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.

Network255.9.64.0/18

Usable hosts16,382

Subnet mask255.255.192.0

Addresses16,384

Network address: 255.9.64.0
Broadcast address: 255.9.127.255
First usable: 255.9.64.1
Last usable: 255.9.127.254
Usable hosts: 16,382 (16,384 less the network and broadcast addresses)
Subnet mask: 255.255.192.0
Wildcard mask: 0.0.63.255 (Cisco ACLs, OSPF)
Prefix length: /18
Type: Reserved 240.0.0.0/4
Future use; not usable on most systems
Old class: E (reserved)
As numbers: Hex FF094000 · Integer 4278796288 to 4278812671
Reverse DNS zones: 64.9.255.in-addr.arpa
65.9.255.in-addr.arpa
66.9.255.in-addr.arpa
67.9.255.in-addr.arpa
68.9.255.in-addr.arpa
69.9.255.in-addr.arpa
70.9.255.in-addr.arpa
71.9.255.in-addr.arpa
72.9.255.in-addr.arpa
73.9.255.in-addr.arpa
74.9.255.in-addr.arpa
75.9.255.in-addr.arpa
76.9.255.in-addr.arpa
77.9.255.in-addr.arpa
78.9.255.in-addr.arpa
79.9.255.in-addr.arpa
and 48 more
/18 is not on a 8-bit boundary, so it takes 64 /24 zones.

Binary

Binary view
	Binary (network bits bold, host bits grey)	Dotted
Address	`11111111.00001001.01000000.00000000`	`255.9.64.0`
Subnet mask	`11111111.11111111.11000000.00000000`	`255.255.192.0`
Network	`11111111.00001001.01000000.00000000`	`255.9.64.0`
Broadcast	`11111111.00001001.01111111.11111111`	`255.9.127.255`

Split into smaller subnets/25

/19 (2)/20 (4)/21 (8)/22 (16)/23 (32)/24 (64)/25 (128)/26 (256)/27 (512)/28 (1,024)/29 (2,048)/30 (4,096)

255.9.64.0/18 makes 128 subnets of /25.

Subnets
#	Subnet	Usable hosts range	Broadcast	Hosts
1	`255.9.64.0/25`	`255.9.64.1` to `255.9.64.126`	255.9.64.127	126
2	`255.9.64.128/25`	`255.9.64.129` to `255.9.64.254`	255.9.64.255	126
3	`255.9.65.0/25`	`255.9.65.1` to `255.9.65.126`	255.9.65.127	126
4	`255.9.65.128/25`	`255.9.65.129` to `255.9.65.254`	255.9.65.255	126
5	`255.9.66.0/25`	`255.9.66.1` to `255.9.66.126`	255.9.66.127	126
6	`255.9.66.128/25`	`255.9.66.129` to `255.9.66.254`	255.9.66.255	126
7	`255.9.67.0/25`	`255.9.67.1` to `255.9.67.126`	255.9.67.127	126
8	`255.9.67.128/25`	`255.9.67.129` to `255.9.67.254`	255.9.67.255	126
9	`255.9.68.0/25`	`255.9.68.1` to `255.9.68.126`	255.9.68.127	126
10	`255.9.68.128/25`	`255.9.68.129` to `255.9.68.254`	255.9.68.255	126
11	`255.9.69.0/25`	`255.9.69.1` to `255.9.69.126`	255.9.69.127	126
12	`255.9.69.128/25`	`255.9.69.129` to `255.9.69.254`	255.9.69.255	126
13	`255.9.70.0/25`	`255.9.70.1` to `255.9.70.126`	255.9.70.127	126
14	`255.9.70.128/25`	`255.9.70.129` to `255.9.70.254`	255.9.70.255	126
15	`255.9.71.0/25`	`255.9.71.1` to `255.9.71.126`	255.9.71.127	126
16	`255.9.71.128/25`	`255.9.71.129` to `255.9.71.254`	255.9.71.255	126
17	`255.9.72.0/25`	`255.9.72.1` to `255.9.72.126`	255.9.72.127	126
18	`255.9.72.128/25`	`255.9.72.129` to `255.9.72.254`	255.9.72.255	126
19	`255.9.73.0/25`	`255.9.73.1` to `255.9.73.126`	255.9.73.127	126
20	`255.9.73.128/25`	`255.9.73.129` to `255.9.73.254`	255.9.73.255	126
21	`255.9.74.0/25`	`255.9.74.1` to `255.9.74.126`	255.9.74.127	126
22	`255.9.74.128/25`	`255.9.74.129` to `255.9.74.254`	255.9.74.255	126
23	`255.9.75.0/25`	`255.9.75.1` to `255.9.75.126`	255.9.75.127	126
24	`255.9.75.128/25`	`255.9.75.129` to `255.9.75.254`	255.9.75.255	126
25	`255.9.76.0/25`	`255.9.76.1` to `255.9.76.126`	255.9.76.127	126
26	`255.9.76.128/25`	`255.9.76.129` to `255.9.76.254`	255.9.76.255	126
27	`255.9.77.0/25`	`255.9.77.1` to `255.9.77.126`	255.9.77.127	126
28	`255.9.77.128/25`	`255.9.77.129` to `255.9.77.254`	255.9.77.255	126
29	`255.9.78.0/25`	`255.9.78.1` to `255.9.78.126`	255.9.78.127	126
30	`255.9.78.128/25`	`255.9.78.129` to `255.9.78.254`	255.9.78.255	126
31	`255.9.79.0/25`	`255.9.79.1` to `255.9.79.126`	255.9.79.127	126
32	`255.9.79.128/25`	`255.9.79.129` to `255.9.79.254`	255.9.79.255	126
33	`255.9.80.0/25`	`255.9.80.1` to `255.9.80.126`	255.9.80.127	126
34	`255.9.80.128/25`	`255.9.80.129` to `255.9.80.254`	255.9.80.255	126
35	`255.9.81.0/25`	`255.9.81.1` to `255.9.81.126`	255.9.81.127	126
36	`255.9.81.128/25`	`255.9.81.129` to `255.9.81.254`	255.9.81.255	126
37	`255.9.82.0/25`	`255.9.82.1` to `255.9.82.126`	255.9.82.127	126
38	`255.9.82.128/25`	`255.9.82.129` to `255.9.82.254`	255.9.82.255	126
39	`255.9.83.0/25`	`255.9.83.1` to `255.9.83.126`	255.9.83.127	126
40	`255.9.83.128/25`	`255.9.83.129` to `255.9.83.254`	255.9.83.255	126
41	`255.9.84.0/25`	`255.9.84.1` to `255.9.84.126`	255.9.84.127	126
42	`255.9.84.128/25`	`255.9.84.129` to `255.9.84.254`	255.9.84.255	126
43	`255.9.85.0/25`	`255.9.85.1` to `255.9.85.126`	255.9.85.127	126
44	`255.9.85.128/25`	`255.9.85.129` to `255.9.85.254`	255.9.85.255	126
45	`255.9.86.0/25`	`255.9.86.1` to `255.9.86.126`	255.9.86.127	126
46	`255.9.86.128/25`	`255.9.86.129` to `255.9.86.254`	255.9.86.255	126
47	`255.9.87.0/25`	`255.9.87.1` to `255.9.87.126`	255.9.87.127	126
48	`255.9.87.128/25`	`255.9.87.129` to `255.9.87.254`	255.9.87.255	126
49	`255.9.88.0/25`	`255.9.88.1` to `255.9.88.126`	255.9.88.127	126
50	`255.9.88.128/25`	`255.9.88.129` to `255.9.88.254`	255.9.88.255	126
51	`255.9.89.0/25`	`255.9.89.1` to `255.9.89.126`	255.9.89.127	126
52	`255.9.89.128/25`	`255.9.89.129` to `255.9.89.254`	255.9.89.255	126
53	`255.9.90.0/25`	`255.9.90.1` to `255.9.90.126`	255.9.90.127	126
54	`255.9.90.128/25`	`255.9.90.129` to `255.9.90.254`	255.9.90.255	126
55	`255.9.91.0/25`	`255.9.91.1` to `255.9.91.126`	255.9.91.127	126
56	`255.9.91.128/25`	`255.9.91.129` to `255.9.91.254`	255.9.91.255	126
57	`255.9.92.0/25`	`255.9.92.1` to `255.9.92.126`	255.9.92.127	126
58	`255.9.92.128/25`	`255.9.92.129` to `255.9.92.254`	255.9.92.255	126
59	`255.9.93.0/25`	`255.9.93.1` to `255.9.93.126`	255.9.93.127	126
60	`255.9.93.128/25`	`255.9.93.129` to `255.9.93.254`	255.9.93.255	126
61	`255.9.94.0/25`	`255.9.94.1` to `255.9.94.126`	255.9.94.127	126
62	`255.9.94.128/25`	`255.9.94.129` to `255.9.94.254`	255.9.94.255	126
63	`255.9.95.0/25`	`255.9.95.1` to `255.9.95.126`	255.9.95.127	126
64	`255.9.95.128/25`	`255.9.95.129` to `255.9.95.254`	255.9.95.255	126
65	`255.9.96.0/25`	`255.9.96.1` to `255.9.96.126`	255.9.96.127	126
66	`255.9.96.128/25`	`255.9.96.129` to `255.9.96.254`	255.9.96.255	126
67	`255.9.97.0/25`	`255.9.97.1` to `255.9.97.126`	255.9.97.127	126
68	`255.9.97.128/25`	`255.9.97.129` to `255.9.97.254`	255.9.97.255	126
69	`255.9.98.0/25`	`255.9.98.1` to `255.9.98.126`	255.9.98.127	126
70	`255.9.98.128/25`	`255.9.98.129` to `255.9.98.254`	255.9.98.255	126
71	`255.9.99.0/25`	`255.9.99.1` to `255.9.99.126`	255.9.99.127	126
72	`255.9.99.128/25`	`255.9.99.129` to `255.9.99.254`	255.9.99.255	126
73	`255.9.100.0/25`	`255.9.100.1` to `255.9.100.126`	255.9.100.127	126
74	`255.9.100.128/25`	`255.9.100.129` to `255.9.100.254`	255.9.100.255	126
75	`255.9.101.0/25`	`255.9.101.1` to `255.9.101.126`	255.9.101.127	126
76	`255.9.101.128/25`	`255.9.101.129` to `255.9.101.254`	255.9.101.255	126
77	`255.9.102.0/25`	`255.9.102.1` to `255.9.102.126`	255.9.102.127	126
78	`255.9.102.128/25`	`255.9.102.129` to `255.9.102.254`	255.9.102.255	126
79	`255.9.103.0/25`	`255.9.103.1` to `255.9.103.126`	255.9.103.127	126
80	`255.9.103.128/25`	`255.9.103.129` to `255.9.103.254`	255.9.103.255	126
81	`255.9.104.0/25`	`255.9.104.1` to `255.9.104.126`	255.9.104.127	126
82	`255.9.104.128/25`	`255.9.104.129` to `255.9.104.254`	255.9.104.255	126
83	`255.9.105.0/25`	`255.9.105.1` to `255.9.105.126`	255.9.105.127	126
84	`255.9.105.128/25`	`255.9.105.129` to `255.9.105.254`	255.9.105.255	126
85	`255.9.106.0/25`	`255.9.106.1` to `255.9.106.126`	255.9.106.127	126
86	`255.9.106.128/25`	`255.9.106.129` to `255.9.106.254`	255.9.106.255	126
87	`255.9.107.0/25`	`255.9.107.1` to `255.9.107.126`	255.9.107.127	126
88	`255.9.107.128/25`	`255.9.107.129` to `255.9.107.254`	255.9.107.255	126
89	`255.9.108.0/25`	`255.9.108.1` to `255.9.108.126`	255.9.108.127	126
90	`255.9.108.128/25`	`255.9.108.129` to `255.9.108.254`	255.9.108.255	126
91	`255.9.109.0/25`	`255.9.109.1` to `255.9.109.126`	255.9.109.127	126
92	`255.9.109.128/25`	`255.9.109.129` to `255.9.109.254`	255.9.109.255	126
93	`255.9.110.0/25`	`255.9.110.1` to `255.9.110.126`	255.9.110.127	126
94	`255.9.110.128/25`	`255.9.110.129` to `255.9.110.254`	255.9.110.255	126
95	`255.9.111.0/25`	`255.9.111.1` to `255.9.111.126`	255.9.111.127	126
96	`255.9.111.128/25`	`255.9.111.129` to `255.9.111.254`	255.9.111.255	126
97	`255.9.112.0/25`	`255.9.112.1` to `255.9.112.126`	255.9.112.127	126
98	`255.9.112.128/25`	`255.9.112.129` to `255.9.112.254`	255.9.112.255	126
99	`255.9.113.0/25`	`255.9.113.1` to `255.9.113.126`	255.9.113.127	126
100	`255.9.113.128/25`	`255.9.113.129` to `255.9.113.254`	255.9.113.255	126
101	`255.9.114.0/25`	`255.9.114.1` to `255.9.114.126`	255.9.114.127	126
102	`255.9.114.128/25`	`255.9.114.129` to `255.9.114.254`	255.9.114.255	126
103	`255.9.115.0/25`	`255.9.115.1` to `255.9.115.126`	255.9.115.127	126
104	`255.9.115.128/25`	`255.9.115.129` to `255.9.115.254`	255.9.115.255	126
105	`255.9.116.0/25`	`255.9.116.1` to `255.9.116.126`	255.9.116.127	126
106	`255.9.116.128/25`	`255.9.116.129` to `255.9.116.254`	255.9.116.255	126
107	`255.9.117.0/25`	`255.9.117.1` to `255.9.117.126`	255.9.117.127	126
108	`255.9.117.128/25`	`255.9.117.129` to `255.9.117.254`	255.9.117.255	126
109	`255.9.118.0/25`	`255.9.118.1` to `255.9.118.126`	255.9.118.127	126
110	`255.9.118.128/25`	`255.9.118.129` to `255.9.118.254`	255.9.118.255	126
111	`255.9.119.0/25`	`255.9.119.1` to `255.9.119.126`	255.9.119.127	126
112	`255.9.119.128/25`	`255.9.119.129` to `255.9.119.254`	255.9.119.255	126
113	`255.9.120.0/25`	`255.9.120.1` to `255.9.120.126`	255.9.120.127	126
114	`255.9.120.128/25`	`255.9.120.129` to `255.9.120.254`	255.9.120.255	126
115	`255.9.121.0/25`	`255.9.121.1` to `255.9.121.126`	255.9.121.127	126
116	`255.9.121.128/25`	`255.9.121.129` to `255.9.121.254`	255.9.121.255	126
117	`255.9.122.0/25`	`255.9.122.1` to `255.9.122.126`	255.9.122.127	126
118	`255.9.122.128/25`	`255.9.122.129` to `255.9.122.254`	255.9.122.255	126
119	`255.9.123.0/25`	`255.9.123.1` to `255.9.123.126`	255.9.123.127	126
120	`255.9.123.128/25`	`255.9.123.129` to `255.9.123.254`	255.9.123.255	126
121	`255.9.124.0/25`	`255.9.124.1` to `255.9.124.126`	255.9.124.127	126
122	`255.9.124.128/25`	`255.9.124.129` to `255.9.124.254`	255.9.124.255	126
123	`255.9.125.0/25`	`255.9.125.1` to `255.9.125.126`	255.9.125.127	126
124	`255.9.125.128/25`	`255.9.125.129` to `255.9.125.254`	255.9.125.255	126
125	`255.9.126.0/25`	`255.9.126.1` to `255.9.126.126`	255.9.126.127	126
126	`255.9.126.128/25`	`255.9.126.129` to `255.9.126.254`	255.9.126.255	126
127	`255.9.127.0/25`	`255.9.127.1` to `255.9.127.126`	255.9.127.127	126
128	`255.9.127.128/25`	`255.9.127.129` to `255.9.127.254`	255.9.127.255	126

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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