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.

Network6.64.0.0/10
Usable hosts4,194,302
Subnet mask255.192.0.0
Addresses4,194,304
Network address
6.64.0.0
Broadcast address
6.127.255.255
First usable
6.64.0.1
Last usable
6.127.255.254
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 06400000 · Integer 104857600 to 109051903
Reverse DNS zones
64.6.in-addr.arpa
65.6.in-addr.arpa
66.6.in-addr.arpa
67.6.in-addr.arpa
68.6.in-addr.arpa
69.6.in-addr.arpa
70.6.in-addr.arpa
71.6.in-addr.arpa
72.6.in-addr.arpa
73.6.in-addr.arpa
74.6.in-addr.arpa
75.6.in-addr.arpa
76.6.in-addr.arpa
77.6.in-addr.arpa
78.6.in-addr.arpa
79.6.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
Address00000110.01000000.00000000.000000006.64.0.0
Subnet mask11111111.11000000.00000000.00000000255.192.0.0
Network00000110.01000000.00000000.000000006.64.0.0
Broadcast00000110.01111111.11111111.111111116.127.255.255
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)

6.64.0.0/10 makes 128 subnets of /17.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
16.64.0.0/176.64.0.1 to 6.64.127.2546.64.127.25532,766
26.64.128.0/176.64.128.1 to 6.64.255.2546.64.255.25532,766
36.65.0.0/176.65.0.1 to 6.65.127.2546.65.127.25532,766
46.65.128.0/176.65.128.1 to 6.65.255.2546.65.255.25532,766
56.66.0.0/176.66.0.1 to 6.66.127.2546.66.127.25532,766
66.66.128.0/176.66.128.1 to 6.66.255.2546.66.255.25532,766
76.67.0.0/176.67.0.1 to 6.67.127.2546.67.127.25532,766
86.67.128.0/176.67.128.1 to 6.67.255.2546.67.255.25532,766
96.68.0.0/176.68.0.1 to 6.68.127.2546.68.127.25532,766
106.68.128.0/176.68.128.1 to 6.68.255.2546.68.255.25532,766
116.69.0.0/176.69.0.1 to 6.69.127.2546.69.127.25532,766
126.69.128.0/176.69.128.1 to 6.69.255.2546.69.255.25532,766
136.70.0.0/176.70.0.1 to 6.70.127.2546.70.127.25532,766
146.70.128.0/176.70.128.1 to 6.70.255.2546.70.255.25532,766
156.71.0.0/176.71.0.1 to 6.71.127.2546.71.127.25532,766
166.71.128.0/176.71.128.1 to 6.71.255.2546.71.255.25532,766
176.72.0.0/176.72.0.1 to 6.72.127.2546.72.127.25532,766
186.72.128.0/176.72.128.1 to 6.72.255.2546.72.255.25532,766
196.73.0.0/176.73.0.1 to 6.73.127.2546.73.127.25532,766
206.73.128.0/176.73.128.1 to 6.73.255.2546.73.255.25532,766
216.74.0.0/176.74.0.1 to 6.74.127.2546.74.127.25532,766
226.74.128.0/176.74.128.1 to 6.74.255.2546.74.255.25532,766
236.75.0.0/176.75.0.1 to 6.75.127.2546.75.127.25532,766
246.75.128.0/176.75.128.1 to 6.75.255.2546.75.255.25532,766
256.76.0.0/176.76.0.1 to 6.76.127.2546.76.127.25532,766
266.76.128.0/176.76.128.1 to 6.76.255.2546.76.255.25532,766
276.77.0.0/176.77.0.1 to 6.77.127.2546.77.127.25532,766
286.77.128.0/176.77.128.1 to 6.77.255.2546.77.255.25532,766
296.78.0.0/176.78.0.1 to 6.78.127.2546.78.127.25532,766
306.78.128.0/176.78.128.1 to 6.78.255.2546.78.255.25532,766
316.79.0.0/176.79.0.1 to 6.79.127.2546.79.127.25532,766
326.79.128.0/176.79.128.1 to 6.79.255.2546.79.255.25532,766
336.80.0.0/176.80.0.1 to 6.80.127.2546.80.127.25532,766
346.80.128.0/176.80.128.1 to 6.80.255.2546.80.255.25532,766
356.81.0.0/176.81.0.1 to 6.81.127.2546.81.127.25532,766
366.81.128.0/176.81.128.1 to 6.81.255.2546.81.255.25532,766
376.82.0.0/176.82.0.1 to 6.82.127.2546.82.127.25532,766
386.82.128.0/176.82.128.1 to 6.82.255.2546.82.255.25532,766
396.83.0.0/176.83.0.1 to 6.83.127.2546.83.127.25532,766
406.83.128.0/176.83.128.1 to 6.83.255.2546.83.255.25532,766
416.84.0.0/176.84.0.1 to 6.84.127.2546.84.127.25532,766
426.84.128.0/176.84.128.1 to 6.84.255.2546.84.255.25532,766
436.85.0.0/176.85.0.1 to 6.85.127.2546.85.127.25532,766
446.85.128.0/176.85.128.1 to 6.85.255.2546.85.255.25532,766
456.86.0.0/176.86.0.1 to 6.86.127.2546.86.127.25532,766
466.86.128.0/176.86.128.1 to 6.86.255.2546.86.255.25532,766
476.87.0.0/176.87.0.1 to 6.87.127.2546.87.127.25532,766
486.87.128.0/176.87.128.1 to 6.87.255.2546.87.255.25532,766
496.88.0.0/176.88.0.1 to 6.88.127.2546.88.127.25532,766
506.88.128.0/176.88.128.1 to 6.88.255.2546.88.255.25532,766
516.89.0.0/176.89.0.1 to 6.89.127.2546.89.127.25532,766
526.89.128.0/176.89.128.1 to 6.89.255.2546.89.255.25532,766
536.90.0.0/176.90.0.1 to 6.90.127.2546.90.127.25532,766
546.90.128.0/176.90.128.1 to 6.90.255.2546.90.255.25532,766
556.91.0.0/176.91.0.1 to 6.91.127.2546.91.127.25532,766
566.91.128.0/176.91.128.1 to 6.91.255.2546.91.255.25532,766
576.92.0.0/176.92.0.1 to 6.92.127.2546.92.127.25532,766
586.92.128.0/176.92.128.1 to 6.92.255.2546.92.255.25532,766
596.93.0.0/176.93.0.1 to 6.93.127.2546.93.127.25532,766
606.93.128.0/176.93.128.1 to 6.93.255.2546.93.255.25532,766
616.94.0.0/176.94.0.1 to 6.94.127.2546.94.127.25532,766
626.94.128.0/176.94.128.1 to 6.94.255.2546.94.255.25532,766
636.95.0.0/176.95.0.1 to 6.95.127.2546.95.127.25532,766
646.95.128.0/176.95.128.1 to 6.95.255.2546.95.255.25532,766
656.96.0.0/176.96.0.1 to 6.96.127.2546.96.127.25532,766
666.96.128.0/176.96.128.1 to 6.96.255.2546.96.255.25532,766
676.97.0.0/176.97.0.1 to 6.97.127.2546.97.127.25532,766
686.97.128.0/176.97.128.1 to 6.97.255.2546.97.255.25532,766
696.98.0.0/176.98.0.1 to 6.98.127.2546.98.127.25532,766
706.98.128.0/176.98.128.1 to 6.98.255.2546.98.255.25532,766
716.99.0.0/176.99.0.1 to 6.99.127.2546.99.127.25532,766
726.99.128.0/176.99.128.1 to 6.99.255.2546.99.255.25532,766
736.100.0.0/176.100.0.1 to 6.100.127.2546.100.127.25532,766
746.100.128.0/176.100.128.1 to 6.100.255.2546.100.255.25532,766
756.101.0.0/176.101.0.1 to 6.101.127.2546.101.127.25532,766
766.101.128.0/176.101.128.1 to 6.101.255.2546.101.255.25532,766
776.102.0.0/176.102.0.1 to 6.102.127.2546.102.127.25532,766
786.102.128.0/176.102.128.1 to 6.102.255.2546.102.255.25532,766
796.103.0.0/176.103.0.1 to 6.103.127.2546.103.127.25532,766
806.103.128.0/176.103.128.1 to 6.103.255.2546.103.255.25532,766
816.104.0.0/176.104.0.1 to 6.104.127.2546.104.127.25532,766
826.104.128.0/176.104.128.1 to 6.104.255.2546.104.255.25532,766
836.105.0.0/176.105.0.1 to 6.105.127.2546.105.127.25532,766
846.105.128.0/176.105.128.1 to 6.105.255.2546.105.255.25532,766
856.106.0.0/176.106.0.1 to 6.106.127.2546.106.127.25532,766
866.106.128.0/176.106.128.1 to 6.106.255.2546.106.255.25532,766
876.107.0.0/176.107.0.1 to 6.107.127.2546.107.127.25532,766
886.107.128.0/176.107.128.1 to 6.107.255.2546.107.255.25532,766
896.108.0.0/176.108.0.1 to 6.108.127.2546.108.127.25532,766
906.108.128.0/176.108.128.1 to 6.108.255.2546.108.255.25532,766
916.109.0.0/176.109.0.1 to 6.109.127.2546.109.127.25532,766
926.109.128.0/176.109.128.1 to 6.109.255.2546.109.255.25532,766
936.110.0.0/176.110.0.1 to 6.110.127.2546.110.127.25532,766
946.110.128.0/176.110.128.1 to 6.110.255.2546.110.255.25532,766
956.111.0.0/176.111.0.1 to 6.111.127.2546.111.127.25532,766
966.111.128.0/176.111.128.1 to 6.111.255.2546.111.255.25532,766
976.112.0.0/176.112.0.1 to 6.112.127.2546.112.127.25532,766
986.112.128.0/176.112.128.1 to 6.112.255.2546.112.255.25532,766
996.113.0.0/176.113.0.1 to 6.113.127.2546.113.127.25532,766
1006.113.128.0/176.113.128.1 to 6.113.255.2546.113.255.25532,766
1016.114.0.0/176.114.0.1 to 6.114.127.2546.114.127.25532,766
1026.114.128.0/176.114.128.1 to 6.114.255.2546.114.255.25532,766
1036.115.0.0/176.115.0.1 to 6.115.127.2546.115.127.25532,766
1046.115.128.0/176.115.128.1 to 6.115.255.2546.115.255.25532,766
1056.116.0.0/176.116.0.1 to 6.116.127.2546.116.127.25532,766
1066.116.128.0/176.116.128.1 to 6.116.255.2546.116.255.25532,766
1076.117.0.0/176.117.0.1 to 6.117.127.2546.117.127.25532,766
1086.117.128.0/176.117.128.1 to 6.117.255.2546.117.255.25532,766
1096.118.0.0/176.118.0.1 to 6.118.127.2546.118.127.25532,766
1106.118.128.0/176.118.128.1 to 6.118.255.2546.118.255.25532,766
1116.119.0.0/176.119.0.1 to 6.119.127.2546.119.127.25532,766
1126.119.128.0/176.119.128.1 to 6.119.255.2546.119.255.25532,766
1136.120.0.0/176.120.0.1 to 6.120.127.2546.120.127.25532,766
1146.120.128.0/176.120.128.1 to 6.120.255.2546.120.255.25532,766
1156.121.0.0/176.121.0.1 to 6.121.127.2546.121.127.25532,766
1166.121.128.0/176.121.128.1 to 6.121.255.2546.121.255.25532,766
1176.122.0.0/176.122.0.1 to 6.122.127.2546.122.127.25532,766
1186.122.128.0/176.122.128.1 to 6.122.255.2546.122.255.25532,766
1196.123.0.0/176.123.0.1 to 6.123.127.2546.123.127.25532,766
1206.123.128.0/176.123.128.1 to 6.123.255.2546.123.255.25532,766
1216.124.0.0/176.124.0.1 to 6.124.127.2546.124.127.25532,766
1226.124.128.0/176.124.128.1 to 6.124.255.2546.124.255.25532,766
1236.125.0.0/176.125.0.1 to 6.125.127.2546.125.127.25532,766
1246.125.128.0/176.125.128.1 to 6.125.255.2546.125.255.25532,766
1256.126.0.0/176.126.0.1 to 6.126.127.2546.126.127.25532,766
1266.126.128.0/176.126.128.1 to 6.126.255.2546.126.255.25532,766
1276.127.0.0/176.127.0.1 to 6.127.127.2546.127.127.25532,766
1286.127.128.0/176.127.128.1 to 6.127.255.2546.127.255.25532,766

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.