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Tools
The Tools menu in the top bar holds two small network calculators. Each opens in a new tab, so it can sit beside the page you're working on. Any logged-in account can use them, read-only ones too; they don't read or change anything in LiteBlox.
Subnet Reference
A table of every IPv4 prefix from /0 to /32:
| Column | Shows |
|---|---|
| CIDR | the prefix length |
| Mask | the same as a dotted netmask, such as 255.255.255.0 for a /24 |
| Usable hosts | the addresses a host can have: all of them less the network and broadcast addresses |
| Next Net | where the next network of the same size starts |
The common sizes (/8, /16 and /24) are highlighted.
Next Net
Next Net is written over an address a.b.c.d on the network's boundary, adding to the octet that holds the prefix's last bit:
- a /24 steps the third octet by 1:
a.b.c+1.d, so after192.168.1.0/24comes192.168.2.0/24; - a /23 steps it by 2:
a.b.c+2.d; - a /26 steps the last octet by 64:
a.b.c.d+64, so after192.168.1.64/26comes192.168.1.128/26; - a /1 steps the first by 128:
a+128.b.c.d.
A /0 is every address, so it has no next network (n/a).
/31 and /32
A /31 has two usable addresses, not zero: on a point-to-point link there's no need for network and broadcast addresses, so both are used (RFC 3021). A /32 is a single host, such as a loopback or a route to one address.
Subnet Calculator
A visual calculator for splitting a network into smaller ones.
- Enter a network address and its prefix length, then Update. An address that isn't on the network's boundary is moved down to it, with a note saying so.
- Divide splits a row into two halves. The coloured badges on the right show every prefix a row belongs to; click a badge to join that network's rows back into one.
- Exclude subnets takes networks separated by commas (such as
192.168.1.128/25, 192.168.1.192/26). The calculator divides around them and shows them struck through in red; they can't be divided further. - Click the Range header to switch between the full range and the usable addresses.
- Bookmark or share this link keeps the whole layout (network, divisions and exclusions) in the address, so opening it again shows the same table.
- Reset joins everything back into the one network, after asking. Changing the prefix length of the base network asks first too, since it starts over.
- Copy Table copies the table as plain text, with the supernet and the excluded networks at the end. Browsers only let a page write to the clipboard over HTTPS (or on
localhost); over plain HTTP LiteBlox tries the older way, and if the browser refuses that too it shows the text in a box, selected, for you to copy.
Credit
The Subnet Calculator is an altered version of David C A Croft's Visual Subnet Calculator, Copyright (c) 2002, 2011, 2018, 2019 David C A Croft, modified for LiteBlox. It isn't the original software. Its license ships beside it as subnetcalc-LICENSE.txt.