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.

Network42.0.0.0/9

Usable hosts8,388,606

Subnet mask255.128.0.0

Addresses8,388,608

Network address: 42.0.0.0
Broadcast address: 42.127.255.255
First usable: 42.0.0.1
Last usable: 42.127.255.254
Usable hosts: 8,388,606 (8,388,608 less the network and broadcast addresses)
Subnet mask: 255.128.0.0
Wildcard mask: 0.127.255.255 (Cisco ACLs, OSPF)
Prefix length: /9
Type: Public public
Old class: A (default /8)
As numbers: Hex 2A000000 · Integer 704643072 to 713031679
Reverse DNS zones: 0.42.in-addr.arpa
1.42.in-addr.arpa
2.42.in-addr.arpa
3.42.in-addr.arpa
4.42.in-addr.arpa
5.42.in-addr.arpa
6.42.in-addr.arpa
7.42.in-addr.arpa
8.42.in-addr.arpa
9.42.in-addr.arpa
10.42.in-addr.arpa
11.42.in-addr.arpa
12.42.in-addr.arpa
13.42.in-addr.arpa
14.42.in-addr.arpa
15.42.in-addr.arpa
and 112 more
/9 is not on a 8-bit boundary, so it takes 128 /16 zones.

Binary

Binary view
	Binary (network bits bold, host bits grey)	Dotted
Address	`00101010.00000000.00000000.00000000`	`42.0.0.0`
Subnet mask	`11111111.10000000.00000000.00000000`	`255.128.0.0`
Network	`00101010.00000000.00000000.00000000`	`42.0.0.0`
Broadcast	`00101010.01111111.11111111.11111111`	`42.127.255.255`

Split into smaller subnets/16

/10 (2)/11 (4)/12 (8)/13 (16)/14 (32)/15 (64)/16 (128)/17 (256)/18 (512)/19 (1,024)/20 (2,048)/21 (4,096)

42.0.0.0/9 makes 128 subnets of /16.

Subnets
#	Subnet	Usable hosts range	Broadcast	Hosts
1	`42.0.0.0/16`	`42.0.0.1` to `42.0.255.254`	42.0.255.255	65,534
2	`42.1.0.0/16`	`42.1.0.1` to `42.1.255.254`	42.1.255.255	65,534
3	`42.2.0.0/16`	`42.2.0.1` to `42.2.255.254`	42.2.255.255	65,534
4	`42.3.0.0/16`	`42.3.0.1` to `42.3.255.254`	42.3.255.255	65,534
5	`42.4.0.0/16`	`42.4.0.1` to `42.4.255.254`	42.4.255.255	65,534
6	`42.5.0.0/16`	`42.5.0.1` to `42.5.255.254`	42.5.255.255	65,534
7	`42.6.0.0/16`	`42.6.0.1` to `42.6.255.254`	42.6.255.255	65,534
8	`42.7.0.0/16`	`42.7.0.1` to `42.7.255.254`	42.7.255.255	65,534
9	`42.8.0.0/16`	`42.8.0.1` to `42.8.255.254`	42.8.255.255	65,534
10	`42.9.0.0/16`	`42.9.0.1` to `42.9.255.254`	42.9.255.255	65,534
11	`42.10.0.0/16`	`42.10.0.1` to `42.10.255.254`	42.10.255.255	65,534
12	`42.11.0.0/16`	`42.11.0.1` to `42.11.255.254`	42.11.255.255	65,534
13	`42.12.0.0/16`	`42.12.0.1` to `42.12.255.254`	42.12.255.255	65,534
14	`42.13.0.0/16`	`42.13.0.1` to `42.13.255.254`	42.13.255.255	65,534
15	`42.14.0.0/16`	`42.14.0.1` to `42.14.255.254`	42.14.255.255	65,534
16	`42.15.0.0/16`	`42.15.0.1` to `42.15.255.254`	42.15.255.255	65,534
17	`42.16.0.0/16`	`42.16.0.1` to `42.16.255.254`	42.16.255.255	65,534
18	`42.17.0.0/16`	`42.17.0.1` to `42.17.255.254`	42.17.255.255	65,534
19	`42.18.0.0/16`	`42.18.0.1` to `42.18.255.254`	42.18.255.255	65,534
20	`42.19.0.0/16`	`42.19.0.1` to `42.19.255.254`	42.19.255.255	65,534
21	`42.20.0.0/16`	`42.20.0.1` to `42.20.255.254`	42.20.255.255	65,534
22	`42.21.0.0/16`	`42.21.0.1` to `42.21.255.254`	42.21.255.255	65,534
23	`42.22.0.0/16`	`42.22.0.1` to `42.22.255.254`	42.22.255.255	65,534
24	`42.23.0.0/16`	`42.23.0.1` to `42.23.255.254`	42.23.255.255	65,534
25	`42.24.0.0/16`	`42.24.0.1` to `42.24.255.254`	42.24.255.255	65,534
26	`42.25.0.0/16`	`42.25.0.1` to `42.25.255.254`	42.25.255.255	65,534
27	`42.26.0.0/16`	`42.26.0.1` to `42.26.255.254`	42.26.255.255	65,534
28	`42.27.0.0/16`	`42.27.0.1` to `42.27.255.254`	42.27.255.255	65,534
29	`42.28.0.0/16`	`42.28.0.1` to `42.28.255.254`	42.28.255.255	65,534
30	`42.29.0.0/16`	`42.29.0.1` to `42.29.255.254`	42.29.255.255	65,534
31	`42.30.0.0/16`	`42.30.0.1` to `42.30.255.254`	42.30.255.255	65,534
32	`42.31.0.0/16`	`42.31.0.1` to `42.31.255.254`	42.31.255.255	65,534
33	`42.32.0.0/16`	`42.32.0.1` to `42.32.255.254`	42.32.255.255	65,534
34	`42.33.0.0/16`	`42.33.0.1` to `42.33.255.254`	42.33.255.255	65,534
35	`42.34.0.0/16`	`42.34.0.1` to `42.34.255.254`	42.34.255.255	65,534
36	`42.35.0.0/16`	`42.35.0.1` to `42.35.255.254`	42.35.255.255	65,534
37	`42.36.0.0/16`	`42.36.0.1` to `42.36.255.254`	42.36.255.255	65,534
38	`42.37.0.0/16`	`42.37.0.1` to `42.37.255.254`	42.37.255.255	65,534
39	`42.38.0.0/16`	`42.38.0.1` to `42.38.255.254`	42.38.255.255	65,534
40	`42.39.0.0/16`	`42.39.0.1` to `42.39.255.254`	42.39.255.255	65,534
41	`42.40.0.0/16`	`42.40.0.1` to `42.40.255.254`	42.40.255.255	65,534
42	`42.41.0.0/16`	`42.41.0.1` to `42.41.255.254`	42.41.255.255	65,534
43	`42.42.0.0/16`	`42.42.0.1` to `42.42.255.254`	42.42.255.255	65,534
44	`42.43.0.0/16`	`42.43.0.1` to `42.43.255.254`	42.43.255.255	65,534
45	`42.44.0.0/16`	`42.44.0.1` to `42.44.255.254`	42.44.255.255	65,534
46	`42.45.0.0/16`	`42.45.0.1` to `42.45.255.254`	42.45.255.255	65,534
47	`42.46.0.0/16`	`42.46.0.1` to `42.46.255.254`	42.46.255.255	65,534
48	`42.47.0.0/16`	`42.47.0.1` to `42.47.255.254`	42.47.255.255	65,534
49	`42.48.0.0/16`	`42.48.0.1` to `42.48.255.254`	42.48.255.255	65,534
50	`42.49.0.0/16`	`42.49.0.1` to `42.49.255.254`	42.49.255.255	65,534
51	`42.50.0.0/16`	`42.50.0.1` to `42.50.255.254`	42.50.255.255	65,534
52	`42.51.0.0/16`	`42.51.0.1` to `42.51.255.254`	42.51.255.255	65,534
53	`42.52.0.0/16`	`42.52.0.1` to `42.52.255.254`	42.52.255.255	65,534
54	`42.53.0.0/16`	`42.53.0.1` to `42.53.255.254`	42.53.255.255	65,534
55	`42.54.0.0/16`	`42.54.0.1` to `42.54.255.254`	42.54.255.255	65,534
56	`42.55.0.0/16`	`42.55.0.1` to `42.55.255.254`	42.55.255.255	65,534
57	`42.56.0.0/16`	`42.56.0.1` to `42.56.255.254`	42.56.255.255	65,534
58	`42.57.0.0/16`	`42.57.0.1` to `42.57.255.254`	42.57.255.255	65,534
59	`42.58.0.0/16`	`42.58.0.1` to `42.58.255.254`	42.58.255.255	65,534
60	`42.59.0.0/16`	`42.59.0.1` to `42.59.255.254`	42.59.255.255	65,534
61	`42.60.0.0/16`	`42.60.0.1` to `42.60.255.254`	42.60.255.255	65,534
62	`42.61.0.0/16`	`42.61.0.1` to `42.61.255.254`	42.61.255.255	65,534
63	`42.62.0.0/16`	`42.62.0.1` to `42.62.255.254`	42.62.255.255	65,534
64	`42.63.0.0/16`	`42.63.0.1` to `42.63.255.254`	42.63.255.255	65,534
65	`42.64.0.0/16`	`42.64.0.1` to `42.64.255.254`	42.64.255.255	65,534
66	`42.65.0.0/16`	`42.65.0.1` to `42.65.255.254`	42.65.255.255	65,534
67	`42.66.0.0/16`	`42.66.0.1` to `42.66.255.254`	42.66.255.255	65,534
68	`42.67.0.0/16`	`42.67.0.1` to `42.67.255.254`	42.67.255.255	65,534
69	`42.68.0.0/16`	`42.68.0.1` to `42.68.255.254`	42.68.255.255	65,534
70	`42.69.0.0/16`	`42.69.0.1` to `42.69.255.254`	42.69.255.255	65,534
71	`42.70.0.0/16`	`42.70.0.1` to `42.70.255.254`	42.70.255.255	65,534
72	`42.71.0.0/16`	`42.71.0.1` to `42.71.255.254`	42.71.255.255	65,534
73	`42.72.0.0/16`	`42.72.0.1` to `42.72.255.254`	42.72.255.255	65,534
74	`42.73.0.0/16`	`42.73.0.1` to `42.73.255.254`	42.73.255.255	65,534
75	`42.74.0.0/16`	`42.74.0.1` to `42.74.255.254`	42.74.255.255	65,534
76	`42.75.0.0/16`	`42.75.0.1` to `42.75.255.254`	42.75.255.255	65,534
77	`42.76.0.0/16`	`42.76.0.1` to `42.76.255.254`	42.76.255.255	65,534
78	`42.77.0.0/16`	`42.77.0.1` to `42.77.255.254`	42.77.255.255	65,534
79	`42.78.0.0/16`	`42.78.0.1` to `42.78.255.254`	42.78.255.255	65,534
80	`42.79.0.0/16`	`42.79.0.1` to `42.79.255.254`	42.79.255.255	65,534
81	`42.80.0.0/16`	`42.80.0.1` to `42.80.255.254`	42.80.255.255	65,534
82	`42.81.0.0/16`	`42.81.0.1` to `42.81.255.254`	42.81.255.255	65,534
83	`42.82.0.0/16`	`42.82.0.1` to `42.82.255.254`	42.82.255.255	65,534
84	`42.83.0.0/16`	`42.83.0.1` to `42.83.255.254`	42.83.255.255	65,534
85	`42.84.0.0/16`	`42.84.0.1` to `42.84.255.254`	42.84.255.255	65,534
86	`42.85.0.0/16`	`42.85.0.1` to `42.85.255.254`	42.85.255.255	65,534
87	`42.86.0.0/16`	`42.86.0.1` to `42.86.255.254`	42.86.255.255	65,534
88	`42.87.0.0/16`	`42.87.0.1` to `42.87.255.254`	42.87.255.255	65,534
89	`42.88.0.0/16`	`42.88.0.1` to `42.88.255.254`	42.88.255.255	65,534
90	`42.89.0.0/16`	`42.89.0.1` to `42.89.255.254`	42.89.255.255	65,534
91	`42.90.0.0/16`	`42.90.0.1` to `42.90.255.254`	42.90.255.255	65,534
92	`42.91.0.0/16`	`42.91.0.1` to `42.91.255.254`	42.91.255.255	65,534
93	`42.92.0.0/16`	`42.92.0.1` to `42.92.255.254`	42.92.255.255	65,534
94	`42.93.0.0/16`	`42.93.0.1` to `42.93.255.254`	42.93.255.255	65,534
95	`42.94.0.0/16`	`42.94.0.1` to `42.94.255.254`	42.94.255.255	65,534
96	`42.95.0.0/16`	`42.95.0.1` to `42.95.255.254`	42.95.255.255	65,534
97	`42.96.0.0/16`	`42.96.0.1` to `42.96.255.254`	42.96.255.255	65,534
98	`42.97.0.0/16`	`42.97.0.1` to `42.97.255.254`	42.97.255.255	65,534
99	`42.98.0.0/16`	`42.98.0.1` to `42.98.255.254`	42.98.255.255	65,534
100	`42.99.0.0/16`	`42.99.0.1` to `42.99.255.254`	42.99.255.255	65,534
101	`42.100.0.0/16`	`42.100.0.1` to `42.100.255.254`	42.100.255.255	65,534
102	`42.101.0.0/16`	`42.101.0.1` to `42.101.255.254`	42.101.255.255	65,534
103	`42.102.0.0/16`	`42.102.0.1` to `42.102.255.254`	42.102.255.255	65,534
104	`42.103.0.0/16`	`42.103.0.1` to `42.103.255.254`	42.103.255.255	65,534
105	`42.104.0.0/16`	`42.104.0.1` to `42.104.255.254`	42.104.255.255	65,534
106	`42.105.0.0/16`	`42.105.0.1` to `42.105.255.254`	42.105.255.255	65,534
107	`42.106.0.0/16`	`42.106.0.1` to `42.106.255.254`	42.106.255.255	65,534
108	`42.107.0.0/16`	`42.107.0.1` to `42.107.255.254`	42.107.255.255	65,534
109	`42.108.0.0/16`	`42.108.0.1` to `42.108.255.254`	42.108.255.255	65,534
110	`42.109.0.0/16`	`42.109.0.1` to `42.109.255.254`	42.109.255.255	65,534
111	`42.110.0.0/16`	`42.110.0.1` to `42.110.255.254`	42.110.255.255	65,534
112	`42.111.0.0/16`	`42.111.0.1` to `42.111.255.254`	42.111.255.255	65,534
113	`42.112.0.0/16`	`42.112.0.1` to `42.112.255.254`	42.112.255.255	65,534
114	`42.113.0.0/16`	`42.113.0.1` to `42.113.255.254`	42.113.255.255	65,534
115	`42.114.0.0/16`	`42.114.0.1` to `42.114.255.254`	42.114.255.255	65,534
116	`42.115.0.0/16`	`42.115.0.1` to `42.115.255.254`	42.115.255.255	65,534
117	`42.116.0.0/16`	`42.116.0.1` to `42.116.255.254`	42.116.255.255	65,534
118	`42.117.0.0/16`	`42.117.0.1` to `42.117.255.254`	42.117.255.255	65,534
119	`42.118.0.0/16`	`42.118.0.1` to `42.118.255.254`	42.118.255.255	65,534
120	`42.119.0.0/16`	`42.119.0.1` to `42.119.255.254`	42.119.255.255	65,534
121	`42.120.0.0/16`	`42.120.0.1` to `42.120.255.254`	42.120.255.255	65,534
122	`42.121.0.0/16`	`42.121.0.1` to `42.121.255.254`	42.121.255.255	65,534
123	`42.122.0.0/16`	`42.122.0.1` to `42.122.255.254`	42.122.255.255	65,534
124	`42.123.0.0/16`	`42.123.0.1` to `42.123.255.254`	42.123.255.255	65,534
125	`42.124.0.0/16`	`42.124.0.1` to `42.124.255.254`	42.124.255.255	65,534
126	`42.125.0.0/16`	`42.125.0.1` to `42.125.255.254`	42.125.255.255	65,534
127	`42.126.0.0/16`	`42.126.0.1` to `42.126.255.254`	42.126.255.255	65,534
128	`42.127.0.0/16`	`42.127.0.1` to `42.127.255.254`	42.127.255.255	65,534

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

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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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