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.

Network100.0.0.0/7

Usable hosts33,554,430

Subnet mask254.0.0.0

Addresses33,554,432

Network address: 100.0.0.0
Broadcast address: 101.255.255.255
First usable: 100.0.0.1
Last usable: 101.255.255.254
Usable hosts: 33,554,430 (33,554,432 less the network and broadcast addresses)
Subnet mask: 254.0.0.0
Wildcard mask: 1.255.255.255 (Cisco ACLs, OSPF)
Prefix length: /7
Type: Public public
Old class: A (default /8)
As numbers: Hex 64000000 · Integer 1677721600 to 1711276031
Reverse DNS zones: 100.in-addr.arpa
101.in-addr.arpa
/7 is not on a 8-bit boundary, so it takes 2 /8 zones.

Binary

Binary view
	Binary (network bits bold, host bits grey)	Dotted
Address	`01100100.00000000.00000000.00000000`	`100.0.0.0`
Subnet mask	`11111110.00000000.00000000.00000000`	`254.0.0.0`
Network	`01100100.00000000.00000000.00000000`	`100.0.0.0`
Broadcast	`01100101.11111111.11111111.11111111`	`101.255.255.255`

Split into smaller subnets/14

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

100.0.0.0/7 makes 128 subnets of /14.

Subnets
#	Subnet	Usable hosts range	Broadcast	Hosts
1	`100.0.0.0/14`	`100.0.0.1` to `100.3.255.254`	100.3.255.255	262,142
2	`100.4.0.0/14`	`100.4.0.1` to `100.7.255.254`	100.7.255.255	262,142
3	`100.8.0.0/14`	`100.8.0.1` to `100.11.255.254`	100.11.255.255	262,142
4	`100.12.0.0/14`	`100.12.0.1` to `100.15.255.254`	100.15.255.255	262,142
5	`100.16.0.0/14`	`100.16.0.1` to `100.19.255.254`	100.19.255.255	262,142
6	`100.20.0.0/14`	`100.20.0.1` to `100.23.255.254`	100.23.255.255	262,142
7	`100.24.0.0/14`	`100.24.0.1` to `100.27.255.254`	100.27.255.255	262,142
8	`100.28.0.0/14`	`100.28.0.1` to `100.31.255.254`	100.31.255.255	262,142
9	`100.32.0.0/14`	`100.32.0.1` to `100.35.255.254`	100.35.255.255	262,142
10	`100.36.0.0/14`	`100.36.0.1` to `100.39.255.254`	100.39.255.255	262,142
11	`100.40.0.0/14`	`100.40.0.1` to `100.43.255.254`	100.43.255.255	262,142
12	`100.44.0.0/14`	`100.44.0.1` to `100.47.255.254`	100.47.255.255	262,142
13	`100.48.0.0/14`	`100.48.0.1` to `100.51.255.254`	100.51.255.255	262,142
14	`100.52.0.0/14`	`100.52.0.1` to `100.55.255.254`	100.55.255.255	262,142
15	`100.56.0.0/14`	`100.56.0.1` to `100.59.255.254`	100.59.255.255	262,142
16	`100.60.0.0/14`	`100.60.0.1` to `100.63.255.254`	100.63.255.255	262,142
17	`100.64.0.0/14`	`100.64.0.1` to `100.67.255.254`	100.67.255.255	262,142
18	`100.68.0.0/14`	`100.68.0.1` to `100.71.255.254`	100.71.255.255	262,142
19	`100.72.0.0/14`	`100.72.0.1` to `100.75.255.254`	100.75.255.255	262,142
20	`100.76.0.0/14`	`100.76.0.1` to `100.79.255.254`	100.79.255.255	262,142
21	`100.80.0.0/14`	`100.80.0.1` to `100.83.255.254`	100.83.255.255	262,142
22	`100.84.0.0/14`	`100.84.0.1` to `100.87.255.254`	100.87.255.255	262,142
23	`100.88.0.0/14`	`100.88.0.1` to `100.91.255.254`	100.91.255.255	262,142
24	`100.92.0.0/14`	`100.92.0.1` to `100.95.255.254`	100.95.255.255	262,142
25	`100.96.0.0/14`	`100.96.0.1` to `100.99.255.254`	100.99.255.255	262,142
26	`100.100.0.0/14`	`100.100.0.1` to `100.103.255.254`	100.103.255.255	262,142
27	`100.104.0.0/14`	`100.104.0.1` to `100.107.255.254`	100.107.255.255	262,142
28	`100.108.0.0/14`	`100.108.0.1` to `100.111.255.254`	100.111.255.255	262,142
29	`100.112.0.0/14`	`100.112.0.1` to `100.115.255.254`	100.115.255.255	262,142
30	`100.116.0.0/14`	`100.116.0.1` to `100.119.255.254`	100.119.255.255	262,142
31	`100.120.0.0/14`	`100.120.0.1` to `100.123.255.254`	100.123.255.255	262,142
32	`100.124.0.0/14`	`100.124.0.1` to `100.127.255.254`	100.127.255.255	262,142
33	`100.128.0.0/14`	`100.128.0.1` to `100.131.255.254`	100.131.255.255	262,142
34	`100.132.0.0/14`	`100.132.0.1` to `100.135.255.254`	100.135.255.255	262,142
35	`100.136.0.0/14`	`100.136.0.1` to `100.139.255.254`	100.139.255.255	262,142
36	`100.140.0.0/14`	`100.140.0.1` to `100.143.255.254`	100.143.255.255	262,142
37	`100.144.0.0/14`	`100.144.0.1` to `100.147.255.254`	100.147.255.255	262,142
38	`100.148.0.0/14`	`100.148.0.1` to `100.151.255.254`	100.151.255.255	262,142
39	`100.152.0.0/14`	`100.152.0.1` to `100.155.255.254`	100.155.255.255	262,142
40	`100.156.0.0/14`	`100.156.0.1` to `100.159.255.254`	100.159.255.255	262,142
41	`100.160.0.0/14`	`100.160.0.1` to `100.163.255.254`	100.163.255.255	262,142
42	`100.164.0.0/14`	`100.164.0.1` to `100.167.255.254`	100.167.255.255	262,142
43	`100.168.0.0/14`	`100.168.0.1` to `100.171.255.254`	100.171.255.255	262,142
44	`100.172.0.0/14`	`100.172.0.1` to `100.175.255.254`	100.175.255.255	262,142
45	`100.176.0.0/14`	`100.176.0.1` to `100.179.255.254`	100.179.255.255	262,142
46	`100.180.0.0/14`	`100.180.0.1` to `100.183.255.254`	100.183.255.255	262,142
47	`100.184.0.0/14`	`100.184.0.1` to `100.187.255.254`	100.187.255.255	262,142
48	`100.188.0.0/14`	`100.188.0.1` to `100.191.255.254`	100.191.255.255	262,142
49	`100.192.0.0/14`	`100.192.0.1` to `100.195.255.254`	100.195.255.255	262,142
50	`100.196.0.0/14`	`100.196.0.1` to `100.199.255.254`	100.199.255.255	262,142
51	`100.200.0.0/14`	`100.200.0.1` to `100.203.255.254`	100.203.255.255	262,142
52	`100.204.0.0/14`	`100.204.0.1` to `100.207.255.254`	100.207.255.255	262,142
53	`100.208.0.0/14`	`100.208.0.1` to `100.211.255.254`	100.211.255.255	262,142
54	`100.212.0.0/14`	`100.212.0.1` to `100.215.255.254`	100.215.255.255	262,142
55	`100.216.0.0/14`	`100.216.0.1` to `100.219.255.254`	100.219.255.255	262,142
56	`100.220.0.0/14`	`100.220.0.1` to `100.223.255.254`	100.223.255.255	262,142
57	`100.224.0.0/14`	`100.224.0.1` to `100.227.255.254`	100.227.255.255	262,142
58	`100.228.0.0/14`	`100.228.0.1` to `100.231.255.254`	100.231.255.255	262,142
59	`100.232.0.0/14`	`100.232.0.1` to `100.235.255.254`	100.235.255.255	262,142
60	`100.236.0.0/14`	`100.236.0.1` to `100.239.255.254`	100.239.255.255	262,142
61	`100.240.0.0/14`	`100.240.0.1` to `100.243.255.254`	100.243.255.255	262,142
62	`100.244.0.0/14`	`100.244.0.1` to `100.247.255.254`	100.247.255.255	262,142
63	`100.248.0.0/14`	`100.248.0.1` to `100.251.255.254`	100.251.255.255	262,142
64	`100.252.0.0/14`	`100.252.0.1` to `100.255.255.254`	100.255.255.255	262,142
65	`101.0.0.0/14`	`101.0.0.1` to `101.3.255.254`	101.3.255.255	262,142
66	`101.4.0.0/14`	`101.4.0.1` to `101.7.255.254`	101.7.255.255	262,142
67	`101.8.0.0/14`	`101.8.0.1` to `101.11.255.254`	101.11.255.255	262,142
68	`101.12.0.0/14`	`101.12.0.1` to `101.15.255.254`	101.15.255.255	262,142
69	`101.16.0.0/14`	`101.16.0.1` to `101.19.255.254`	101.19.255.255	262,142
70	`101.20.0.0/14`	`101.20.0.1` to `101.23.255.254`	101.23.255.255	262,142
71	`101.24.0.0/14`	`101.24.0.1` to `101.27.255.254`	101.27.255.255	262,142
72	`101.28.0.0/14`	`101.28.0.1` to `101.31.255.254`	101.31.255.255	262,142
73	`101.32.0.0/14`	`101.32.0.1` to `101.35.255.254`	101.35.255.255	262,142
74	`101.36.0.0/14`	`101.36.0.1` to `101.39.255.254`	101.39.255.255	262,142
75	`101.40.0.0/14`	`101.40.0.1` to `101.43.255.254`	101.43.255.255	262,142
76	`101.44.0.0/14`	`101.44.0.1` to `101.47.255.254`	101.47.255.255	262,142
77	`101.48.0.0/14`	`101.48.0.1` to `101.51.255.254`	101.51.255.255	262,142
78	`101.52.0.0/14`	`101.52.0.1` to `101.55.255.254`	101.55.255.255	262,142
79	`101.56.0.0/14`	`101.56.0.1` to `101.59.255.254`	101.59.255.255	262,142
80	`101.60.0.0/14`	`101.60.0.1` to `101.63.255.254`	101.63.255.255	262,142
81	`101.64.0.0/14`	`101.64.0.1` to `101.67.255.254`	101.67.255.255	262,142
82	`101.68.0.0/14`	`101.68.0.1` to `101.71.255.254`	101.71.255.255	262,142
83	`101.72.0.0/14`	`101.72.0.1` to `101.75.255.254`	101.75.255.255	262,142
84	`101.76.0.0/14`	`101.76.0.1` to `101.79.255.254`	101.79.255.255	262,142
85	`101.80.0.0/14`	`101.80.0.1` to `101.83.255.254`	101.83.255.255	262,142
86	`101.84.0.0/14`	`101.84.0.1` to `101.87.255.254`	101.87.255.255	262,142
87	`101.88.0.0/14`	`101.88.0.1` to `101.91.255.254`	101.91.255.255	262,142
88	`101.92.0.0/14`	`101.92.0.1` to `101.95.255.254`	101.95.255.255	262,142
89	`101.96.0.0/14`	`101.96.0.1` to `101.99.255.254`	101.99.255.255	262,142
90	`101.100.0.0/14`	`101.100.0.1` to `101.103.255.254`	101.103.255.255	262,142
91	`101.104.0.0/14`	`101.104.0.1` to `101.107.255.254`	101.107.255.255	262,142
92	`101.108.0.0/14`	`101.108.0.1` to `101.111.255.254`	101.111.255.255	262,142
93	`101.112.0.0/14`	`101.112.0.1` to `101.115.255.254`	101.115.255.255	262,142
94	`101.116.0.0/14`	`101.116.0.1` to `101.119.255.254`	101.119.255.255	262,142
95	`101.120.0.0/14`	`101.120.0.1` to `101.123.255.254`	101.123.255.255	262,142
96	`101.124.0.0/14`	`101.124.0.1` to `101.127.255.254`	101.127.255.255	262,142
97	`101.128.0.0/14`	`101.128.0.1` to `101.131.255.254`	101.131.255.255	262,142
98	`101.132.0.0/14`	`101.132.0.1` to `101.135.255.254`	101.135.255.255	262,142
99	`101.136.0.0/14`	`101.136.0.1` to `101.139.255.254`	101.139.255.255	262,142
100	`101.140.0.0/14`	`101.140.0.1` to `101.143.255.254`	101.143.255.255	262,142
101	`101.144.0.0/14`	`101.144.0.1` to `101.147.255.254`	101.147.255.255	262,142
102	`101.148.0.0/14`	`101.148.0.1` to `101.151.255.254`	101.151.255.255	262,142
103	`101.152.0.0/14`	`101.152.0.1` to `101.155.255.254`	101.155.255.255	262,142
104	`101.156.0.0/14`	`101.156.0.1` to `101.159.255.254`	101.159.255.255	262,142
105	`101.160.0.0/14`	`101.160.0.1` to `101.163.255.254`	101.163.255.255	262,142
106	`101.164.0.0/14`	`101.164.0.1` to `101.167.255.254`	101.167.255.255	262,142
107	`101.168.0.0/14`	`101.168.0.1` to `101.171.255.254`	101.171.255.255	262,142
108	`101.172.0.0/14`	`101.172.0.1` to `101.175.255.254`	101.175.255.255	262,142
109	`101.176.0.0/14`	`101.176.0.1` to `101.179.255.254`	101.179.255.255	262,142
110	`101.180.0.0/14`	`101.180.0.1` to `101.183.255.254`	101.183.255.255	262,142
111	`101.184.0.0/14`	`101.184.0.1` to `101.187.255.254`	101.187.255.255	262,142
112	`101.188.0.0/14`	`101.188.0.1` to `101.191.255.254`	101.191.255.255	262,142
113	`101.192.0.0/14`	`101.192.0.1` to `101.195.255.254`	101.195.255.255	262,142
114	`101.196.0.0/14`	`101.196.0.1` to `101.199.255.254`	101.199.255.255	262,142
115	`101.200.0.0/14`	`101.200.0.1` to `101.203.255.254`	101.203.255.255	262,142
116	`101.204.0.0/14`	`101.204.0.1` to `101.207.255.254`	101.207.255.255	262,142
117	`101.208.0.0/14`	`101.208.0.1` to `101.211.255.254`	101.211.255.255	262,142
118	`101.212.0.0/14`	`101.212.0.1` to `101.215.255.254`	101.215.255.255	262,142
119	`101.216.0.0/14`	`101.216.0.1` to `101.219.255.254`	101.219.255.255	262,142
120	`101.220.0.0/14`	`101.220.0.1` to `101.223.255.254`	101.223.255.255	262,142
121	`101.224.0.0/14`	`101.224.0.1` to `101.227.255.254`	101.227.255.255	262,142
122	`101.228.0.0/14`	`101.228.0.1` to `101.231.255.254`	101.231.255.255	262,142
123	`101.232.0.0/14`	`101.232.0.1` to `101.235.255.254`	101.235.255.255	262,142
124	`101.236.0.0/14`	`101.236.0.1` to `101.239.255.254`	101.239.255.255	262,142
125	`101.240.0.0/14`	`101.240.0.1` to `101.243.255.254`	101.243.255.255	262,142
126	`101.244.0.0/14`	`101.244.0.1` to `101.247.255.254`	101.247.255.255	262,142
127	`101.248.0.0/14`	`101.248.0.1` to `101.251.255.254`	101.251.255.255	262,142
128	`101.252.0.0/14`	`101.252.0.1` to `101.255.255.254`	101.255.255.255	262,142

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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