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.

Network41.192.0.0/10
Usable hosts4,194,302
Subnet mask255.192.0.0
Addresses4,194,304
Network address
41.192.0.0
Broadcast address
41.255.255.255
First usable
41.192.0.1
Last usable
41.255.255.254
Usable hosts
4,194,302 (4,194,304 less the network and broadcast addresses)
Subnet mask
255.192.0.0
Wildcard mask
0.63.255.255 (Cisco ACLs, OSPF)
Prefix length
/10
Type
Public public
Old class
A (default /8)
As numbers
Hex 29C00000 · Integer 700448768 to 704643071
Reverse DNS zones
192.41.in-addr.arpa
193.41.in-addr.arpa
194.41.in-addr.arpa
195.41.in-addr.arpa
196.41.in-addr.arpa
197.41.in-addr.arpa
198.41.in-addr.arpa
199.41.in-addr.arpa
200.41.in-addr.arpa
201.41.in-addr.arpa
202.41.in-addr.arpa
203.41.in-addr.arpa
204.41.in-addr.arpa
205.41.in-addr.arpa
206.41.in-addr.arpa
207.41.in-addr.arpa
and 48 more
/10 is not on a 8-bit boundary, so it takes 64 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00101001.11000000.00000000.0000000041.192.0.0
Subnet mask11111111.11000000.00000000.00000000255.192.0.0
Network00101001.11000000.00000000.0000000041.192.0.0
Broadcast00101001.11111111.11111111.1111111141.255.255.255
Split into smaller subnets/17
/11 (2)/12 (4)/13 (8)/14 (16)/15 (32)/16 (64)/17 (128)/18 (256)/19 (512)/20 (1,024)/21 (2,048)/22 (4,096)

41.192.0.0/10 makes 128 subnets of /17.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
141.192.0.0/1741.192.0.1 to 41.192.127.25441.192.127.25532,766
241.192.128.0/1741.192.128.1 to 41.192.255.25441.192.255.25532,766
341.193.0.0/1741.193.0.1 to 41.193.127.25441.193.127.25532,766
441.193.128.0/1741.193.128.1 to 41.193.255.25441.193.255.25532,766
541.194.0.0/1741.194.0.1 to 41.194.127.25441.194.127.25532,766
641.194.128.0/1741.194.128.1 to 41.194.255.25441.194.255.25532,766
741.195.0.0/1741.195.0.1 to 41.195.127.25441.195.127.25532,766
841.195.128.0/1741.195.128.1 to 41.195.255.25441.195.255.25532,766
941.196.0.0/1741.196.0.1 to 41.196.127.25441.196.127.25532,766
1041.196.128.0/1741.196.128.1 to 41.196.255.25441.196.255.25532,766
1141.197.0.0/1741.197.0.1 to 41.197.127.25441.197.127.25532,766
1241.197.128.0/1741.197.128.1 to 41.197.255.25441.197.255.25532,766
1341.198.0.0/1741.198.0.1 to 41.198.127.25441.198.127.25532,766
1441.198.128.0/1741.198.128.1 to 41.198.255.25441.198.255.25532,766
1541.199.0.0/1741.199.0.1 to 41.199.127.25441.199.127.25532,766
1641.199.128.0/1741.199.128.1 to 41.199.255.25441.199.255.25532,766
1741.200.0.0/1741.200.0.1 to 41.200.127.25441.200.127.25532,766
1841.200.128.0/1741.200.128.1 to 41.200.255.25441.200.255.25532,766
1941.201.0.0/1741.201.0.1 to 41.201.127.25441.201.127.25532,766
2041.201.128.0/1741.201.128.1 to 41.201.255.25441.201.255.25532,766
2141.202.0.0/1741.202.0.1 to 41.202.127.25441.202.127.25532,766
2241.202.128.0/1741.202.128.1 to 41.202.255.25441.202.255.25532,766
2341.203.0.0/1741.203.0.1 to 41.203.127.25441.203.127.25532,766
2441.203.128.0/1741.203.128.1 to 41.203.255.25441.203.255.25532,766
2541.204.0.0/1741.204.0.1 to 41.204.127.25441.204.127.25532,766
2641.204.128.0/1741.204.128.1 to 41.204.255.25441.204.255.25532,766
2741.205.0.0/1741.205.0.1 to 41.205.127.25441.205.127.25532,766
2841.205.128.0/1741.205.128.1 to 41.205.255.25441.205.255.25532,766
2941.206.0.0/1741.206.0.1 to 41.206.127.25441.206.127.25532,766
3041.206.128.0/1741.206.128.1 to 41.206.255.25441.206.255.25532,766
3141.207.0.0/1741.207.0.1 to 41.207.127.25441.207.127.25532,766
3241.207.128.0/1741.207.128.1 to 41.207.255.25441.207.255.25532,766
3341.208.0.0/1741.208.0.1 to 41.208.127.25441.208.127.25532,766
3441.208.128.0/1741.208.128.1 to 41.208.255.25441.208.255.25532,766
3541.209.0.0/1741.209.0.1 to 41.209.127.25441.209.127.25532,766
3641.209.128.0/1741.209.128.1 to 41.209.255.25441.209.255.25532,766
3741.210.0.0/1741.210.0.1 to 41.210.127.25441.210.127.25532,766
3841.210.128.0/1741.210.128.1 to 41.210.255.25441.210.255.25532,766
3941.211.0.0/1741.211.0.1 to 41.211.127.25441.211.127.25532,766
4041.211.128.0/1741.211.128.1 to 41.211.255.25441.211.255.25532,766
4141.212.0.0/1741.212.0.1 to 41.212.127.25441.212.127.25532,766
4241.212.128.0/1741.212.128.1 to 41.212.255.25441.212.255.25532,766
4341.213.0.0/1741.213.0.1 to 41.213.127.25441.213.127.25532,766
4441.213.128.0/1741.213.128.1 to 41.213.255.25441.213.255.25532,766
4541.214.0.0/1741.214.0.1 to 41.214.127.25441.214.127.25532,766
4641.214.128.0/1741.214.128.1 to 41.214.255.25441.214.255.25532,766
4741.215.0.0/1741.215.0.1 to 41.215.127.25441.215.127.25532,766
4841.215.128.0/1741.215.128.1 to 41.215.255.25441.215.255.25532,766
4941.216.0.0/1741.216.0.1 to 41.216.127.25441.216.127.25532,766
5041.216.128.0/1741.216.128.1 to 41.216.255.25441.216.255.25532,766
5141.217.0.0/1741.217.0.1 to 41.217.127.25441.217.127.25532,766
5241.217.128.0/1741.217.128.1 to 41.217.255.25441.217.255.25532,766
5341.218.0.0/1741.218.0.1 to 41.218.127.25441.218.127.25532,766
5441.218.128.0/1741.218.128.1 to 41.218.255.25441.218.255.25532,766
5541.219.0.0/1741.219.0.1 to 41.219.127.25441.219.127.25532,766
5641.219.128.0/1741.219.128.1 to 41.219.255.25441.219.255.25532,766
5741.220.0.0/1741.220.0.1 to 41.220.127.25441.220.127.25532,766
5841.220.128.0/1741.220.128.1 to 41.220.255.25441.220.255.25532,766
5941.221.0.0/1741.221.0.1 to 41.221.127.25441.221.127.25532,766
6041.221.128.0/1741.221.128.1 to 41.221.255.25441.221.255.25532,766
6141.222.0.0/1741.222.0.1 to 41.222.127.25441.222.127.25532,766
6241.222.128.0/1741.222.128.1 to 41.222.255.25441.222.255.25532,766
6341.223.0.0/1741.223.0.1 to 41.223.127.25441.223.127.25532,766
6441.223.128.0/1741.223.128.1 to 41.223.255.25441.223.255.25532,766
6541.224.0.0/1741.224.0.1 to 41.224.127.25441.224.127.25532,766
6641.224.128.0/1741.224.128.1 to 41.224.255.25441.224.255.25532,766
6741.225.0.0/1741.225.0.1 to 41.225.127.25441.225.127.25532,766
6841.225.128.0/1741.225.128.1 to 41.225.255.25441.225.255.25532,766
6941.226.0.0/1741.226.0.1 to 41.226.127.25441.226.127.25532,766
7041.226.128.0/1741.226.128.1 to 41.226.255.25441.226.255.25532,766
7141.227.0.0/1741.227.0.1 to 41.227.127.25441.227.127.25532,766
7241.227.128.0/1741.227.128.1 to 41.227.255.25441.227.255.25532,766
7341.228.0.0/1741.228.0.1 to 41.228.127.25441.228.127.25532,766
7441.228.128.0/1741.228.128.1 to 41.228.255.25441.228.255.25532,766
7541.229.0.0/1741.229.0.1 to 41.229.127.25441.229.127.25532,766
7641.229.128.0/1741.229.128.1 to 41.229.255.25441.229.255.25532,766
7741.230.0.0/1741.230.0.1 to 41.230.127.25441.230.127.25532,766
7841.230.128.0/1741.230.128.1 to 41.230.255.25441.230.255.25532,766
7941.231.0.0/1741.231.0.1 to 41.231.127.25441.231.127.25532,766
8041.231.128.0/1741.231.128.1 to 41.231.255.25441.231.255.25532,766
8141.232.0.0/1741.232.0.1 to 41.232.127.25441.232.127.25532,766
8241.232.128.0/1741.232.128.1 to 41.232.255.25441.232.255.25532,766
8341.233.0.0/1741.233.0.1 to 41.233.127.25441.233.127.25532,766
8441.233.128.0/1741.233.128.1 to 41.233.255.25441.233.255.25532,766
8541.234.0.0/1741.234.0.1 to 41.234.127.25441.234.127.25532,766
8641.234.128.0/1741.234.128.1 to 41.234.255.25441.234.255.25532,766
8741.235.0.0/1741.235.0.1 to 41.235.127.25441.235.127.25532,766
8841.235.128.0/1741.235.128.1 to 41.235.255.25441.235.255.25532,766
8941.236.0.0/1741.236.0.1 to 41.236.127.25441.236.127.25532,766
9041.236.128.0/1741.236.128.1 to 41.236.255.25441.236.255.25532,766
9141.237.0.0/1741.237.0.1 to 41.237.127.25441.237.127.25532,766
9241.237.128.0/1741.237.128.1 to 41.237.255.25441.237.255.25532,766
9341.238.0.0/1741.238.0.1 to 41.238.127.25441.238.127.25532,766
9441.238.128.0/1741.238.128.1 to 41.238.255.25441.238.255.25532,766
9541.239.0.0/1741.239.0.1 to 41.239.127.25441.239.127.25532,766
9641.239.128.0/1741.239.128.1 to 41.239.255.25441.239.255.25532,766
9741.240.0.0/1741.240.0.1 to 41.240.127.25441.240.127.25532,766
9841.240.128.0/1741.240.128.1 to 41.240.255.25441.240.255.25532,766
9941.241.0.0/1741.241.0.1 to 41.241.127.25441.241.127.25532,766
10041.241.128.0/1741.241.128.1 to 41.241.255.25441.241.255.25532,766
10141.242.0.0/1741.242.0.1 to 41.242.127.25441.242.127.25532,766
10241.242.128.0/1741.242.128.1 to 41.242.255.25441.242.255.25532,766
10341.243.0.0/1741.243.0.1 to 41.243.127.25441.243.127.25532,766
10441.243.128.0/1741.243.128.1 to 41.243.255.25441.243.255.25532,766
10541.244.0.0/1741.244.0.1 to 41.244.127.25441.244.127.25532,766
10641.244.128.0/1741.244.128.1 to 41.244.255.25441.244.255.25532,766
10741.245.0.0/1741.245.0.1 to 41.245.127.25441.245.127.25532,766
10841.245.128.0/1741.245.128.1 to 41.245.255.25441.245.255.25532,766
10941.246.0.0/1741.246.0.1 to 41.246.127.25441.246.127.25532,766
11041.246.128.0/1741.246.128.1 to 41.246.255.25441.246.255.25532,766
11141.247.0.0/1741.247.0.1 to 41.247.127.25441.247.127.25532,766
11241.247.128.0/1741.247.128.1 to 41.247.255.25441.247.255.25532,766
11341.248.0.0/1741.248.0.1 to 41.248.127.25441.248.127.25532,766
11441.248.128.0/1741.248.128.1 to 41.248.255.25441.248.255.25532,766
11541.249.0.0/1741.249.0.1 to 41.249.127.25441.249.127.25532,766
11641.249.128.0/1741.249.128.1 to 41.249.255.25441.249.255.25532,766
11741.250.0.0/1741.250.0.1 to 41.250.127.25441.250.127.25532,766
11841.250.128.0/1741.250.128.1 to 41.250.255.25441.250.255.25532,766
11941.251.0.0/1741.251.0.1 to 41.251.127.25441.251.127.25532,766
12041.251.128.0/1741.251.128.1 to 41.251.255.25441.251.255.25532,766
12141.252.0.0/1741.252.0.1 to 41.252.127.25441.252.127.25532,766
12241.252.128.0/1741.252.128.1 to 41.252.255.25441.252.255.25532,766
12341.253.0.0/1741.253.0.1 to 41.253.127.25441.253.127.25532,766
12441.253.128.0/1741.253.128.1 to 41.253.255.25441.253.255.25532,766
12541.254.0.0/1741.254.0.1 to 41.254.127.25441.254.127.25532,766
12641.254.128.0/1741.254.128.1 to 41.254.255.25441.254.255.25532,766
12741.255.0.0/1741.255.0.1 to 41.255.127.25441.255.127.25532,766
12841.255.128.0/1741.255.128.1 to 41.255.255.25441.255.255.25532,766

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.