Speed and call quality testMy IP addressIP subnet calculatorDNS reportWhoIs lookupRemote support

Internet and network

Speed and call quality testTest delay, jitter and speed, with a focus on phone calls.My IP addressYour public IPv4 and IPv6 addresses, provider and address range.WhoIs lookupWho owns a domain or IP address, when it expires, and its DNS.DNS reportEvery DNS record for a domain, with email setup checked.IP subnet calculatorWork out a network's range, mask and hosts, and split it into subnets.

Computers and devices

Update checkIs this computer, phone and browser up to date? With links to update.Camera and mic testCheck your webcam and microphone before a call.Test print pagePrint an A4 page to check a printer: edges, text, line art and colours.

Make and print

Clean textStrip hidden characters, smart quotes and odd spaces from pasted text.QR code makerMake a QR code for a link, contact or message. Nothing leaves your browser.Wi-Fi QR posterPrint an A4 poster that lets guests join your Wi-Fi by scanning.

Surftec support

Remote supportLet a Surftec engineer connect to your computer to help you.All workingA full-screen confirmation that everything is up and running.

Surftec

Surftec websiteServices, news and how to contact Surftec
Cloud Tools
Guest
GuestNot signed in

Surftec customers will be recognised automatically when they use these tools from their office network.

Customer sign-in is coming soon.

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.

Network51.2.192.0/18
Usable hosts16,382
Subnet mask255.255.192.0
Addresses16,384
Network address
51.2.192.0
Broadcast address
51.2.255.255
First usable
51.2.192.1
Last usable
51.2.255.254
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
Public public
Old class
A (default /8)
As numbers
Hex 3302C000 · Integer 855818240 to 855834623
Reverse DNS zones
192.2.51.in-addr.arpa
193.2.51.in-addr.arpa
194.2.51.in-addr.arpa
195.2.51.in-addr.arpa
196.2.51.in-addr.arpa
197.2.51.in-addr.arpa
198.2.51.in-addr.arpa
199.2.51.in-addr.arpa
200.2.51.in-addr.arpa
201.2.51.in-addr.arpa
202.2.51.in-addr.arpa
203.2.51.in-addr.arpa
204.2.51.in-addr.arpa
205.2.51.in-addr.arpa
206.2.51.in-addr.arpa
207.2.51.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
Address00110011.00000010.11000000.0000000051.2.192.0
Subnet mask11111111.11111111.11000000.00000000255.255.192.0
Network00110011.00000010.11000000.0000000051.2.192.0
Broadcast00110011.00000010.11111111.1111111151.2.255.255
Split into smaller subnets/26
/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)

51.2.192.0/18 makes 256 subnets of /26.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
151.2.192.0/2651.2.192.1 to 51.2.192.6251.2.192.6362
251.2.192.64/2651.2.192.65 to 51.2.192.12651.2.192.12762
351.2.192.128/2651.2.192.129 to 51.2.192.19051.2.192.19162
451.2.192.192/2651.2.192.193 to 51.2.192.25451.2.192.25562
551.2.193.0/2651.2.193.1 to 51.2.193.6251.2.193.6362
651.2.193.64/2651.2.193.65 to 51.2.193.12651.2.193.12762
751.2.193.128/2651.2.193.129 to 51.2.193.19051.2.193.19162
851.2.193.192/2651.2.193.193 to 51.2.193.25451.2.193.25562
951.2.194.0/2651.2.194.1 to 51.2.194.6251.2.194.6362
1051.2.194.64/2651.2.194.65 to 51.2.194.12651.2.194.12762
1151.2.194.128/2651.2.194.129 to 51.2.194.19051.2.194.19162
1251.2.194.192/2651.2.194.193 to 51.2.194.25451.2.194.25562
1351.2.195.0/2651.2.195.1 to 51.2.195.6251.2.195.6362
1451.2.195.64/2651.2.195.65 to 51.2.195.12651.2.195.12762
1551.2.195.128/2651.2.195.129 to 51.2.195.19051.2.195.19162
1651.2.195.192/2651.2.195.193 to 51.2.195.25451.2.195.25562
1751.2.196.0/2651.2.196.1 to 51.2.196.6251.2.196.6362
1851.2.196.64/2651.2.196.65 to 51.2.196.12651.2.196.12762
1951.2.196.128/2651.2.196.129 to 51.2.196.19051.2.196.19162
2051.2.196.192/2651.2.196.193 to 51.2.196.25451.2.196.25562
2151.2.197.0/2651.2.197.1 to 51.2.197.6251.2.197.6362
2251.2.197.64/2651.2.197.65 to 51.2.197.12651.2.197.12762
2351.2.197.128/2651.2.197.129 to 51.2.197.19051.2.197.19162
2451.2.197.192/2651.2.197.193 to 51.2.197.25451.2.197.25562
2551.2.198.0/2651.2.198.1 to 51.2.198.6251.2.198.6362
2651.2.198.64/2651.2.198.65 to 51.2.198.12651.2.198.12762
2751.2.198.128/2651.2.198.129 to 51.2.198.19051.2.198.19162
2851.2.198.192/2651.2.198.193 to 51.2.198.25451.2.198.25562
2951.2.199.0/2651.2.199.1 to 51.2.199.6251.2.199.6362
3051.2.199.64/2651.2.199.65 to 51.2.199.12651.2.199.12762
3151.2.199.128/2651.2.199.129 to 51.2.199.19051.2.199.19162
3251.2.199.192/2651.2.199.193 to 51.2.199.25451.2.199.25562
3351.2.200.0/2651.2.200.1 to 51.2.200.6251.2.200.6362
3451.2.200.64/2651.2.200.65 to 51.2.200.12651.2.200.12762
3551.2.200.128/2651.2.200.129 to 51.2.200.19051.2.200.19162
3651.2.200.192/2651.2.200.193 to 51.2.200.25451.2.200.25562
3751.2.201.0/2651.2.201.1 to 51.2.201.6251.2.201.6362
3851.2.201.64/2651.2.201.65 to 51.2.201.12651.2.201.12762
3951.2.201.128/2651.2.201.129 to 51.2.201.19051.2.201.19162
4051.2.201.192/2651.2.201.193 to 51.2.201.25451.2.201.25562
4151.2.202.0/2651.2.202.1 to 51.2.202.6251.2.202.6362
4251.2.202.64/2651.2.202.65 to 51.2.202.12651.2.202.12762
4351.2.202.128/2651.2.202.129 to 51.2.202.19051.2.202.19162
4451.2.202.192/2651.2.202.193 to 51.2.202.25451.2.202.25562
4551.2.203.0/2651.2.203.1 to 51.2.203.6251.2.203.6362
4651.2.203.64/2651.2.203.65 to 51.2.203.12651.2.203.12762
4751.2.203.128/2651.2.203.129 to 51.2.203.19051.2.203.19162
4851.2.203.192/2651.2.203.193 to 51.2.203.25451.2.203.25562
4951.2.204.0/2651.2.204.1 to 51.2.204.6251.2.204.6362
5051.2.204.64/2651.2.204.65 to 51.2.204.12651.2.204.12762
5151.2.204.128/2651.2.204.129 to 51.2.204.19051.2.204.19162
5251.2.204.192/2651.2.204.193 to 51.2.204.25451.2.204.25562
5351.2.205.0/2651.2.205.1 to 51.2.205.6251.2.205.6362
5451.2.205.64/2651.2.205.65 to 51.2.205.12651.2.205.12762
5551.2.205.128/2651.2.205.129 to 51.2.205.19051.2.205.19162
5651.2.205.192/2651.2.205.193 to 51.2.205.25451.2.205.25562
5751.2.206.0/2651.2.206.1 to 51.2.206.6251.2.206.6362
5851.2.206.64/2651.2.206.65 to 51.2.206.12651.2.206.12762
5951.2.206.128/2651.2.206.129 to 51.2.206.19051.2.206.19162
6051.2.206.192/2651.2.206.193 to 51.2.206.25451.2.206.25562
6151.2.207.0/2651.2.207.1 to 51.2.207.6251.2.207.6362
6251.2.207.64/2651.2.207.65 to 51.2.207.12651.2.207.12762
6351.2.207.128/2651.2.207.129 to 51.2.207.19051.2.207.19162
6451.2.207.192/2651.2.207.193 to 51.2.207.25451.2.207.25562
6551.2.208.0/2651.2.208.1 to 51.2.208.6251.2.208.6362
6651.2.208.64/2651.2.208.65 to 51.2.208.12651.2.208.12762
6751.2.208.128/2651.2.208.129 to 51.2.208.19051.2.208.19162
6851.2.208.192/2651.2.208.193 to 51.2.208.25451.2.208.25562
6951.2.209.0/2651.2.209.1 to 51.2.209.6251.2.209.6362
7051.2.209.64/2651.2.209.65 to 51.2.209.12651.2.209.12762
7151.2.209.128/2651.2.209.129 to 51.2.209.19051.2.209.19162
7251.2.209.192/2651.2.209.193 to 51.2.209.25451.2.209.25562
7351.2.210.0/2651.2.210.1 to 51.2.210.6251.2.210.6362
7451.2.210.64/2651.2.210.65 to 51.2.210.12651.2.210.12762
7551.2.210.128/2651.2.210.129 to 51.2.210.19051.2.210.19162
7651.2.210.192/2651.2.210.193 to 51.2.210.25451.2.210.25562
7751.2.211.0/2651.2.211.1 to 51.2.211.6251.2.211.6362
7851.2.211.64/2651.2.211.65 to 51.2.211.12651.2.211.12762
7951.2.211.128/2651.2.211.129 to 51.2.211.19051.2.211.19162
8051.2.211.192/2651.2.211.193 to 51.2.211.25451.2.211.25562
8151.2.212.0/2651.2.212.1 to 51.2.212.6251.2.212.6362
8251.2.212.64/2651.2.212.65 to 51.2.212.12651.2.212.12762
8351.2.212.128/2651.2.212.129 to 51.2.212.19051.2.212.19162
8451.2.212.192/2651.2.212.193 to 51.2.212.25451.2.212.25562
8551.2.213.0/2651.2.213.1 to 51.2.213.6251.2.213.6362
8651.2.213.64/2651.2.213.65 to 51.2.213.12651.2.213.12762
8751.2.213.128/2651.2.213.129 to 51.2.213.19051.2.213.19162
8851.2.213.192/2651.2.213.193 to 51.2.213.25451.2.213.25562
8951.2.214.0/2651.2.214.1 to 51.2.214.6251.2.214.6362
9051.2.214.64/2651.2.214.65 to 51.2.214.12651.2.214.12762
9151.2.214.128/2651.2.214.129 to 51.2.214.19051.2.214.19162
9251.2.214.192/2651.2.214.193 to 51.2.214.25451.2.214.25562
9351.2.215.0/2651.2.215.1 to 51.2.215.6251.2.215.6362
9451.2.215.64/2651.2.215.65 to 51.2.215.12651.2.215.12762
9551.2.215.128/2651.2.215.129 to 51.2.215.19051.2.215.19162
9651.2.215.192/2651.2.215.193 to 51.2.215.25451.2.215.25562
9751.2.216.0/2651.2.216.1 to 51.2.216.6251.2.216.6362
9851.2.216.64/2651.2.216.65 to 51.2.216.12651.2.216.12762
9951.2.216.128/2651.2.216.129 to 51.2.216.19051.2.216.19162
10051.2.216.192/2651.2.216.193 to 51.2.216.25451.2.216.25562
10151.2.217.0/2651.2.217.1 to 51.2.217.6251.2.217.6362
10251.2.217.64/2651.2.217.65 to 51.2.217.12651.2.217.12762
10351.2.217.128/2651.2.217.129 to 51.2.217.19051.2.217.19162
10451.2.217.192/2651.2.217.193 to 51.2.217.25451.2.217.25562
10551.2.218.0/2651.2.218.1 to 51.2.218.6251.2.218.6362
10651.2.218.64/2651.2.218.65 to 51.2.218.12651.2.218.12762
10751.2.218.128/2651.2.218.129 to 51.2.218.19051.2.218.19162
10851.2.218.192/2651.2.218.193 to 51.2.218.25451.2.218.25562
10951.2.219.0/2651.2.219.1 to 51.2.219.6251.2.219.6362
11051.2.219.64/2651.2.219.65 to 51.2.219.12651.2.219.12762
11151.2.219.128/2651.2.219.129 to 51.2.219.19051.2.219.19162
11251.2.219.192/2651.2.219.193 to 51.2.219.25451.2.219.25562
11351.2.220.0/2651.2.220.1 to 51.2.220.6251.2.220.6362
11451.2.220.64/2651.2.220.65 to 51.2.220.12651.2.220.12762
11551.2.220.128/2651.2.220.129 to 51.2.220.19051.2.220.19162
11651.2.220.192/2651.2.220.193 to 51.2.220.25451.2.220.25562
11751.2.221.0/2651.2.221.1 to 51.2.221.6251.2.221.6362
11851.2.221.64/2651.2.221.65 to 51.2.221.12651.2.221.12762
11951.2.221.128/2651.2.221.129 to 51.2.221.19051.2.221.19162
12051.2.221.192/2651.2.221.193 to 51.2.221.25451.2.221.25562
12151.2.222.0/2651.2.222.1 to 51.2.222.6251.2.222.6362
12251.2.222.64/2651.2.222.65 to 51.2.222.12651.2.222.12762
12351.2.222.128/2651.2.222.129 to 51.2.222.19051.2.222.19162
12451.2.222.192/2651.2.222.193 to 51.2.222.25451.2.222.25562
12551.2.223.0/2651.2.223.1 to 51.2.223.6251.2.223.6362
12651.2.223.64/2651.2.223.65 to 51.2.223.12651.2.223.12762
12751.2.223.128/2651.2.223.129 to 51.2.223.19051.2.223.19162
12851.2.223.192/2651.2.223.193 to 51.2.223.25451.2.223.25562
12951.2.224.0/2651.2.224.1 to 51.2.224.6251.2.224.6362
13051.2.224.64/2651.2.224.65 to 51.2.224.12651.2.224.12762
13151.2.224.128/2651.2.224.129 to 51.2.224.19051.2.224.19162
13251.2.224.192/2651.2.224.193 to 51.2.224.25451.2.224.25562
13351.2.225.0/2651.2.225.1 to 51.2.225.6251.2.225.6362
13451.2.225.64/2651.2.225.65 to 51.2.225.12651.2.225.12762
13551.2.225.128/2651.2.225.129 to 51.2.225.19051.2.225.19162
13651.2.225.192/2651.2.225.193 to 51.2.225.25451.2.225.25562
13751.2.226.0/2651.2.226.1 to 51.2.226.6251.2.226.6362
13851.2.226.64/2651.2.226.65 to 51.2.226.12651.2.226.12762
13951.2.226.128/2651.2.226.129 to 51.2.226.19051.2.226.19162
14051.2.226.192/2651.2.226.193 to 51.2.226.25451.2.226.25562
14151.2.227.0/2651.2.227.1 to 51.2.227.6251.2.227.6362
14251.2.227.64/2651.2.227.65 to 51.2.227.12651.2.227.12762
14351.2.227.128/2651.2.227.129 to 51.2.227.19051.2.227.19162
14451.2.227.192/2651.2.227.193 to 51.2.227.25451.2.227.25562
14551.2.228.0/2651.2.228.1 to 51.2.228.6251.2.228.6362
14651.2.228.64/2651.2.228.65 to 51.2.228.12651.2.228.12762
14751.2.228.128/2651.2.228.129 to 51.2.228.19051.2.228.19162
14851.2.228.192/2651.2.228.193 to 51.2.228.25451.2.228.25562
14951.2.229.0/2651.2.229.1 to 51.2.229.6251.2.229.6362
15051.2.229.64/2651.2.229.65 to 51.2.229.12651.2.229.12762
15151.2.229.128/2651.2.229.129 to 51.2.229.19051.2.229.19162
15251.2.229.192/2651.2.229.193 to 51.2.229.25451.2.229.25562
15351.2.230.0/2651.2.230.1 to 51.2.230.6251.2.230.6362
15451.2.230.64/2651.2.230.65 to 51.2.230.12651.2.230.12762
15551.2.230.128/2651.2.230.129 to 51.2.230.19051.2.230.19162
15651.2.230.192/2651.2.230.193 to 51.2.230.25451.2.230.25562
15751.2.231.0/2651.2.231.1 to 51.2.231.6251.2.231.6362
15851.2.231.64/2651.2.231.65 to 51.2.231.12651.2.231.12762
15951.2.231.128/2651.2.231.129 to 51.2.231.19051.2.231.19162
16051.2.231.192/2651.2.231.193 to 51.2.231.25451.2.231.25562
16151.2.232.0/2651.2.232.1 to 51.2.232.6251.2.232.6362
16251.2.232.64/2651.2.232.65 to 51.2.232.12651.2.232.12762
16351.2.232.128/2651.2.232.129 to 51.2.232.19051.2.232.19162
16451.2.232.192/2651.2.232.193 to 51.2.232.25451.2.232.25562
16551.2.233.0/2651.2.233.1 to 51.2.233.6251.2.233.6362
16651.2.233.64/2651.2.233.65 to 51.2.233.12651.2.233.12762
16751.2.233.128/2651.2.233.129 to 51.2.233.19051.2.233.19162
16851.2.233.192/2651.2.233.193 to 51.2.233.25451.2.233.25562
16951.2.234.0/2651.2.234.1 to 51.2.234.6251.2.234.6362
17051.2.234.64/2651.2.234.65 to 51.2.234.12651.2.234.12762
17151.2.234.128/2651.2.234.129 to 51.2.234.19051.2.234.19162
17251.2.234.192/2651.2.234.193 to 51.2.234.25451.2.234.25562
17351.2.235.0/2651.2.235.1 to 51.2.235.6251.2.235.6362
17451.2.235.64/2651.2.235.65 to 51.2.235.12651.2.235.12762
17551.2.235.128/2651.2.235.129 to 51.2.235.19051.2.235.19162
17651.2.235.192/2651.2.235.193 to 51.2.235.25451.2.235.25562
17751.2.236.0/2651.2.236.1 to 51.2.236.6251.2.236.6362
17851.2.236.64/2651.2.236.65 to 51.2.236.12651.2.236.12762
17951.2.236.128/2651.2.236.129 to 51.2.236.19051.2.236.19162
18051.2.236.192/2651.2.236.193 to 51.2.236.25451.2.236.25562
18151.2.237.0/2651.2.237.1 to 51.2.237.6251.2.237.6362
18251.2.237.64/2651.2.237.65 to 51.2.237.12651.2.237.12762
18351.2.237.128/2651.2.237.129 to 51.2.237.19051.2.237.19162
18451.2.237.192/2651.2.237.193 to 51.2.237.25451.2.237.25562
18551.2.238.0/2651.2.238.1 to 51.2.238.6251.2.238.6362
18651.2.238.64/2651.2.238.65 to 51.2.238.12651.2.238.12762
18751.2.238.128/2651.2.238.129 to 51.2.238.19051.2.238.19162
18851.2.238.192/2651.2.238.193 to 51.2.238.25451.2.238.25562
18951.2.239.0/2651.2.239.1 to 51.2.239.6251.2.239.6362
19051.2.239.64/2651.2.239.65 to 51.2.239.12651.2.239.12762
19151.2.239.128/2651.2.239.129 to 51.2.239.19051.2.239.19162
19251.2.239.192/2651.2.239.193 to 51.2.239.25451.2.239.25562
19351.2.240.0/2651.2.240.1 to 51.2.240.6251.2.240.6362
19451.2.240.64/2651.2.240.65 to 51.2.240.12651.2.240.12762
19551.2.240.128/2651.2.240.129 to 51.2.240.19051.2.240.19162
19651.2.240.192/2651.2.240.193 to 51.2.240.25451.2.240.25562
19751.2.241.0/2651.2.241.1 to 51.2.241.6251.2.241.6362
19851.2.241.64/2651.2.241.65 to 51.2.241.12651.2.241.12762
19951.2.241.128/2651.2.241.129 to 51.2.241.19051.2.241.19162
20051.2.241.192/2651.2.241.193 to 51.2.241.25451.2.241.25562
20151.2.242.0/2651.2.242.1 to 51.2.242.6251.2.242.6362
20251.2.242.64/2651.2.242.65 to 51.2.242.12651.2.242.12762
20351.2.242.128/2651.2.242.129 to 51.2.242.19051.2.242.19162
20451.2.242.192/2651.2.242.193 to 51.2.242.25451.2.242.25562
20551.2.243.0/2651.2.243.1 to 51.2.243.6251.2.243.6362
20651.2.243.64/2651.2.243.65 to 51.2.243.12651.2.243.12762
20751.2.243.128/2651.2.243.129 to 51.2.243.19051.2.243.19162
20851.2.243.192/2651.2.243.193 to 51.2.243.25451.2.243.25562
20951.2.244.0/2651.2.244.1 to 51.2.244.6251.2.244.6362
21051.2.244.64/2651.2.244.65 to 51.2.244.12651.2.244.12762
21151.2.244.128/2651.2.244.129 to 51.2.244.19051.2.244.19162
21251.2.244.192/2651.2.244.193 to 51.2.244.25451.2.244.25562
21351.2.245.0/2651.2.245.1 to 51.2.245.6251.2.245.6362
21451.2.245.64/2651.2.245.65 to 51.2.245.12651.2.245.12762
21551.2.245.128/2651.2.245.129 to 51.2.245.19051.2.245.19162
21651.2.245.192/2651.2.245.193 to 51.2.245.25451.2.245.25562
21751.2.246.0/2651.2.246.1 to 51.2.246.6251.2.246.6362
21851.2.246.64/2651.2.246.65 to 51.2.246.12651.2.246.12762
21951.2.246.128/2651.2.246.129 to 51.2.246.19051.2.246.19162
22051.2.246.192/2651.2.246.193 to 51.2.246.25451.2.246.25562
22151.2.247.0/2651.2.247.1 to 51.2.247.6251.2.247.6362
22251.2.247.64/2651.2.247.65 to 51.2.247.12651.2.247.12762
22351.2.247.128/2651.2.247.129 to 51.2.247.19051.2.247.19162
22451.2.247.192/2651.2.247.193 to 51.2.247.25451.2.247.25562
22551.2.248.0/2651.2.248.1 to 51.2.248.6251.2.248.6362
22651.2.248.64/2651.2.248.65 to 51.2.248.12651.2.248.12762
22751.2.248.128/2651.2.248.129 to 51.2.248.19051.2.248.19162
22851.2.248.192/2651.2.248.193 to 51.2.248.25451.2.248.25562
22951.2.249.0/2651.2.249.1 to 51.2.249.6251.2.249.6362
23051.2.249.64/2651.2.249.65 to 51.2.249.12651.2.249.12762
23151.2.249.128/2651.2.249.129 to 51.2.249.19051.2.249.19162
23251.2.249.192/2651.2.249.193 to 51.2.249.25451.2.249.25562
23351.2.250.0/2651.2.250.1 to 51.2.250.6251.2.250.6362
23451.2.250.64/2651.2.250.65 to 51.2.250.12651.2.250.12762
23551.2.250.128/2651.2.250.129 to 51.2.250.19051.2.250.19162
23651.2.250.192/2651.2.250.193 to 51.2.250.25451.2.250.25562
23751.2.251.0/2651.2.251.1 to 51.2.251.6251.2.251.6362
23851.2.251.64/2651.2.251.65 to 51.2.251.12651.2.251.12762
23951.2.251.128/2651.2.251.129 to 51.2.251.19051.2.251.19162
24051.2.251.192/2651.2.251.193 to 51.2.251.25451.2.251.25562
24151.2.252.0/2651.2.252.1 to 51.2.252.6251.2.252.6362
24251.2.252.64/2651.2.252.65 to 51.2.252.12651.2.252.12762
24351.2.252.128/2651.2.252.129 to 51.2.252.19051.2.252.19162
24451.2.252.192/2651.2.252.193 to 51.2.252.25451.2.252.25562
24551.2.253.0/2651.2.253.1 to 51.2.253.6251.2.253.6362
24651.2.253.64/2651.2.253.65 to 51.2.253.12651.2.253.12762
24751.2.253.128/2651.2.253.129 to 51.2.253.19051.2.253.19162
24851.2.253.192/2651.2.253.193 to 51.2.253.25451.2.253.25562
24951.2.254.0/2651.2.254.1 to 51.2.254.6251.2.254.6362
25051.2.254.64/2651.2.254.65 to 51.2.254.12651.2.254.12762
25151.2.254.128/2651.2.254.129 to 51.2.254.19051.2.254.19162
25251.2.254.192/2651.2.254.193 to 51.2.254.25451.2.254.25562
25351.2.255.0/2651.2.255.1 to 51.2.255.6251.2.255.6362
25451.2.255.64/2651.2.255.65 to 51.2.255.12651.2.255.12762
25551.2.255.128/2651.2.255.129 to 51.2.255.19051.2.255.19162
25651.2.255.192/2651.2.255.193 to 51.2.255.25451.2.255.25562

IPv4 CIDR reference (/0 to /32)

IPv4 prefix lengths
PrefixSubnet maskWildcardAddressesUsable hostsSizeTypical use
/00.0.0.0255.255.255.2554,294,967,2964,294,967,29416,777,216 × /24
/1128.0.0.0127.255.255.2552,147,483,6482,147,483,6468,388,608 × /24
/2192.0.0.063.255.255.2551,073,741,8241,073,741,8224,194,304 × /24
/3224.0.0.031.255.255.255536,870,912536,870,9102,097,152 × /24
/4240.0.0.015.255.255.255268,435,456268,435,4541,048,576 × /24
/5248.0.0.07.255.255.255134,217,728134,217,726524,288 × /24
/6252.0.0.03.255.255.25567,108,86467,108,862262,144 × /24
/7254.0.0.01.255.255.25533,554,43233,554,430131,072 × /24
/8255.0.0.00.255.255.25516,777,21616,777,21465,536 × /24Old class A; 10.0.0.0/8
/9255.128.0.00.127.255.2558,388,6088,388,60632,768 × /24
/10255.192.0.00.63.255.2554,194,3044,194,30216,384 × /24
/11255.224.0.00.31.255.2552,097,1522,097,1508,192 × /24
/12255.240.0.00.15.255.2551,048,5761,048,5744,096 × /24172.16.0.0/12
/13255.248.0.00.7.255.255524,288524,2862,048 × /24
/14255.252.0.00.3.255.255262,144262,1421,024 × /24
/15255.254.0.00.1.255.255131,072131,070512 × /24
/16255.255.0.00.0.255.25565,53665,534256 × /24Old class B; 192.168.0.0/16
/17255.255.128.00.0.127.25532,76832,766128 × /24
/18255.255.192.00.0.63.25516,38416,38264 × /24
/19255.255.224.00.0.31.2558,1928,19032 × /24
/20255.255.240.00.0.15.2554,0964,09416 × /24
/21255.255.248.00.0.7.2552,0482,0468 × /24
/22255.255.252.00.0.3.2551,0241,0224 × /24Large office or guest Wi-Fi (1,022 hosts)
/23255.255.254.00.0.1.2555125102 × /24Larger office LAN (510 hosts)
/24255.255.255.00.0.0.2552562541 × /24Typical office LAN (old class C)
/25255.255.255.1280.0.0.1271281261/2 of a /24Smaller LAN or VLAN
/26255.255.255.1920.0.0.6364621/4 of a /24Smaller LAN or VLAN
/27255.255.255.2240.0.0.3132301/8 of a /24Small VLAN, phones, cameras
/28255.255.255.2400.0.0.1516141/16 of a /24Small VLAN, phones, cameras
/29255.255.255.2480.0.0.7861/32 of a /24Small fixed public block (5 usable)
/30255.255.255.2520.0.0.3421/64 of a /24Point-to-point (old style)
/31255.255.255.2540.0.0.1221/128 of a /24Point-to-point link (RFC 3021)
/32255.255.255.2550.0.0.0111/256 of a /24One host

IPv6 prefix reference

IPv6 prefix lengths
PrefixAddresses/64 LANs/48 sitesNibbleTypical use
/342,535,295,865,117,307,932,921,825,928,971,026,432 (2^125)2,305,843,009,213,693,95235,184,372,088,832NoAll global unicast (2000::/3)
/165,192,296,858,534,827,628,530,496,329,220,096 (2^112)281,474,976,710,6564,294,967,296Yes
/20324,518,553,658,426,726,783,156,020,576,256 (2^108)17,592,186,044,416268,435,456YesLarge provider allocation (RIPE minimum for some)
/29633,825,300,114,114,700,748,351,602,688 (2^99)34,359,738,368524,288NoRIPE allocation to a provider (often)
/3279,228,162,514,264,337,593,543,950,336 (2^96)4,294,967,29665,536YesProvider allocation (RIPE default)
/364,951,760,157,141,521,099,596,496,896 (2^92)268,435,4564,096Yes
/40309,485,009,821,345,068,724,781,056 (2^88)16,777,216256Yes
/4419,342,813,113,834,066,795,298,816 (2^84)1,048,57616Yes
/481,208,925,819,614,629,174,706,176 (2^80)65,5361YesOne site or organisation (RIPE PI / assignment)
/5275,557,863,725,914,323,419,136 (2^76)4,096Yes
/564,722,366,482,869,645,213,696 (2^72)256YesSmall site or home (common provider assignment)
/60295,147,905,179,352,825,856 (2^68)16YesSome home broadband (16 LANs)
/6418,446,744,073,709,551,616 (2^64)1YesOne LAN or VLAN (needed for SLAAC)
/7272,057,594,037,927,936 (2^56)1/256 of a /64Yes
/80281,474,976,710,656 (2^48)1/65,536 of a /64Yes
/964,294,967,2961/4,294,967,296 of a /64YesEmbeds an IPv4 address (NAT64)
/11265,5361/281,474,976,710,656 of a /64Yes
/1202561/72,057,594,037,927,936 of a /64Yes
/124161/1,152,921,504,606,846,976 of a /64Yes
/12641/4,611,686,018,427,387,904 of a /64No
/12721/9,223,372,036,854,775,808 of a /64NoPoint-to-point link (RFC 6164)
/12811/18,446,744,073,709,551,616 of a /64YesOne host or loopback

Private and special ranges

IPv4

Special-purpose ranges
RangeNameWhat it is
255.255.255.255/32Limited broadcastEvery host on the local network
0.0.0.0/8This networkNot routed; 0.0.0.0 means "any address" in settings
10.0.0.0/8Private (RFC 1918)Office and home networks; not routed on the internet
100.64.0.0/10Shared address space (CGNAT)Used by providers behind carrier-grade NAT (RFC 6598)
127.0.0.0/8LoopbackThis computer
169.254.0.0/16Link-local (APIPA)Self-assigned when no DHCP server answers
172.16.0.0/12Private (RFC 1918)Office and home networks; not routed on the internet
192.0.0.0/24IETF protocol assignmentsSpecial uses such as DS-Lite
192.0.2.0/24Documentation (TEST-NET-1)For examples; never used on a network
192.88.99.0/246to4 relay (deprecated)Formerly anycast for 6to4
192.168.0.0/16Private (RFC 1918)Office and home networks; not routed on the internet
198.18.0.0/15BenchmarkingNetwork equipment testing (RFC 2544)
198.51.100.0/24Documentation (TEST-NET-2)For examples; never used on a network
203.0.113.0/24Documentation (TEST-NET-3)For examples; never used on a network
224.0.0.0/4MulticastOne-to-many traffic, such as IPTV and routing protocols
240.0.0.0/4ReservedFuture use; not usable on most systems

IPv6

Special-purpose ranges
RangeNameWhat it is
::/128UnspecifiedNo address; :: means "any address" in settings
::1/128LoopbackThis computer
::ffff:0:0/96IPv4-mappedAn IPv4 address written as IPv6
64:ff9b::/96NAT64IPv4 addresses reached through a NAT64 gateway
100::/64Discard onlyTraffic sent here is dropped (RFC 6666)
2001:db8::/32DocumentationFor examples; never used on a network
2001::/32TeredoIPv6 tunnelled over IPv4 UDP
2002::/166to4IPv6 tunnelled over IPv4 (largely retired)
3fff::/20DocumentationFor examples (RFC 9637)
fc00::/7Unique local (ULA)Private IPv6, like RFC 1918; usually fd00::/8
fe80::/10Link-localEvery IPv6 interface has one; not routed
ff00::/8MulticastOne-to-many traffic; replaces broadcast
2000::/3Global unicastPublic 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.