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.

Network100.80.0.0/12

Usable hosts1,048,574

Subnet mask255.240.0.0

Addresses1,048,576

Network address: 100.80.0.0
Broadcast address: 100.95.255.255
First usable: 100.80.0.1
Last usable: 100.95.255.254
Usable hosts: 1,048,574 (1,048,576 less the network and broadcast addresses)
Subnet mask: 255.240.0.0
Wildcard mask: 0.15.255.255 (Cisco ACLs, OSPF)
Prefix length: /12
Type: Shared address space (CGNAT) 100.64.0.0/10
Used by providers behind carrier-grade NAT (RFC 6598)
Old class: A (default /8)
As numbers: Hex 64500000 · Integer 1682964480 to 1684013055
Reverse DNS zones: 80.100.in-addr.arpa
81.100.in-addr.arpa
82.100.in-addr.arpa
83.100.in-addr.arpa
84.100.in-addr.arpa
85.100.in-addr.arpa
86.100.in-addr.arpa
87.100.in-addr.arpa
88.100.in-addr.arpa
89.100.in-addr.arpa
90.100.in-addr.arpa
91.100.in-addr.arpa
92.100.in-addr.arpa
93.100.in-addr.arpa
94.100.in-addr.arpa
95.100.in-addr.arpa
/12 is not on a 8-bit boundary, so it takes 16 /16 zones.

Binary

Binary view
	Binary (network bits bold, host bits grey)	Dotted
Address	`01100100.01010000.00000000.00000000`	`100.80.0.0`
Subnet mask	`11111111.11110000.00000000.00000000`	`255.240.0.0`
Network	`01100100.01010000.00000000.00000000`	`100.80.0.0`
Broadcast	`01100100.01011111.11111111.11111111`	`100.95.255.255`

Split into smaller subnets/19

/13 (2)/14 (4)/15 (8)/16 (16)/17 (32)/18 (64)/19 (128)/20 (256)/21 (512)/22 (1,024)/23 (2,048)/24 (4,096)

100.80.0.0/12 makes 128 subnets of /19.

Subnets
#	Subnet	Usable hosts range	Broadcast	Hosts
1	`100.80.0.0/19`	`100.80.0.1` to `100.80.31.254`	100.80.31.255	8,190
2	`100.80.32.0/19`	`100.80.32.1` to `100.80.63.254`	100.80.63.255	8,190
3	`100.80.64.0/19`	`100.80.64.1` to `100.80.95.254`	100.80.95.255	8,190
4	`100.80.96.0/19`	`100.80.96.1` to `100.80.127.254`	100.80.127.255	8,190
5	`100.80.128.0/19`	`100.80.128.1` to `100.80.159.254`	100.80.159.255	8,190
6	`100.80.160.0/19`	`100.80.160.1` to `100.80.191.254`	100.80.191.255	8,190
7	`100.80.192.0/19`	`100.80.192.1` to `100.80.223.254`	100.80.223.255	8,190
8	`100.80.224.0/19`	`100.80.224.1` to `100.80.255.254`	100.80.255.255	8,190
9	`100.81.0.0/19`	`100.81.0.1` to `100.81.31.254`	100.81.31.255	8,190
10	`100.81.32.0/19`	`100.81.32.1` to `100.81.63.254`	100.81.63.255	8,190
11	`100.81.64.0/19`	`100.81.64.1` to `100.81.95.254`	100.81.95.255	8,190
12	`100.81.96.0/19`	`100.81.96.1` to `100.81.127.254`	100.81.127.255	8,190
13	`100.81.128.0/19`	`100.81.128.1` to `100.81.159.254`	100.81.159.255	8,190
14	`100.81.160.0/19`	`100.81.160.1` to `100.81.191.254`	100.81.191.255	8,190
15	`100.81.192.0/19`	`100.81.192.1` to `100.81.223.254`	100.81.223.255	8,190
16	`100.81.224.0/19`	`100.81.224.1` to `100.81.255.254`	100.81.255.255	8,190
17	`100.82.0.0/19`	`100.82.0.1` to `100.82.31.254`	100.82.31.255	8,190
18	`100.82.32.0/19`	`100.82.32.1` to `100.82.63.254`	100.82.63.255	8,190
19	`100.82.64.0/19`	`100.82.64.1` to `100.82.95.254`	100.82.95.255	8,190
20	`100.82.96.0/19`	`100.82.96.1` to `100.82.127.254`	100.82.127.255	8,190
21	`100.82.128.0/19`	`100.82.128.1` to `100.82.159.254`	100.82.159.255	8,190
22	`100.82.160.0/19`	`100.82.160.1` to `100.82.191.254`	100.82.191.255	8,190
23	`100.82.192.0/19`	`100.82.192.1` to `100.82.223.254`	100.82.223.255	8,190
24	`100.82.224.0/19`	`100.82.224.1` to `100.82.255.254`	100.82.255.255	8,190
25	`100.83.0.0/19`	`100.83.0.1` to `100.83.31.254`	100.83.31.255	8,190
26	`100.83.32.0/19`	`100.83.32.1` to `100.83.63.254`	100.83.63.255	8,190
27	`100.83.64.0/19`	`100.83.64.1` to `100.83.95.254`	100.83.95.255	8,190
28	`100.83.96.0/19`	`100.83.96.1` to `100.83.127.254`	100.83.127.255	8,190
29	`100.83.128.0/19`	`100.83.128.1` to `100.83.159.254`	100.83.159.255	8,190
30	`100.83.160.0/19`	`100.83.160.1` to `100.83.191.254`	100.83.191.255	8,190
31	`100.83.192.0/19`	`100.83.192.1` to `100.83.223.254`	100.83.223.255	8,190
32	`100.83.224.0/19`	`100.83.224.1` to `100.83.255.254`	100.83.255.255	8,190
33	`100.84.0.0/19`	`100.84.0.1` to `100.84.31.254`	100.84.31.255	8,190
34	`100.84.32.0/19`	`100.84.32.1` to `100.84.63.254`	100.84.63.255	8,190
35	`100.84.64.0/19`	`100.84.64.1` to `100.84.95.254`	100.84.95.255	8,190
36	`100.84.96.0/19`	`100.84.96.1` to `100.84.127.254`	100.84.127.255	8,190
37	`100.84.128.0/19`	`100.84.128.1` to `100.84.159.254`	100.84.159.255	8,190
38	`100.84.160.0/19`	`100.84.160.1` to `100.84.191.254`	100.84.191.255	8,190
39	`100.84.192.0/19`	`100.84.192.1` to `100.84.223.254`	100.84.223.255	8,190
40	`100.84.224.0/19`	`100.84.224.1` to `100.84.255.254`	100.84.255.255	8,190
41	`100.85.0.0/19`	`100.85.0.1` to `100.85.31.254`	100.85.31.255	8,190
42	`100.85.32.0/19`	`100.85.32.1` to `100.85.63.254`	100.85.63.255	8,190
43	`100.85.64.0/19`	`100.85.64.1` to `100.85.95.254`	100.85.95.255	8,190
44	`100.85.96.0/19`	`100.85.96.1` to `100.85.127.254`	100.85.127.255	8,190
45	`100.85.128.0/19`	`100.85.128.1` to `100.85.159.254`	100.85.159.255	8,190
46	`100.85.160.0/19`	`100.85.160.1` to `100.85.191.254`	100.85.191.255	8,190
47	`100.85.192.0/19`	`100.85.192.1` to `100.85.223.254`	100.85.223.255	8,190
48	`100.85.224.0/19`	`100.85.224.1` to `100.85.255.254`	100.85.255.255	8,190
49	`100.86.0.0/19`	`100.86.0.1` to `100.86.31.254`	100.86.31.255	8,190
50	`100.86.32.0/19`	`100.86.32.1` to `100.86.63.254`	100.86.63.255	8,190
51	`100.86.64.0/19`	`100.86.64.1` to `100.86.95.254`	100.86.95.255	8,190
52	`100.86.96.0/19`	`100.86.96.1` to `100.86.127.254`	100.86.127.255	8,190
53	`100.86.128.0/19`	`100.86.128.1` to `100.86.159.254`	100.86.159.255	8,190
54	`100.86.160.0/19`	`100.86.160.1` to `100.86.191.254`	100.86.191.255	8,190
55	`100.86.192.0/19`	`100.86.192.1` to `100.86.223.254`	100.86.223.255	8,190
56	`100.86.224.0/19`	`100.86.224.1` to `100.86.255.254`	100.86.255.255	8,190
57	`100.87.0.0/19`	`100.87.0.1` to `100.87.31.254`	100.87.31.255	8,190
58	`100.87.32.0/19`	`100.87.32.1` to `100.87.63.254`	100.87.63.255	8,190
59	`100.87.64.0/19`	`100.87.64.1` to `100.87.95.254`	100.87.95.255	8,190
60	`100.87.96.0/19`	`100.87.96.1` to `100.87.127.254`	100.87.127.255	8,190
61	`100.87.128.0/19`	`100.87.128.1` to `100.87.159.254`	100.87.159.255	8,190
62	`100.87.160.0/19`	`100.87.160.1` to `100.87.191.254`	100.87.191.255	8,190
63	`100.87.192.0/19`	`100.87.192.1` to `100.87.223.254`	100.87.223.255	8,190
64	`100.87.224.0/19`	`100.87.224.1` to `100.87.255.254`	100.87.255.255	8,190
65	`100.88.0.0/19`	`100.88.0.1` to `100.88.31.254`	100.88.31.255	8,190
66	`100.88.32.0/19`	`100.88.32.1` to `100.88.63.254`	100.88.63.255	8,190
67	`100.88.64.0/19`	`100.88.64.1` to `100.88.95.254`	100.88.95.255	8,190
68	`100.88.96.0/19`	`100.88.96.1` to `100.88.127.254`	100.88.127.255	8,190
69	`100.88.128.0/19`	`100.88.128.1` to `100.88.159.254`	100.88.159.255	8,190
70	`100.88.160.0/19`	`100.88.160.1` to `100.88.191.254`	100.88.191.255	8,190
71	`100.88.192.0/19`	`100.88.192.1` to `100.88.223.254`	100.88.223.255	8,190
72	`100.88.224.0/19`	`100.88.224.1` to `100.88.255.254`	100.88.255.255	8,190
73	`100.89.0.0/19`	`100.89.0.1` to `100.89.31.254`	100.89.31.255	8,190
74	`100.89.32.0/19`	`100.89.32.1` to `100.89.63.254`	100.89.63.255	8,190
75	`100.89.64.0/19`	`100.89.64.1` to `100.89.95.254`	100.89.95.255	8,190
76	`100.89.96.0/19`	`100.89.96.1` to `100.89.127.254`	100.89.127.255	8,190
77	`100.89.128.0/19`	`100.89.128.1` to `100.89.159.254`	100.89.159.255	8,190
78	`100.89.160.0/19`	`100.89.160.1` to `100.89.191.254`	100.89.191.255	8,190
79	`100.89.192.0/19`	`100.89.192.1` to `100.89.223.254`	100.89.223.255	8,190
80	`100.89.224.0/19`	`100.89.224.1` to `100.89.255.254`	100.89.255.255	8,190
81	`100.90.0.0/19`	`100.90.0.1` to `100.90.31.254`	100.90.31.255	8,190
82	`100.90.32.0/19`	`100.90.32.1` to `100.90.63.254`	100.90.63.255	8,190
83	`100.90.64.0/19`	`100.90.64.1` to `100.90.95.254`	100.90.95.255	8,190
84	`100.90.96.0/19`	`100.90.96.1` to `100.90.127.254`	100.90.127.255	8,190
85	`100.90.128.0/19`	`100.90.128.1` to `100.90.159.254`	100.90.159.255	8,190
86	`100.90.160.0/19`	`100.90.160.1` to `100.90.191.254`	100.90.191.255	8,190
87	`100.90.192.0/19`	`100.90.192.1` to `100.90.223.254`	100.90.223.255	8,190
88	`100.90.224.0/19`	`100.90.224.1` to `100.90.255.254`	100.90.255.255	8,190
89	`100.91.0.0/19`	`100.91.0.1` to `100.91.31.254`	100.91.31.255	8,190
90	`100.91.32.0/19`	`100.91.32.1` to `100.91.63.254`	100.91.63.255	8,190
91	`100.91.64.0/19`	`100.91.64.1` to `100.91.95.254`	100.91.95.255	8,190
92	`100.91.96.0/19`	`100.91.96.1` to `100.91.127.254`	100.91.127.255	8,190
93	`100.91.128.0/19`	`100.91.128.1` to `100.91.159.254`	100.91.159.255	8,190
94	`100.91.160.0/19`	`100.91.160.1` to `100.91.191.254`	100.91.191.255	8,190
95	`100.91.192.0/19`	`100.91.192.1` to `100.91.223.254`	100.91.223.255	8,190
96	`100.91.224.0/19`	`100.91.224.1` to `100.91.255.254`	100.91.255.255	8,190
97	`100.92.0.0/19`	`100.92.0.1` to `100.92.31.254`	100.92.31.255	8,190
98	`100.92.32.0/19`	`100.92.32.1` to `100.92.63.254`	100.92.63.255	8,190
99	`100.92.64.0/19`	`100.92.64.1` to `100.92.95.254`	100.92.95.255	8,190
100	`100.92.96.0/19`	`100.92.96.1` to `100.92.127.254`	100.92.127.255	8,190
101	`100.92.128.0/19`	`100.92.128.1` to `100.92.159.254`	100.92.159.255	8,190
102	`100.92.160.0/19`	`100.92.160.1` to `100.92.191.254`	100.92.191.255	8,190
103	`100.92.192.0/19`	`100.92.192.1` to `100.92.223.254`	100.92.223.255	8,190
104	`100.92.224.0/19`	`100.92.224.1` to `100.92.255.254`	100.92.255.255	8,190
105	`100.93.0.0/19`	`100.93.0.1` to `100.93.31.254`	100.93.31.255	8,190
106	`100.93.32.0/19`	`100.93.32.1` to `100.93.63.254`	100.93.63.255	8,190
107	`100.93.64.0/19`	`100.93.64.1` to `100.93.95.254`	100.93.95.255	8,190
108	`100.93.96.0/19`	`100.93.96.1` to `100.93.127.254`	100.93.127.255	8,190
109	`100.93.128.0/19`	`100.93.128.1` to `100.93.159.254`	100.93.159.255	8,190
110	`100.93.160.0/19`	`100.93.160.1` to `100.93.191.254`	100.93.191.255	8,190
111	`100.93.192.0/19`	`100.93.192.1` to `100.93.223.254`	100.93.223.255	8,190
112	`100.93.224.0/19`	`100.93.224.1` to `100.93.255.254`	100.93.255.255	8,190
113	`100.94.0.0/19`	`100.94.0.1` to `100.94.31.254`	100.94.31.255	8,190
114	`100.94.32.0/19`	`100.94.32.1` to `100.94.63.254`	100.94.63.255	8,190
115	`100.94.64.0/19`	`100.94.64.1` to `100.94.95.254`	100.94.95.255	8,190
116	`100.94.96.0/19`	`100.94.96.1` to `100.94.127.254`	100.94.127.255	8,190
117	`100.94.128.0/19`	`100.94.128.1` to `100.94.159.254`	100.94.159.255	8,190
118	`100.94.160.0/19`	`100.94.160.1` to `100.94.191.254`	100.94.191.255	8,190
119	`100.94.192.0/19`	`100.94.192.1` to `100.94.223.254`	100.94.223.255	8,190
120	`100.94.224.0/19`	`100.94.224.1` to `100.94.255.254`	100.94.255.255	8,190
121	`100.95.0.0/19`	`100.95.0.1` to `100.95.31.254`	100.95.31.255	8,190
122	`100.95.32.0/19`	`100.95.32.1` to `100.95.63.254`	100.95.63.255	8,190
123	`100.95.64.0/19`	`100.95.64.1` to `100.95.95.254`	100.95.95.255	8,190
124	`100.95.96.0/19`	`100.95.96.1` to `100.95.127.254`	100.95.127.255	8,190
125	`100.95.128.0/19`	`100.95.128.1` to `100.95.159.254`	100.95.159.255	8,190
126	`100.95.160.0/19`	`100.95.160.1` to `100.95.191.254`	100.95.191.255	8,190
127	`100.95.192.0/19`	`100.95.192.1` to `100.95.223.254`	100.95.223.255	8,190
128	`100.95.224.0/19`	`100.95.224.1` to `100.95.255.254`	100.95.255.255	8,190

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)

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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

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Common questions

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