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.

Network37.131.0.0/17

Usable hosts32,766

Subnet mask255.255.128.0

Addresses32,768

Network address: 37.131.0.0
Broadcast address: 37.131.127.255
First usable: 37.131.0.1
Last usable: 37.131.127.254
Usable hosts: 32,766 (32,768 less the network and broadcast addresses)
Subnet mask: 255.255.128.0
Wildcard mask: 0.0.127.255 (Cisco ACLs, OSPF)
Prefix length: /17
Type: Public public
Old class: A (default /8)
As numbers: Hex 25830000 · Integer 629342208 to 629374975
Reverse DNS zones: 0.131.37.in-addr.arpa
1.131.37.in-addr.arpa
2.131.37.in-addr.arpa
3.131.37.in-addr.arpa
4.131.37.in-addr.arpa
5.131.37.in-addr.arpa
6.131.37.in-addr.arpa
7.131.37.in-addr.arpa
8.131.37.in-addr.arpa
9.131.37.in-addr.arpa
10.131.37.in-addr.arpa
11.131.37.in-addr.arpa
12.131.37.in-addr.arpa
13.131.37.in-addr.arpa
14.131.37.in-addr.arpa
15.131.37.in-addr.arpa
and 112 more
/17 is not on a 8-bit boundary, so it takes 128 /24 zones.

Binary

Binary view
	Binary (network bits bold, host bits grey)	Dotted
Address	`00100101.10000011.00000000.00000000`	`37.131.0.0`
Subnet mask	`11111111.11111111.10000000.00000000`	`255.255.128.0`
Network	`00100101.10000011.00000000.00000000`	`37.131.0.0`
Broadcast	`00100101.10000011.01111111.11111111`	`37.131.127.255`

Split into smaller subnets/24

/18 (2)/19 (4)/20 (8)/21 (16)/22 (32)/23 (64)/24 (128)/25 (256)/26 (512)/27 (1,024)/28 (2,048)/29 (4,096)

37.131.0.0/17 makes 128 subnets of /24.

Subnets
#	Subnet	Usable hosts range	Broadcast	Hosts
1	`37.131.0.0/24`	`37.131.0.1` to `37.131.0.254`	37.131.0.255	254
2	`37.131.1.0/24`	`37.131.1.1` to `37.131.1.254`	37.131.1.255	254
3	`37.131.2.0/24`	`37.131.2.1` to `37.131.2.254`	37.131.2.255	254
4	`37.131.3.0/24`	`37.131.3.1` to `37.131.3.254`	37.131.3.255	254
5	`37.131.4.0/24`	`37.131.4.1` to `37.131.4.254`	37.131.4.255	254
6	`37.131.5.0/24`	`37.131.5.1` to `37.131.5.254`	37.131.5.255	254
7	`37.131.6.0/24`	`37.131.6.1` to `37.131.6.254`	37.131.6.255	254
8	`37.131.7.0/24`	`37.131.7.1` to `37.131.7.254`	37.131.7.255	254
9	`37.131.8.0/24`	`37.131.8.1` to `37.131.8.254`	37.131.8.255	254
10	`37.131.9.0/24`	`37.131.9.1` to `37.131.9.254`	37.131.9.255	254
11	`37.131.10.0/24`	`37.131.10.1` to `37.131.10.254`	37.131.10.255	254
12	`37.131.11.0/24`	`37.131.11.1` to `37.131.11.254`	37.131.11.255	254
13	`37.131.12.0/24`	`37.131.12.1` to `37.131.12.254`	37.131.12.255	254
14	`37.131.13.0/24`	`37.131.13.1` to `37.131.13.254`	37.131.13.255	254
15	`37.131.14.0/24`	`37.131.14.1` to `37.131.14.254`	37.131.14.255	254
16	`37.131.15.0/24`	`37.131.15.1` to `37.131.15.254`	37.131.15.255	254
17	`37.131.16.0/24`	`37.131.16.1` to `37.131.16.254`	37.131.16.255	254
18	`37.131.17.0/24`	`37.131.17.1` to `37.131.17.254`	37.131.17.255	254
19	`37.131.18.0/24`	`37.131.18.1` to `37.131.18.254`	37.131.18.255	254
20	`37.131.19.0/24`	`37.131.19.1` to `37.131.19.254`	37.131.19.255	254
21	`37.131.20.0/24`	`37.131.20.1` to `37.131.20.254`	37.131.20.255	254
22	`37.131.21.0/24`	`37.131.21.1` to `37.131.21.254`	37.131.21.255	254
23	`37.131.22.0/24`	`37.131.22.1` to `37.131.22.254`	37.131.22.255	254
24	`37.131.23.0/24`	`37.131.23.1` to `37.131.23.254`	37.131.23.255	254
25	`37.131.24.0/24`	`37.131.24.1` to `37.131.24.254`	37.131.24.255	254
26	`37.131.25.0/24`	`37.131.25.1` to `37.131.25.254`	37.131.25.255	254
27	`37.131.26.0/24`	`37.131.26.1` to `37.131.26.254`	37.131.26.255	254
28	`37.131.27.0/24`	`37.131.27.1` to `37.131.27.254`	37.131.27.255	254
29	`37.131.28.0/24`	`37.131.28.1` to `37.131.28.254`	37.131.28.255	254
30	`37.131.29.0/24`	`37.131.29.1` to `37.131.29.254`	37.131.29.255	254
31	`37.131.30.0/24`	`37.131.30.1` to `37.131.30.254`	37.131.30.255	254
32	`37.131.31.0/24`	`37.131.31.1` to `37.131.31.254`	37.131.31.255	254
33	`37.131.32.0/24`	`37.131.32.1` to `37.131.32.254`	37.131.32.255	254
34	`37.131.33.0/24`	`37.131.33.1` to `37.131.33.254`	37.131.33.255	254
35	`37.131.34.0/24`	`37.131.34.1` to `37.131.34.254`	37.131.34.255	254
36	`37.131.35.0/24`	`37.131.35.1` to `37.131.35.254`	37.131.35.255	254
37	`37.131.36.0/24`	`37.131.36.1` to `37.131.36.254`	37.131.36.255	254
38	`37.131.37.0/24`	`37.131.37.1` to `37.131.37.254`	37.131.37.255	254
39	`37.131.38.0/24`	`37.131.38.1` to `37.131.38.254`	37.131.38.255	254
40	`37.131.39.0/24`	`37.131.39.1` to `37.131.39.254`	37.131.39.255	254
41	`37.131.40.0/24`	`37.131.40.1` to `37.131.40.254`	37.131.40.255	254
42	`37.131.41.0/24`	`37.131.41.1` to `37.131.41.254`	37.131.41.255	254
43	`37.131.42.0/24`	`37.131.42.1` to `37.131.42.254`	37.131.42.255	254
44	`37.131.43.0/24`	`37.131.43.1` to `37.131.43.254`	37.131.43.255	254
45	`37.131.44.0/24`	`37.131.44.1` to `37.131.44.254`	37.131.44.255	254
46	`37.131.45.0/24`	`37.131.45.1` to `37.131.45.254`	37.131.45.255	254
47	`37.131.46.0/24`	`37.131.46.1` to `37.131.46.254`	37.131.46.255	254
48	`37.131.47.0/24`	`37.131.47.1` to `37.131.47.254`	37.131.47.255	254
49	`37.131.48.0/24`	`37.131.48.1` to `37.131.48.254`	37.131.48.255	254
50	`37.131.49.0/24`	`37.131.49.1` to `37.131.49.254`	37.131.49.255	254
51	`37.131.50.0/24`	`37.131.50.1` to `37.131.50.254`	37.131.50.255	254
52	`37.131.51.0/24`	`37.131.51.1` to `37.131.51.254`	37.131.51.255	254
53	`37.131.52.0/24`	`37.131.52.1` to `37.131.52.254`	37.131.52.255	254
54	`37.131.53.0/24`	`37.131.53.1` to `37.131.53.254`	37.131.53.255	254
55	`37.131.54.0/24`	`37.131.54.1` to `37.131.54.254`	37.131.54.255	254
56	`37.131.55.0/24`	`37.131.55.1` to `37.131.55.254`	37.131.55.255	254
57	`37.131.56.0/24`	`37.131.56.1` to `37.131.56.254`	37.131.56.255	254
58	`37.131.57.0/24`	`37.131.57.1` to `37.131.57.254`	37.131.57.255	254
59	`37.131.58.0/24`	`37.131.58.1` to `37.131.58.254`	37.131.58.255	254
60	`37.131.59.0/24`	`37.131.59.1` to `37.131.59.254`	37.131.59.255	254
61	`37.131.60.0/24`	`37.131.60.1` to `37.131.60.254`	37.131.60.255	254
62	`37.131.61.0/24`	`37.131.61.1` to `37.131.61.254`	37.131.61.255	254
63	`37.131.62.0/24`	`37.131.62.1` to `37.131.62.254`	37.131.62.255	254
64	`37.131.63.0/24`	`37.131.63.1` to `37.131.63.254`	37.131.63.255	254
65	`37.131.64.0/24`	`37.131.64.1` to `37.131.64.254`	37.131.64.255	254
66	`37.131.65.0/24`	`37.131.65.1` to `37.131.65.254`	37.131.65.255	254
67	`37.131.66.0/24`	`37.131.66.1` to `37.131.66.254`	37.131.66.255	254
68	`37.131.67.0/24`	`37.131.67.1` to `37.131.67.254`	37.131.67.255	254
69	`37.131.68.0/24`	`37.131.68.1` to `37.131.68.254`	37.131.68.255	254
70	`37.131.69.0/24`	`37.131.69.1` to `37.131.69.254`	37.131.69.255	254
71	`37.131.70.0/24`	`37.131.70.1` to `37.131.70.254`	37.131.70.255	254
72	`37.131.71.0/24`	`37.131.71.1` to `37.131.71.254`	37.131.71.255	254
73	`37.131.72.0/24`	`37.131.72.1` to `37.131.72.254`	37.131.72.255	254
74	`37.131.73.0/24`	`37.131.73.1` to `37.131.73.254`	37.131.73.255	254
75	`37.131.74.0/24`	`37.131.74.1` to `37.131.74.254`	37.131.74.255	254
76	`37.131.75.0/24`	`37.131.75.1` to `37.131.75.254`	37.131.75.255	254
77	`37.131.76.0/24`	`37.131.76.1` to `37.131.76.254`	37.131.76.255	254
78	`37.131.77.0/24`	`37.131.77.1` to `37.131.77.254`	37.131.77.255	254
79	`37.131.78.0/24`	`37.131.78.1` to `37.131.78.254`	37.131.78.255	254
80	`37.131.79.0/24`	`37.131.79.1` to `37.131.79.254`	37.131.79.255	254
81	`37.131.80.0/24`	`37.131.80.1` to `37.131.80.254`	37.131.80.255	254
82	`37.131.81.0/24`	`37.131.81.1` to `37.131.81.254`	37.131.81.255	254
83	`37.131.82.0/24`	`37.131.82.1` to `37.131.82.254`	37.131.82.255	254
84	`37.131.83.0/24`	`37.131.83.1` to `37.131.83.254`	37.131.83.255	254
85	`37.131.84.0/24`	`37.131.84.1` to `37.131.84.254`	37.131.84.255	254
86	`37.131.85.0/24`	`37.131.85.1` to `37.131.85.254`	37.131.85.255	254
87	`37.131.86.0/24`	`37.131.86.1` to `37.131.86.254`	37.131.86.255	254
88	`37.131.87.0/24`	`37.131.87.1` to `37.131.87.254`	37.131.87.255	254
89	`37.131.88.0/24`	`37.131.88.1` to `37.131.88.254`	37.131.88.255	254
90	`37.131.89.0/24`	`37.131.89.1` to `37.131.89.254`	37.131.89.255	254
91	`37.131.90.0/24`	`37.131.90.1` to `37.131.90.254`	37.131.90.255	254
92	`37.131.91.0/24`	`37.131.91.1` to `37.131.91.254`	37.131.91.255	254
93	`37.131.92.0/24`	`37.131.92.1` to `37.131.92.254`	37.131.92.255	254
94	`37.131.93.0/24`	`37.131.93.1` to `37.131.93.254`	37.131.93.255	254
95	`37.131.94.0/24`	`37.131.94.1` to `37.131.94.254`	37.131.94.255	254
96	`37.131.95.0/24`	`37.131.95.1` to `37.131.95.254`	37.131.95.255	254
97	`37.131.96.0/24`	`37.131.96.1` to `37.131.96.254`	37.131.96.255	254
98	`37.131.97.0/24`	`37.131.97.1` to `37.131.97.254`	37.131.97.255	254
99	`37.131.98.0/24`	`37.131.98.1` to `37.131.98.254`	37.131.98.255	254
100	`37.131.99.0/24`	`37.131.99.1` to `37.131.99.254`	37.131.99.255	254
101	`37.131.100.0/24`	`37.131.100.1` to `37.131.100.254`	37.131.100.255	254
102	`37.131.101.0/24`	`37.131.101.1` to `37.131.101.254`	37.131.101.255	254
103	`37.131.102.0/24`	`37.131.102.1` to `37.131.102.254`	37.131.102.255	254
104	`37.131.103.0/24`	`37.131.103.1` to `37.131.103.254`	37.131.103.255	254
105	`37.131.104.0/24`	`37.131.104.1` to `37.131.104.254`	37.131.104.255	254
106	`37.131.105.0/24`	`37.131.105.1` to `37.131.105.254`	37.131.105.255	254
107	`37.131.106.0/24`	`37.131.106.1` to `37.131.106.254`	37.131.106.255	254
108	`37.131.107.0/24`	`37.131.107.1` to `37.131.107.254`	37.131.107.255	254
109	`37.131.108.0/24`	`37.131.108.1` to `37.131.108.254`	37.131.108.255	254
110	`37.131.109.0/24`	`37.131.109.1` to `37.131.109.254`	37.131.109.255	254
111	`37.131.110.0/24`	`37.131.110.1` to `37.131.110.254`	37.131.110.255	254
112	`37.131.111.0/24`	`37.131.111.1` to `37.131.111.254`	37.131.111.255	254
113	`37.131.112.0/24`	`37.131.112.1` to `37.131.112.254`	37.131.112.255	254
114	`37.131.113.0/24`	`37.131.113.1` to `37.131.113.254`	37.131.113.255	254
115	`37.131.114.0/24`	`37.131.114.1` to `37.131.114.254`	37.131.114.255	254
116	`37.131.115.0/24`	`37.131.115.1` to `37.131.115.254`	37.131.115.255	254
117	`37.131.116.0/24`	`37.131.116.1` to `37.131.116.254`	37.131.116.255	254
118	`37.131.117.0/24`	`37.131.117.1` to `37.131.117.254`	37.131.117.255	254
119	`37.131.118.0/24`	`37.131.118.1` to `37.131.118.254`	37.131.118.255	254
120	`37.131.119.0/24`	`37.131.119.1` to `37.131.119.254`	37.131.119.255	254
121	`37.131.120.0/24`	`37.131.120.1` to `37.131.120.254`	37.131.120.255	254
122	`37.131.121.0/24`	`37.131.121.1` to `37.131.121.254`	37.131.121.255	254
123	`37.131.122.0/24`	`37.131.122.1` to `37.131.122.254`	37.131.122.255	254
124	`37.131.123.0/24`	`37.131.123.1` to `37.131.123.254`	37.131.123.255	254
125	`37.131.124.0/24`	`37.131.124.1` to `37.131.124.254`	37.131.124.255	254
126	`37.131.125.0/24`	`37.131.125.1` to `37.131.125.254`	37.131.125.255	254
127	`37.131.126.0/24`	`37.131.126.1` to `37.131.126.254`	37.131.126.255	254
128	`37.131.127.0/24`	`37.131.127.1` to `37.131.127.254`	37.131.127.255	254

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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