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.

Network21.2.0.0/15

Usable hosts131,070

Subnet mask255.254.0.0

Addresses131,072

Network address: 21.2.0.0
Broadcast address: 21.3.255.255
First usable: 21.2.0.1
Last usable: 21.3.255.254
Usable hosts: 131,070 (131,072 less the network and broadcast addresses)
Subnet mask: 255.254.0.0
Wildcard mask: 0.1.255.255 (Cisco ACLs, OSPF)
Prefix length: /15
Type: Public public
Old class: A (default /8)
As numbers: Hex 15020000 · Integer 352452608 to 352583679
Reverse DNS zones: 2.21.in-addr.arpa
3.21.in-addr.arpa
/15 is not on a 8-bit boundary, so it takes 2 /16 zones.

Binary

Binary view
	Binary (network bits bold, host bits grey)	Dotted
Address	`00010101.00000010.00000000.00000000`	`21.2.0.0`
Subnet mask	`11111111.11111110.00000000.00000000`	`255.254.0.0`
Network	`00010101.00000010.00000000.00000000`	`21.2.0.0`
Broadcast	`00010101.00000011.11111111.11111111`	`21.3.255.255`

Split into smaller subnets/23

/16 (2)/17 (4)/18 (8)/19 (16)/20 (32)/21 (64)/22 (128)/23 (256)/24 (512)/25 (1,024)/26 (2,048)/27 (4,096)

21.2.0.0/15 makes 256 subnets of /23.

Subnets
#	Subnet	Usable hosts range	Broadcast	Hosts
1	`21.2.0.0/23`	`21.2.0.1` to `21.2.1.254`	21.2.1.255	510
2	`21.2.2.0/23`	`21.2.2.1` to `21.2.3.254`	21.2.3.255	510
3	`21.2.4.0/23`	`21.2.4.1` to `21.2.5.254`	21.2.5.255	510
4	`21.2.6.0/23`	`21.2.6.1` to `21.2.7.254`	21.2.7.255	510
5	`21.2.8.0/23`	`21.2.8.1` to `21.2.9.254`	21.2.9.255	510
6	`21.2.10.0/23`	`21.2.10.1` to `21.2.11.254`	21.2.11.255	510
7	`21.2.12.0/23`	`21.2.12.1` to `21.2.13.254`	21.2.13.255	510
8	`21.2.14.0/23`	`21.2.14.1` to `21.2.15.254`	21.2.15.255	510
9	`21.2.16.0/23`	`21.2.16.1` to `21.2.17.254`	21.2.17.255	510
10	`21.2.18.0/23`	`21.2.18.1` to `21.2.19.254`	21.2.19.255	510
11	`21.2.20.0/23`	`21.2.20.1` to `21.2.21.254`	21.2.21.255	510
12	`21.2.22.0/23`	`21.2.22.1` to `21.2.23.254`	21.2.23.255	510
13	`21.2.24.0/23`	`21.2.24.1` to `21.2.25.254`	21.2.25.255	510
14	`21.2.26.0/23`	`21.2.26.1` to `21.2.27.254`	21.2.27.255	510
15	`21.2.28.0/23`	`21.2.28.1` to `21.2.29.254`	21.2.29.255	510
16	`21.2.30.0/23`	`21.2.30.1` to `21.2.31.254`	21.2.31.255	510
17	`21.2.32.0/23`	`21.2.32.1` to `21.2.33.254`	21.2.33.255	510
18	`21.2.34.0/23`	`21.2.34.1` to `21.2.35.254`	21.2.35.255	510
19	`21.2.36.0/23`	`21.2.36.1` to `21.2.37.254`	21.2.37.255	510
20	`21.2.38.0/23`	`21.2.38.1` to `21.2.39.254`	21.2.39.255	510
21	`21.2.40.0/23`	`21.2.40.1` to `21.2.41.254`	21.2.41.255	510
22	`21.2.42.0/23`	`21.2.42.1` to `21.2.43.254`	21.2.43.255	510
23	`21.2.44.0/23`	`21.2.44.1` to `21.2.45.254`	21.2.45.255	510
24	`21.2.46.0/23`	`21.2.46.1` to `21.2.47.254`	21.2.47.255	510
25	`21.2.48.0/23`	`21.2.48.1` to `21.2.49.254`	21.2.49.255	510
26	`21.2.50.0/23`	`21.2.50.1` to `21.2.51.254`	21.2.51.255	510
27	`21.2.52.0/23`	`21.2.52.1` to `21.2.53.254`	21.2.53.255	510
28	`21.2.54.0/23`	`21.2.54.1` to `21.2.55.254`	21.2.55.255	510
29	`21.2.56.0/23`	`21.2.56.1` to `21.2.57.254`	21.2.57.255	510
30	`21.2.58.0/23`	`21.2.58.1` to `21.2.59.254`	21.2.59.255	510
31	`21.2.60.0/23`	`21.2.60.1` to `21.2.61.254`	21.2.61.255	510
32	`21.2.62.0/23`	`21.2.62.1` to `21.2.63.254`	21.2.63.255	510
33	`21.2.64.0/23`	`21.2.64.1` to `21.2.65.254`	21.2.65.255	510
34	`21.2.66.0/23`	`21.2.66.1` to `21.2.67.254`	21.2.67.255	510
35	`21.2.68.0/23`	`21.2.68.1` to `21.2.69.254`	21.2.69.255	510
36	`21.2.70.0/23`	`21.2.70.1` to `21.2.71.254`	21.2.71.255	510
37	`21.2.72.0/23`	`21.2.72.1` to `21.2.73.254`	21.2.73.255	510
38	`21.2.74.0/23`	`21.2.74.1` to `21.2.75.254`	21.2.75.255	510
39	`21.2.76.0/23`	`21.2.76.1` to `21.2.77.254`	21.2.77.255	510
40	`21.2.78.0/23`	`21.2.78.1` to `21.2.79.254`	21.2.79.255	510
41	`21.2.80.0/23`	`21.2.80.1` to `21.2.81.254`	21.2.81.255	510
42	`21.2.82.0/23`	`21.2.82.1` to `21.2.83.254`	21.2.83.255	510
43	`21.2.84.0/23`	`21.2.84.1` to `21.2.85.254`	21.2.85.255	510
44	`21.2.86.0/23`	`21.2.86.1` to `21.2.87.254`	21.2.87.255	510
45	`21.2.88.0/23`	`21.2.88.1` to `21.2.89.254`	21.2.89.255	510
46	`21.2.90.0/23`	`21.2.90.1` to `21.2.91.254`	21.2.91.255	510
47	`21.2.92.0/23`	`21.2.92.1` to `21.2.93.254`	21.2.93.255	510
48	`21.2.94.0/23`	`21.2.94.1` to `21.2.95.254`	21.2.95.255	510
49	`21.2.96.0/23`	`21.2.96.1` to `21.2.97.254`	21.2.97.255	510
50	`21.2.98.0/23`	`21.2.98.1` to `21.2.99.254`	21.2.99.255	510
51	`21.2.100.0/23`	`21.2.100.1` to `21.2.101.254`	21.2.101.255	510
52	`21.2.102.0/23`	`21.2.102.1` to `21.2.103.254`	21.2.103.255	510
53	`21.2.104.0/23`	`21.2.104.1` to `21.2.105.254`	21.2.105.255	510
54	`21.2.106.0/23`	`21.2.106.1` to `21.2.107.254`	21.2.107.255	510
55	`21.2.108.0/23`	`21.2.108.1` to `21.2.109.254`	21.2.109.255	510
56	`21.2.110.0/23`	`21.2.110.1` to `21.2.111.254`	21.2.111.255	510
57	`21.2.112.0/23`	`21.2.112.1` to `21.2.113.254`	21.2.113.255	510
58	`21.2.114.0/23`	`21.2.114.1` to `21.2.115.254`	21.2.115.255	510
59	`21.2.116.0/23`	`21.2.116.1` to `21.2.117.254`	21.2.117.255	510
60	`21.2.118.0/23`	`21.2.118.1` to `21.2.119.254`	21.2.119.255	510
61	`21.2.120.0/23`	`21.2.120.1` to `21.2.121.254`	21.2.121.255	510
62	`21.2.122.0/23`	`21.2.122.1` to `21.2.123.254`	21.2.123.255	510
63	`21.2.124.0/23`	`21.2.124.1` to `21.2.125.254`	21.2.125.255	510
64	`21.2.126.0/23`	`21.2.126.1` to `21.2.127.254`	21.2.127.255	510
65	`21.2.128.0/23`	`21.2.128.1` to `21.2.129.254`	21.2.129.255	510
66	`21.2.130.0/23`	`21.2.130.1` to `21.2.131.254`	21.2.131.255	510
67	`21.2.132.0/23`	`21.2.132.1` to `21.2.133.254`	21.2.133.255	510
68	`21.2.134.0/23`	`21.2.134.1` to `21.2.135.254`	21.2.135.255	510
69	`21.2.136.0/23`	`21.2.136.1` to `21.2.137.254`	21.2.137.255	510
70	`21.2.138.0/23`	`21.2.138.1` to `21.2.139.254`	21.2.139.255	510
71	`21.2.140.0/23`	`21.2.140.1` to `21.2.141.254`	21.2.141.255	510
72	`21.2.142.0/23`	`21.2.142.1` to `21.2.143.254`	21.2.143.255	510
73	`21.2.144.0/23`	`21.2.144.1` to `21.2.145.254`	21.2.145.255	510
74	`21.2.146.0/23`	`21.2.146.1` to `21.2.147.254`	21.2.147.255	510
75	`21.2.148.0/23`	`21.2.148.1` to `21.2.149.254`	21.2.149.255	510
76	`21.2.150.0/23`	`21.2.150.1` to `21.2.151.254`	21.2.151.255	510
77	`21.2.152.0/23`	`21.2.152.1` to `21.2.153.254`	21.2.153.255	510
78	`21.2.154.0/23`	`21.2.154.1` to `21.2.155.254`	21.2.155.255	510
79	`21.2.156.0/23`	`21.2.156.1` to `21.2.157.254`	21.2.157.255	510
80	`21.2.158.0/23`	`21.2.158.1` to `21.2.159.254`	21.2.159.255	510
81	`21.2.160.0/23`	`21.2.160.1` to `21.2.161.254`	21.2.161.255	510
82	`21.2.162.0/23`	`21.2.162.1` to `21.2.163.254`	21.2.163.255	510
83	`21.2.164.0/23`	`21.2.164.1` to `21.2.165.254`	21.2.165.255	510
84	`21.2.166.0/23`	`21.2.166.1` to `21.2.167.254`	21.2.167.255	510
85	`21.2.168.0/23`	`21.2.168.1` to `21.2.169.254`	21.2.169.255	510
86	`21.2.170.0/23`	`21.2.170.1` to `21.2.171.254`	21.2.171.255	510
87	`21.2.172.0/23`	`21.2.172.1` to `21.2.173.254`	21.2.173.255	510
88	`21.2.174.0/23`	`21.2.174.1` to `21.2.175.254`	21.2.175.255	510
89	`21.2.176.0/23`	`21.2.176.1` to `21.2.177.254`	21.2.177.255	510
90	`21.2.178.0/23`	`21.2.178.1` to `21.2.179.254`	21.2.179.255	510
91	`21.2.180.0/23`	`21.2.180.1` to `21.2.181.254`	21.2.181.255	510
92	`21.2.182.0/23`	`21.2.182.1` to `21.2.183.254`	21.2.183.255	510
93	`21.2.184.0/23`	`21.2.184.1` to `21.2.185.254`	21.2.185.255	510
94	`21.2.186.0/23`	`21.2.186.1` to `21.2.187.254`	21.2.187.255	510
95	`21.2.188.0/23`	`21.2.188.1` to `21.2.189.254`	21.2.189.255	510
96	`21.2.190.0/23`	`21.2.190.1` to `21.2.191.254`	21.2.191.255	510
97	`21.2.192.0/23`	`21.2.192.1` to `21.2.193.254`	21.2.193.255	510
98	`21.2.194.0/23`	`21.2.194.1` to `21.2.195.254`	21.2.195.255	510
99	`21.2.196.0/23`	`21.2.196.1` to `21.2.197.254`	21.2.197.255	510
100	`21.2.198.0/23`	`21.2.198.1` to `21.2.199.254`	21.2.199.255	510
101	`21.2.200.0/23`	`21.2.200.1` to `21.2.201.254`	21.2.201.255	510
102	`21.2.202.0/23`	`21.2.202.1` to `21.2.203.254`	21.2.203.255	510
103	`21.2.204.0/23`	`21.2.204.1` to `21.2.205.254`	21.2.205.255	510
104	`21.2.206.0/23`	`21.2.206.1` to `21.2.207.254`	21.2.207.255	510
105	`21.2.208.0/23`	`21.2.208.1` to `21.2.209.254`	21.2.209.255	510
106	`21.2.210.0/23`	`21.2.210.1` to `21.2.211.254`	21.2.211.255	510
107	`21.2.212.0/23`	`21.2.212.1` to `21.2.213.254`	21.2.213.255	510
108	`21.2.214.0/23`	`21.2.214.1` to `21.2.215.254`	21.2.215.255	510
109	`21.2.216.0/23`	`21.2.216.1` to `21.2.217.254`	21.2.217.255	510
110	`21.2.218.0/23`	`21.2.218.1` to `21.2.219.254`	21.2.219.255	510
111	`21.2.220.0/23`	`21.2.220.1` to `21.2.221.254`	21.2.221.255	510
112	`21.2.222.0/23`	`21.2.222.1` to `21.2.223.254`	21.2.223.255	510
113	`21.2.224.0/23`	`21.2.224.1` to `21.2.225.254`	21.2.225.255	510
114	`21.2.226.0/23`	`21.2.226.1` to `21.2.227.254`	21.2.227.255	510
115	`21.2.228.0/23`	`21.2.228.1` to `21.2.229.254`	21.2.229.255	510
116	`21.2.230.0/23`	`21.2.230.1` to `21.2.231.254`	21.2.231.255	510
117	`21.2.232.0/23`	`21.2.232.1` to `21.2.233.254`	21.2.233.255	510
118	`21.2.234.0/23`	`21.2.234.1` to `21.2.235.254`	21.2.235.255	510
119	`21.2.236.0/23`	`21.2.236.1` to `21.2.237.254`	21.2.237.255	510
120	`21.2.238.0/23`	`21.2.238.1` to `21.2.239.254`	21.2.239.255	510
121	`21.2.240.0/23`	`21.2.240.1` to `21.2.241.254`	21.2.241.255	510
122	`21.2.242.0/23`	`21.2.242.1` to `21.2.243.254`	21.2.243.255	510
123	`21.2.244.0/23`	`21.2.244.1` to `21.2.245.254`	21.2.245.255	510
124	`21.2.246.0/23`	`21.2.246.1` to `21.2.247.254`	21.2.247.255	510
125	`21.2.248.0/23`	`21.2.248.1` to `21.2.249.254`	21.2.249.255	510
126	`21.2.250.0/23`	`21.2.250.1` to `21.2.251.254`	21.2.251.255	510
127	`21.2.252.0/23`	`21.2.252.1` to `21.2.253.254`	21.2.253.255	510
128	`21.2.254.0/23`	`21.2.254.1` to `21.2.255.254`	21.2.255.255	510
129	`21.3.0.0/23`	`21.3.0.1` to `21.3.1.254`	21.3.1.255	510
130	`21.3.2.0/23`	`21.3.2.1` to `21.3.3.254`	21.3.3.255	510
131	`21.3.4.0/23`	`21.3.4.1` to `21.3.5.254`	21.3.5.255	510
132	`21.3.6.0/23`	`21.3.6.1` to `21.3.7.254`	21.3.7.255	510
133	`21.3.8.0/23`	`21.3.8.1` to `21.3.9.254`	21.3.9.255	510
134	`21.3.10.0/23`	`21.3.10.1` to `21.3.11.254`	21.3.11.255	510
135	`21.3.12.0/23`	`21.3.12.1` to `21.3.13.254`	21.3.13.255	510
136	`21.3.14.0/23`	`21.3.14.1` to `21.3.15.254`	21.3.15.255	510
137	`21.3.16.0/23`	`21.3.16.1` to `21.3.17.254`	21.3.17.255	510
138	`21.3.18.0/23`	`21.3.18.1` to `21.3.19.254`	21.3.19.255	510
139	`21.3.20.0/23`	`21.3.20.1` to `21.3.21.254`	21.3.21.255	510
140	`21.3.22.0/23`	`21.3.22.1` to `21.3.23.254`	21.3.23.255	510
141	`21.3.24.0/23`	`21.3.24.1` to `21.3.25.254`	21.3.25.255	510
142	`21.3.26.0/23`	`21.3.26.1` to `21.3.27.254`	21.3.27.255	510
143	`21.3.28.0/23`	`21.3.28.1` to `21.3.29.254`	21.3.29.255	510
144	`21.3.30.0/23`	`21.3.30.1` to `21.3.31.254`	21.3.31.255	510
145	`21.3.32.0/23`	`21.3.32.1` to `21.3.33.254`	21.3.33.255	510
146	`21.3.34.0/23`	`21.3.34.1` to `21.3.35.254`	21.3.35.255	510
147	`21.3.36.0/23`	`21.3.36.1` to `21.3.37.254`	21.3.37.255	510
148	`21.3.38.0/23`	`21.3.38.1` to `21.3.39.254`	21.3.39.255	510
149	`21.3.40.0/23`	`21.3.40.1` to `21.3.41.254`	21.3.41.255	510
150	`21.3.42.0/23`	`21.3.42.1` to `21.3.43.254`	21.3.43.255	510
151	`21.3.44.0/23`	`21.3.44.1` to `21.3.45.254`	21.3.45.255	510
152	`21.3.46.0/23`	`21.3.46.1` to `21.3.47.254`	21.3.47.255	510
153	`21.3.48.0/23`	`21.3.48.1` to `21.3.49.254`	21.3.49.255	510
154	`21.3.50.0/23`	`21.3.50.1` to `21.3.51.254`	21.3.51.255	510
155	`21.3.52.0/23`	`21.3.52.1` to `21.3.53.254`	21.3.53.255	510
156	`21.3.54.0/23`	`21.3.54.1` to `21.3.55.254`	21.3.55.255	510
157	`21.3.56.0/23`	`21.3.56.1` to `21.3.57.254`	21.3.57.255	510
158	`21.3.58.0/23`	`21.3.58.1` to `21.3.59.254`	21.3.59.255	510
159	`21.3.60.0/23`	`21.3.60.1` to `21.3.61.254`	21.3.61.255	510
160	`21.3.62.0/23`	`21.3.62.1` to `21.3.63.254`	21.3.63.255	510
161	`21.3.64.0/23`	`21.3.64.1` to `21.3.65.254`	21.3.65.255	510
162	`21.3.66.0/23`	`21.3.66.1` to `21.3.67.254`	21.3.67.255	510
163	`21.3.68.0/23`	`21.3.68.1` to `21.3.69.254`	21.3.69.255	510
164	`21.3.70.0/23`	`21.3.70.1` to `21.3.71.254`	21.3.71.255	510
165	`21.3.72.0/23`	`21.3.72.1` to `21.3.73.254`	21.3.73.255	510
166	`21.3.74.0/23`	`21.3.74.1` to `21.3.75.254`	21.3.75.255	510
167	`21.3.76.0/23`	`21.3.76.1` to `21.3.77.254`	21.3.77.255	510
168	`21.3.78.0/23`	`21.3.78.1` to `21.3.79.254`	21.3.79.255	510
169	`21.3.80.0/23`	`21.3.80.1` to `21.3.81.254`	21.3.81.255	510
170	`21.3.82.0/23`	`21.3.82.1` to `21.3.83.254`	21.3.83.255	510
171	`21.3.84.0/23`	`21.3.84.1` to `21.3.85.254`	21.3.85.255	510
172	`21.3.86.0/23`	`21.3.86.1` to `21.3.87.254`	21.3.87.255	510
173	`21.3.88.0/23`	`21.3.88.1` to `21.3.89.254`	21.3.89.255	510
174	`21.3.90.0/23`	`21.3.90.1` to `21.3.91.254`	21.3.91.255	510
175	`21.3.92.0/23`	`21.3.92.1` to `21.3.93.254`	21.3.93.255	510
176	`21.3.94.0/23`	`21.3.94.1` to `21.3.95.254`	21.3.95.255	510
177	`21.3.96.0/23`	`21.3.96.1` to `21.3.97.254`	21.3.97.255	510
178	`21.3.98.0/23`	`21.3.98.1` to `21.3.99.254`	21.3.99.255	510
179	`21.3.100.0/23`	`21.3.100.1` to `21.3.101.254`	21.3.101.255	510
180	`21.3.102.0/23`	`21.3.102.1` to `21.3.103.254`	21.3.103.255	510
181	`21.3.104.0/23`	`21.3.104.1` to `21.3.105.254`	21.3.105.255	510
182	`21.3.106.0/23`	`21.3.106.1` to `21.3.107.254`	21.3.107.255	510
183	`21.3.108.0/23`	`21.3.108.1` to `21.3.109.254`	21.3.109.255	510
184	`21.3.110.0/23`	`21.3.110.1` to `21.3.111.254`	21.3.111.255	510
185	`21.3.112.0/23`	`21.3.112.1` to `21.3.113.254`	21.3.113.255	510
186	`21.3.114.0/23`	`21.3.114.1` to `21.3.115.254`	21.3.115.255	510
187	`21.3.116.0/23`	`21.3.116.1` to `21.3.117.254`	21.3.117.255	510
188	`21.3.118.0/23`	`21.3.118.1` to `21.3.119.254`	21.3.119.255	510
189	`21.3.120.0/23`	`21.3.120.1` to `21.3.121.254`	21.3.121.255	510
190	`21.3.122.0/23`	`21.3.122.1` to `21.3.123.254`	21.3.123.255	510
191	`21.3.124.0/23`	`21.3.124.1` to `21.3.125.254`	21.3.125.255	510
192	`21.3.126.0/23`	`21.3.126.1` to `21.3.127.254`	21.3.127.255	510
193	`21.3.128.0/23`	`21.3.128.1` to `21.3.129.254`	21.3.129.255	510
194	`21.3.130.0/23`	`21.3.130.1` to `21.3.131.254`	21.3.131.255	510
195	`21.3.132.0/23`	`21.3.132.1` to `21.3.133.254`	21.3.133.255	510
196	`21.3.134.0/23`	`21.3.134.1` to `21.3.135.254`	21.3.135.255	510
197	`21.3.136.0/23`	`21.3.136.1` to `21.3.137.254`	21.3.137.255	510
198	`21.3.138.0/23`	`21.3.138.1` to `21.3.139.254`	21.3.139.255	510
199	`21.3.140.0/23`	`21.3.140.1` to `21.3.141.254`	21.3.141.255	510
200	`21.3.142.0/23`	`21.3.142.1` to `21.3.143.254`	21.3.143.255	510
201	`21.3.144.0/23`	`21.3.144.1` to `21.3.145.254`	21.3.145.255	510
202	`21.3.146.0/23`	`21.3.146.1` to `21.3.147.254`	21.3.147.255	510
203	`21.3.148.0/23`	`21.3.148.1` to `21.3.149.254`	21.3.149.255	510
204	`21.3.150.0/23`	`21.3.150.1` to `21.3.151.254`	21.3.151.255	510
205	`21.3.152.0/23`	`21.3.152.1` to `21.3.153.254`	21.3.153.255	510
206	`21.3.154.0/23`	`21.3.154.1` to `21.3.155.254`	21.3.155.255	510
207	`21.3.156.0/23`	`21.3.156.1` to `21.3.157.254`	21.3.157.255	510
208	`21.3.158.0/23`	`21.3.158.1` to `21.3.159.254`	21.3.159.255	510
209	`21.3.160.0/23`	`21.3.160.1` to `21.3.161.254`	21.3.161.255	510
210	`21.3.162.0/23`	`21.3.162.1` to `21.3.163.254`	21.3.163.255	510
211	`21.3.164.0/23`	`21.3.164.1` to `21.3.165.254`	21.3.165.255	510
212	`21.3.166.0/23`	`21.3.166.1` to `21.3.167.254`	21.3.167.255	510
213	`21.3.168.0/23`	`21.3.168.1` to `21.3.169.254`	21.3.169.255	510
214	`21.3.170.0/23`	`21.3.170.1` to `21.3.171.254`	21.3.171.255	510
215	`21.3.172.0/23`	`21.3.172.1` to `21.3.173.254`	21.3.173.255	510
216	`21.3.174.0/23`	`21.3.174.1` to `21.3.175.254`	21.3.175.255	510
217	`21.3.176.0/23`	`21.3.176.1` to `21.3.177.254`	21.3.177.255	510
218	`21.3.178.0/23`	`21.3.178.1` to `21.3.179.254`	21.3.179.255	510
219	`21.3.180.0/23`	`21.3.180.1` to `21.3.181.254`	21.3.181.255	510
220	`21.3.182.0/23`	`21.3.182.1` to `21.3.183.254`	21.3.183.255	510
221	`21.3.184.0/23`	`21.3.184.1` to `21.3.185.254`	21.3.185.255	510
222	`21.3.186.0/23`	`21.3.186.1` to `21.3.187.254`	21.3.187.255	510
223	`21.3.188.0/23`	`21.3.188.1` to `21.3.189.254`	21.3.189.255	510
224	`21.3.190.0/23`	`21.3.190.1` to `21.3.191.254`	21.3.191.255	510
225	`21.3.192.0/23`	`21.3.192.1` to `21.3.193.254`	21.3.193.255	510
226	`21.3.194.0/23`	`21.3.194.1` to `21.3.195.254`	21.3.195.255	510
227	`21.3.196.0/23`	`21.3.196.1` to `21.3.197.254`	21.3.197.255	510
228	`21.3.198.0/23`	`21.3.198.1` to `21.3.199.254`	21.3.199.255	510
229	`21.3.200.0/23`	`21.3.200.1` to `21.3.201.254`	21.3.201.255	510
230	`21.3.202.0/23`	`21.3.202.1` to `21.3.203.254`	21.3.203.255	510
231	`21.3.204.0/23`	`21.3.204.1` to `21.3.205.254`	21.3.205.255	510
232	`21.3.206.0/23`	`21.3.206.1` to `21.3.207.254`	21.3.207.255	510
233	`21.3.208.0/23`	`21.3.208.1` to `21.3.209.254`	21.3.209.255	510
234	`21.3.210.0/23`	`21.3.210.1` to `21.3.211.254`	21.3.211.255	510
235	`21.3.212.0/23`	`21.3.212.1` to `21.3.213.254`	21.3.213.255	510
236	`21.3.214.0/23`	`21.3.214.1` to `21.3.215.254`	21.3.215.255	510
237	`21.3.216.0/23`	`21.3.216.1` to `21.3.217.254`	21.3.217.255	510
238	`21.3.218.0/23`	`21.3.218.1` to `21.3.219.254`	21.3.219.255	510
239	`21.3.220.0/23`	`21.3.220.1` to `21.3.221.254`	21.3.221.255	510
240	`21.3.222.0/23`	`21.3.222.1` to `21.3.223.254`	21.3.223.255	510
241	`21.3.224.0/23`	`21.3.224.1` to `21.3.225.254`	21.3.225.255	510
242	`21.3.226.0/23`	`21.3.226.1` to `21.3.227.254`	21.3.227.255	510
243	`21.3.228.0/23`	`21.3.228.1` to `21.3.229.254`	21.3.229.255	510
244	`21.3.230.0/23`	`21.3.230.1` to `21.3.231.254`	21.3.231.255	510
245	`21.3.232.0/23`	`21.3.232.1` to `21.3.233.254`	21.3.233.255	510
246	`21.3.234.0/23`	`21.3.234.1` to `21.3.235.254`	21.3.235.255	510
247	`21.3.236.0/23`	`21.3.236.1` to `21.3.237.254`	21.3.237.255	510
248	`21.3.238.0/23`	`21.3.238.1` to `21.3.239.254`	21.3.239.255	510
249	`21.3.240.0/23`	`21.3.240.1` to `21.3.241.254`	21.3.241.255	510
250	`21.3.242.0/23`	`21.3.242.1` to `21.3.243.254`	21.3.243.255	510
251	`21.3.244.0/23`	`21.3.244.1` to `21.3.245.254`	21.3.245.255	510
252	`21.3.246.0/23`	`21.3.246.1` to `21.3.247.254`	21.3.247.255	510
253	`21.3.248.0/23`	`21.3.248.1` to `21.3.249.254`	21.3.249.255	510
254	`21.3.250.0/23`	`21.3.250.1` to `21.3.251.254`	21.3.251.255	510
255	`21.3.252.0/23`	`21.3.252.1` to `21.3.253.254`	21.3.253.255	510
256	`21.3.254.0/23`	`21.3.254.1` to `21.3.255.254`	21.3.255.255	510

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.

Internet and network

Computers and devices

Make and print

Surftec support

Surftec

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

Related tools