freebind.js

npm | github

inspired by freebind (the C project), this library takes advantage of the IP_FREEBIND socket option on Linux and allows you to bind sockets to random IP addresses from specified prefixes.

freebind.js is only supported on Linux -- it won't work on other platforms (since they don't have a FREEBIND socket option).

note that it is still very experimental, potential bug reports and pull requests are welcome.

setup

the setup is the same as you would expect from the original freebind project:

Assume your ISP has assigned the subnet 2a00:1450:4001:81b::/64 to your server. In order to make use of freebinding, you first need to configure the Linux AnyIP kernel feature in order to be able to bind a socket to an arbitrary IP address from this subnet as follows:

ip -6 route add local 2a00:1450:4001:81b::/64 dev lo

usage

freebind supports creating TCP sockets, and also provides a dispatcher wrapper for use with undici (aka native node >=18 fetch)

fetch

import { randomDispatcher } from 'freebind'

const dispatcher = randomDispatcher('fc00:dead:beef::/48')

const example1 = async () => console.log(
    await fetch(
        'https://icanhazip.com',
        { dispatcher }
    ).then(a => a.text())
)

// connections on IPs may be held open
// unless you explicitly close the connection
await example1(); // ~> fc00:dead:beef:4465:f5e0:26d4:2921:6891
await example1(); // ~> fc00:dead:beef:4465:f5e0:26d4:2921:6891
await example1(); // ~> fc00:dead:beef:4465:f5e0:26d4:2921:6891
await example1(); // ~> fc00:dead:beef:4465:f5e0:26d4:2921:6891

const example2 = async () => console.log(
    await fetch(
        'https://icanhazip.com',
        { dispatcher,
          headers: { connection: 'close' }
        }
    ).then(a => a.text())
)
await example2(); // ~> fc00:dead:beef:7d1e:b71e:1c77:1cc6:8a07
await example2(); // ~> fc00:dead:beef:31cd:a6e7:be0b:6872:b51a
await example2(); // ~> fc00:dead:beef:8f8e:c97f:2ba2:3a6:9d7b
await example2(); // ~> fc00:dead:beef:3a48:bb50:d193:471c:f553


/** If a hostname has no IPv6 (AAAA) record while you are trying to access
 ** it via IPv6 (or vice versa for IPv4 - although that would be pretty rare),
 ** freebind.js will throw an exception. This can be overridden by using { strict: false },
 ** which will make it fall back to regular fetch with IPv4. This is not the default
 ** because in many cases, this is not what you really want. **/
const dispatcher2 = randomDispatcher('fc00:dead:beef::/48')
const example3 = async () => console.log(
    await fetch(
        'https://ipinfo.io/json',
        { dispatcher,
          headers: { connection: 'close' }
        }
    ).then(a => a.text())
) // ~> Uncaught 'family mismatch for addr 34.117.59.81'

const dispatcher3 = randomDispatcher('fc00:dead:beef::/48', { strict: false })
const example4 = async () => console.log(
    await fetch(
        'https://ipinfo.io/json',
        { dispatcher,
          headers: { connection: 'close' }
        }
    ).then(a => a.text())
) // ~> {"ip":"127.0.0.1", "city": ...

tcp

import { tcp } from 'freebind'

// a random address will be bound to this socket
const sock = await tcp.createRandomSocket('::1', 9999, 'fc00:dead:beef::/48')
// returns a net.Socket: https://nodejs.org/api/net.html#class-netsocket

// you can also specify a specific address
const sock2 = await tcp.createSocket('hostname.com.example', 9999, 'fc00:dead:beef::b00b')

// you can also specify how many bits to
// randomize (the remainder is zeroed out)
const sock3 = await tcp.createRandomSocket('::1', 9999, 'fc00:dead:beef::/48', undefined, 8)
// (starting from most significant bits, e.g.
// the could be bound to IPs like:
// fc00:dead:beef:2c00::, fc00:dead:beef:3b00::
// fc00:dead:beef:f500::, and so on