# IP Subnet Calculator
This module calculates optimal subnet masks for non-standard IP ranges, e.g. `5.4.3.21 - 6.7.8.9`

[View demo](http://salieri.github.io/IPSubnetCalculator/)


## What does it do?
* Calculates subnet masks for standard and non-standard IP ranges. For example, `10.0.0.5 - 10.0.0.23` will result in `10.0.0.5/32, 10.0.0.6/31, 10.0.0.8/29, 10.0.0.16/29`.
* Calculates CIDR prefixes from subnet masks, e.g. `10.0.0.5/255.255.128.0` will result in `10.0.0.0/17`.
* Calculates subnet masks from CIDR prefixes, e.g. `10.0.0.5/17` will result in `255.255.128.0`.


## Support
* Node.js
* Direct browser use


## Installation
```sh
> npm install ip-subnet-calculator
```


## Node.js
```javascript
import * as IPSubnetCalculator from 'ip-subnet-calculator';
// or: const IPSubnetCalculator = require('ip-subnet-calculator');

console.log(IpSubnetCalculator.isIp('127.0.0.1')); // true
console.log(IpSubnetCalculator.toDecimal('127.0.0.1')); // 2130706433

console.log(IpSubnetCalculator.calculate('5.4.3.21', '6.7.8.9'));
```

## Direct browser use
```html
<script src='lib/ip-subnet-calculator.browser.js'></script>

<script>
    console.log(isIp( 127.0.0.1')); // true
    console.log(toDecimal('127.0.0.1')); // 2130706433
    
    console.log(calculate( '5.4.3.21', '6.7.8.9' ));
</script>
```


## API

### IpSubnetCalculator.calculate(ipStart, ipEnd)
Calculates an optimal set of IP masks for the given IP address range.

> *ipStart* (`string|number`) Lowest IP in the range to be calculated in string (`123.123.123.0`) or numeric (`2071689984`) format.
> 
> *ipEnd* (`string|number`) Highest IP (inclusive) in the range to be calculated in string (`123.123.123.255`) or numeric (`2071690239`) format.

The function returns `null` in case of an error. Otherwise, an array containing one or more subnet
masks is returned:

```javascript
const result = [
  {
    ipLow              : 2071689984,
    ipLowStr           : "123.123.123.0",
    ipHigh             : 2071690239,
    ipHighStr          : "123.123.123.255",
    prefixMask         : 4294967040,
    prefixMaskStr      : "255.255.255.0",
    prefixSize         : 24,
    invertedMask       : 255,
    invertedMaskStr    : "0.0.0.255",
    invertedMaskSize   : 8
  },
  
  ...
];
```

Each object in question contain the following properties:

| Property          | Use                                                            |
:------------------|:---------------------------------------------------------------|
| `ipLow`           | Decimal representation of the lowest IP address in the range   |
| `ipLowStr`        | String representation of the lowest IP address in the range    |
| `ipHigh`          | Decimal representation of the highest IP address in the range  |
| `ipHighStr`       | String representation of the highest IP address in the range   |
| `prefixMask`      | Decimal representation of the prefix (subnet) mask             |
| `prefixMaskStr`   | String representation of the prefix (subnet) mask              |
| `prefixSize`      | Size of the prefix (subnet) mask in bits                       |
| `invertedMask`    | Decimal representation of the inverted prefix mask             |
| `invertedMaskStr` | String representation of the inverted prefix mask              |
| `invertedSize`    | Size of the inverted prefix max in bits                        |

### IpSubnetCalculator.calculateSubnetMask(ip, prefixSize)
Calculates a subnet mask from CIDR prefix.

> *ip* (`string|number`) IP address in string or numeric format
> 
> *prefixSize* (`number`) Number of relevant bits in the subnet mask

The function returns an object containing full description of the IP range, as described in `IpSubnetCalculator.calculate()`.

### IpSubnetCalculator.calculateCIDRPrefix(ip, subnetMask)
Calculates a CIDR prefix from subnet mask.

> *ip* (`string|number`) IP address in string or numeric format
>
> *subnetMask* (`string|number`) IP subnet mask in string or numeric format

The function returns an object containing full description of the IP range, as described in `IpSubnetCalculator.calculate()`.


## Test Functions

### IpSubnetCalculator.isIp(ipStr)
Tests whether string is an IP address.

> *ipStr* (`string`) A string

The function returns a `true` if the string is an IP address, `false` otherwise.

### IpSubnetCalculator.isDecimalIp(ipNum)
Tests whether `ipNum` is a decimal IP address.

> *ipNum* (`number`) A number

The function returns a `true` if the number is an IP address, `false` otherwise.


## Conversion Functions

### IpSubnetCalculator.toDecimal(ip)
Calculates a decimal integer from an string IP address.

> *ip* (`string|number`) IP address in string format

The function returns a decimal representation of an IP address as an integer. If a valid numeric representation 
of an IP is passed to this function, it is returned unmodified.

If an invalid value is passed to the function, it will `throw` an `Error` object.


### IpSubnetCalculator.toString(num)
> *num* (`number|string`) Decimal representation of an IP address.

The function returns an IP address as a string. If a valid string representation of an IP is passed to this function,
it is returned unmodified.

If an invalid value is passed to the function, it will `throw` an `Error` object.


## License
[MIT](http://opensource.org/licenses/MIT)