203.255.254`	37.203.255.255	131,070
103	`37.204.0.0/15`	`37.204.0.1` to `37.205.255.254`	37.205.255.255	131,070
104	`37.206.0.0/15`	`37.206.0.1` to `37.207.255.254`	37.207.255.255	131,070
105	`37.208.0.0/15`	`37.208.0.1` to `37.209.255.254`	37.209.255.255	131,070
106	`37.210.0.0/15`	`37.210.0.1` to `37.211.255.254`	37.211.255.255	131,070
107	`37.212.0.0/15`	`37.212.0.1` to `37.213.255.254`	37.213.255.255	131,070
108	`37.214.0.0/15`	`37.214.0.1` to `37.215.255.254`	37.215.255.255	131,070
109	`37.216.0.0/15`	`37.216.0.1` to `37.217.255.254`	37.217.255.255	131,070
110	`37.218.0.0/15`	`37.218.0.1` to `37.219.255.254`	37.219.255.255	131,070
111	`37.220.0.0/15`	`37.220.0.1` to `37.221.255.254`	37.221.255.255	131,070
112	`37.222.0.0/15`	`37.222.0.1` to `37.223.255.254`	37.223.255.255	131,070
113	`37.224.0.0/15`	`37.224.0.1` to `37.225.255.254`	37.225.255.255	131,070
114	`37.226.0.0/15`	`37.226.0.1` to `37.227.255.254`	37.227.255.255	131,070
115	`37.228.0.0/15`	`37.228.0.1` to `37.229.255.254`	37.229.255.255	131,070
116	`37.230.0.0/15`	`37.230.0.1` to `37.231.255.254`	37.231.255.255	131,070
117	`37.232.0.0/15`	`37.232.0.1` to `37.233.255.254`	37.233.255.255	131,070
118	`37.234.0.0/15`	`37.234.0.1` to `37.235.255.254`	37.235.255.255	131,070
119	`37.236.0.0/15`	`37.236.0.1` to `37.237.255.254`	37.237.255.255	131,070
120	`37.238.0.0/15`	`37.238.0.1` to `37.239.255.254`	37.239.255.255	131,070
121	`37.240.0.0/15`	`37.240.0.1` to `37.241.255.254`	37.241.255.255	131,070
122	`37.242.0.0/15`	`37.242.0.1` to `37.243.255.254`	37.243.255.255	131,070
123	`37.244.0.0/15`	`37.244.0.1` to `37.245.255.254`	37.245.255.255	131,070
124	`37.246.0.0/15`	`37.246.0.1` to `37.247.255.254`	37.247.255.255	131,070
125	`37.248.0.0/15`	`37.248.0.1` to `37.249.255.254`	37.249.255.255	131,070
126	`37.250.0.0/15`	`37.250.0.1` to `37.251.255.254`	37.251.255.255	131,070
127	`37.252.0.0/15`	`37.252.0.1` to `37.253.255.254`	37.253.255.255	131,070
128	`37.254.0.0/15`	`37.254.0.1` to `37.255.255.254`	37.255.255.255	131,070

IPv4 CIDR reference (/0 to /32)

IPv4 prefix lengths
Prefix	Subnet mask	Wildcard	Addresses	Usable hosts	Size	Typical use
/0	0.0.0.0	255.255.255.255	4,294,967,296	4,294,967,294	16,777,216 × /24
/1	128.0.0.0	127.255.255.255	2,147,483,648	2,147,483,646	8,388,608 × /24
/2	192.0.0.0	63.255.255.255	1,073,741,824	1,073,741,822	4,194,304 × /24
/3	224.0.0.0	31.255.255.255	536,870,912	536,870,910	2,097,152 × /24
/4	240.0.0.0	15.255.255.255	268,435,456	268,435,454	1,048,576 × /24
/5	248.0.0.0	7.255.255.255	134,217,728	134,217,726	524,288 × /24
/6	252.0.0.0	3.255.255.255	67,108,864	67,108,862	262,144 × /24
/7	254.0.0.0	1.255.255.255	33,554,432	33,554,430	131,072 × /24
/8	255.0.0.0	0.255.255.255	16,777,216	16,777,214	65,536 × /24	Old class A; 10.0.0.0/8
/9	255.128.0.0	0.127.255.255	8,388,608	8,388,606	32,768 × /24
/10	255.192.0.0	0.63.255.255	4,194,304	4,194,302	16,384 × /24
/11	255.224.0.0	0.31.255.255	2,097,152	2,097,150	8,192 × /24
/12	255.240.0.0	0.15.255.255	1,048,576	1,048,574	4,096 × /24	172.16.0.0/12
/13	255.248.0.0	0.7.255.255	524,288	524,286	2,048 × /24
/14	255.252.0.0	0.3.255.255	262,144	262,142	1,024 × /24
/15	255.254.0.0	0.1.255.255	131,072	131,070	512 × /24
/16	255.255.0.0	0.0.255.255	65,536	65,534	256 × /24	Old class B; 192.168.0.0/16
/17	255.255.128.0	0.0.127.255	32,768	32,766	128 × /24
/18	255.255.192.0	0.0.63.255	16,384	16,382	64 × /24
/19	255.255.224.0	0.0.31.255	8,192	8,190	32 × /24
/20	255.255.240.0	0.0.15.255	4,096	4,094	16 × /24
/21	255.255.248.0	0.0.7.255	2,048	2,046	8 × /24
/22	255.255.252.0	0.0.3.255	1,024	1,022	4 × /24	Large office or guest Wi-Fi (1,022 hosts)
/23	255.255.254.0	0.0.1.255	512	510	2 × /24	Larger office LAN (510 hosts)
/24	255.255.255.0	0.0.0.255	256	254	1 × /24	Typical office LAN (old class C)
/25	255.255.255.128	0.0.0.127	128	126	1/2 of a /24	Smaller LAN or VLAN
/26	255.255.255.192	0.0.0.63	64	62	1/4 of a /24	Smaller LAN or VLAN
/27	255.255.255.224	0.0.0.31	32	30	1/8 of a /24	Small VLAN, phones, cameras
/28	255.255.255.240	0.0.0.15	16	14	1/16 of a /24	Small VLAN, phones, cameras
/29	255.255.255.248	0.0.0.7	8	6	1/32 of a /24	Small fixed public block (5 usable)
/30	255.255.255.252	0.0.0.3	4	2	1/64 of a /24	Point-to-point (old style)
/31	255.255.255.254	0.0.0.1	2	2	1/128 of a /24	Point-to-point link (RFC 3021)
/32	255.255.255.255	0.0.0.0	1	1	1/256 of a /24	One host

IPv6 prefix reference

IPv6 prefix lengths
Prefix	Addresses	/64 LANs	/48 sites	Nibble	Typical use
/3	42,535,295,865,117,307,932,921,825,928,971,026,432 (2^125)	2,305,843,009,213,693,952	35,184,372,088,832	No	All global unicast (2000::/3)
/16	5,192,296,858,534,827,628,530,496,329,220,096 (2^112)	281,474,976,710,656	4,294,967,296	Yes
/20	324,518,553,658,426,726,783,156,020,576,256 (2^108)	17,592,186,044,416	268,435,456	Yes	Large provider allocation (RIPE minimum for some)
/29	633,825,300,114,114,700,748,351,602,688 (2^99)	34,359,738,368	524,288	No	RIPE allocation to a provider (often)
/32	79,228,162,514,264,337,593,543,950,336 (2^96)	4,294,967,296	65,536	Yes	Provider allocation (RIPE default)
/36	4,951,760,157,141,521,099,596,496,896 (2^92)	268,435,456	4,096	Yes
/40	309,485,009,821,345,068,724,781,056 (2^88)	16,777,216	256	Yes
/44	19,342,813,113,834,066,795,298,816 (2^84)	1,048,576	16	Yes
/48	1,208,925,819,614,629,174,706,176 (2^80)	65,536	1	Yes	One site or organisation (RIPE PI / assignment)
/52	75,557,863,725,914,323,419,136 (2^76)	4,096		Yes
/56	4,722,366,482,869,645,213,696 (2^72)	256		Yes	Small site or home (common provider assignment)
/60	295,147,905,179,352,825,856 (2^68)	16		Yes	Some home broadband (16 LANs)
/64	18,446,744,073,709,551,616 (2^64)	1		Yes	One LAN or VLAN (needed for SLAAC)
/72	72,057,594,037,927,936 (2^56)	1/256 of a /64		Yes
/80	281,474,976,710,656 (2^48)	1/65,536 of a /64		Yes
/96	4,294,967,296	1/4,294,967,296 of a /64		Yes	Embeds an IPv4 address (NAT64)
/112	65,536	1/281,474,976,710,656 of a /64		Yes
/120	256	1/72,057,594,037,927,936 of a /64		Yes
/124	16	1/1,152,921,504,606,846,976 of a /64		Yes
/126	4	1/4,611,686,018,427,387,904 of a /64		No
/127	2	1/9,223,372,036,854,775,808 of a /64		No	Point-to-point link (RFC 6164)
/128	1	1/18,446,744,073,709,551,616 of a /64		Yes	One host or loopback

Private and special ranges

IPv4

Special-purpose ranges
Range	Name	What it is
`255.255.255.255/32`	Limited broadcast	Every host on the local network
`0.0.0.0/8`	This network	Not routed; 0.0.0.0 means "any address" in settings
`10.0.0.0/8`	Private (RFC 1918)	Office and home networks; not routed on the internet
`100.64.0.0/10`	Shared address space (CGNAT)	Used by providers behind carrier-grade NAT (RFC 6598)
`127.0.0.0/8`	Loopback	This computer
`169.254.0.0/16`	Link-local (APIPA)	Self-assigned when no DHCP server answers
`172.16.0.0/12`	Private (RFC 1918)	Office and home networks; not routed on the internet
`192.0.0.0/24`	IETF protocol assignments	Special uses such as DS-Lite
`192.0.2.0/24`	Documentation (TEST-NET-1)	For examples; never used on a network
`192.88.99.0/24`	6to4 relay (deprecated)	Formerly anycast for 6to4
`192.168.0.0/16`	Private (RFC 1918)	Office and home networks; not routed on the internet
`198.18.0.0/15`	Benchmarking	Network equipment testing (RFC 2544)
`198.51.100.0/24`	Documentation (TEST-NET-2)	For examples; never used on a network
`203.0.113.0/24`	Documentation (TEST-NET-3)	For examples; never used on a network
`224.0.0.0/4`	Multicast	One-to-many traffic, such as IPTV and routing protocols
`240.0.0.0/4`	Reserved	Future use; not usable on most systems

IPv6

Special-purpose ranges
Range	Name	What it is
`::/128`	Unspecified	No address; :: means "any address" in settings
`::1/128`	Loopback	This computer
`::ffff:0:0/96`	IPv4-mapped	An IPv4 address written as IPv6
`64:ff9b::/96`	NAT64	IPv4 addresses reached through a NAT64 gateway
`100::/64`	Discard only	Traffic sent here is dropped (RFC 6666)
`2001:db8::/32`	Documentation	For examples; never used on a network
`2001::/32`	Teredo	IPv6 tunnelled over IPv4 UDP
`2002::/16`	6to4	IPv6 tunnelled over IPv4 (largely retired)
`3fff::/20`	Documentation	For examples (RFC 9637)
`fc00::/7`	Unique local (ULA)	Private IPv6, like RFC 1918; usually fd00::/8
`fe80::/10`	Link-local	Every IPv6 interface has one; not routed
`ff00::/8`	Multicast	One-to-many traffic; replaces broadcast
`2000::/3`	Global unicast	Public 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.

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IP subnet calculator

IPv4 CIDR reference (/0 to /32)

IPv6 prefix reference

Private and special ranges

IPv4

IPv6

About this tool

Common questions

IPv4 CIDR reference (/0 to /32)

IPv6 prefix reference

Private and special ranges

IPv4

IPv6

Common questions

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