A DHCP server written in JavaScript
npm install @u4/dhcp
node-dhcp is a RFC compliant DHCP client and server implementation on top of node.js.
Motivation
===
A DHCP server can be used to configure the entire local network. Typical parameters that can be organized with a DHCP server are ip-addresses, gateways / router, DNS server and really a lot more. DHCP is quite old and well establishd solutions are on the market, commercially and open source - so why a new implementation?
I was searching for a minimalistic DHCP server, which is robust and highly configurable. The first problem I had was: I wanted to deliver an IP address to a Raspberry PI without static configuration right out of my Macbook. However, Apple made it almost impossible to configure the onboard DHCP-server with newer versions of OSX.
The second motivation was this. In times of home automation and IoT, I was thinking of a solution, which can trigger something when I come home. DHCP is a good idea here, since any device will broadcast to the network, as soon as it connects. So why not playing the imperial march when you come back home?
Another problem I had was, I wanted to query DHCP servers without actually change the local configuration.
These problems were the trigger to start reading the RFC's and the protocol is really not that complicated. As such, this project was born.
Remark: By nature, network services are quite complex, so please test, test, test!
Usage
===
Command line
---
When installed globally, node-dhcp provides two executables, a client dhcp and a server dhcpd. The client simply retrieves network configuration from a DHCP server and prints the configuration after a complete handshake. All additional (defined in lib/options.js) fields can be specified as list of arguments:
``bashsudo dhcp hostname [--mac 12:23:34:45:56:67]
output:
netmask : 255.255.255.0
router : 192.168.1.1
dns : 8.8.8.8, 8.8.4.4
server : 192.168.1.1
hostname : web392
`
On the other hand, the server can be used to provide the data:
`bash`
sudo dhcpd --range 192.168.1.2-192.168.1.99 --hostname web392 --server 192.168.1.1 --router 192.168.1.1
All available options can be found in lib/options.js. The more powerful interface however, is the JavaScript API.
Simple DHCP Server
---
`js
var dhcp = require('dhcp');
var s = dhcpd.createServer({
// System settings
range: [
"192.168.3.10", "192.168.3.99"
],
forceOptions: ['hostname'], // Options that need to be sent, even if they were not requested
randomIP: true, // Get random new IP from pool instead of keeping one ip
static: {
"11:22:33:44:55:66": "192.168.3.100"
},
// Option settings (there are MUCH more)
netmask: '255.255.255.0',
router: [
'192.168.0.1'
],
dns: ["8.8.8.8", "8.8.4.4"],
hostname: "kacknup",
broadcast: '192.168.0.255',
server: '192.168.0.1', // This is us
bootFile: function (req, res) {
// res.ip - the actual ip allocated for the client
if (req.clientId === 'foo bar') {
return 'x86linux.0';
} else {
return 'x64linux.0';
}
}
});
s.listen();
`
Any config directive can be a function, like illustrated with the bootFile directive for PXE boot. This way you get a fully programable DHCP server.
Simple DHCP Client
---
`js
var dhcp = require('dhcp');
var s = dhcp.createClient();
s.on('bound', function (state) {
console.log("State: ", state);
// Configure your host system, based on the current state:
// ip address add IP/MASK dev eth0
//
//
//
});
s.listen();
s.sendDiscover();
`
Sniff DHCP Traffic
---
For research purposes it's also possible to just get triggered when broadcast events occur. This way an own DHCP server can be implemented. It's also possible to just listen to the traffic on the network, without answering. This can be used to automate something when a device enters the network (you come back home from work and your mobile phone gets into wifi) or to spot malicious DHCP servers on the network:
`js
var dhcp = require('dhcp');
var s = dhcp.createBroadcastHandler();
s.on('message', function (data) {
if (data.options[53] === dhcp.DHCPDISCOVER) {
if (data.chaddr === '12-34-56-78-90-AB') {
console.log('Welcome home!');
}
}
});
s.listen();
`
Docker
===
Quick test
---
`bash`Build the image
docker build -t infusion/node-dhcp:0 .Start the server
docker run -d --name dhcpd infusion/node-dhcp:0Start a client in the container (and send process to background)
docker exec dhcpd dhcp hostname --mac 12:23:34:45:56:67 &Show the server logs
docker logs dhcpd
Configuration assuming Host broadcast
---
Assuming the dhcp server is on a broadcast network:
`bash`Build the image
docker build -t infusion/node-dhcp:0 .Start the server
docker run --net=host -d --name dhcpd infusion/node-dhcp:0
Configuration assuming router DHCP relay
---
Assuming a router is relaying DHCP to multiple IP addresses on server host:
`bash`Build the image
docker build -t infusion/node-dhcp:0 .Start the servers
docker run -p the.host.ip:67:67/udp -d --name dhcpd1 infusion/node-dhcp:0
docker run -p other.host.ip:67:67/udp -d --name dhcpd2 infusion/node-dhcp:0
Installation
===
Installing node-dhcp is as easy as cloning this repo or use npmjs:
`bash`
npm install dhcp
If command line tools dhcp and dhcpd shall be installed, npmjs can be used as well:
`bash`
npm install dhcp -g
Configuration
===
Besides options listed in the lib/options.js file (with the config key), a few global options can be used:
- range: Two element array, representing the IP range the server operates onforceOptions
- : Array of options that are forced to be sentstatic
- : A static IP binding object of the form mac -> ip
Not yet implemented features
===
node-dhcp does not set timers already on the client to periodically send RENEW or REBIND messages. If you need this feature, please file a bug ticket.
Troubleshooting
===
EACCESS Error
---
Since the programs need to bind to port 67 and 68, root privileges are required. If you want to use dhcp and dhcpd without root privileges, change the port to something above 1024.
No data is received
---
A broadcast is typically not spread across all interfaces. In order to route the broadcast to a specific interface, you can reroute 255.255.255.255.
Linux
---
`bash`
route add -host 255.255.255.255 dev eth0
OS-X
---
`bash`
sudo route add -host 255.255.255.255 -interface en4
DHCP Options
---
A wide range of options are already implemented. Custom options can be defined with
`js`
const dhcpd = require("dhcp")
dhcpd.addOption(123, {
config: "testConfig",
type: "ASCII",
name: "Test Option"
});
Testing
===
If you plan to enhance the library, make sure you add test cases and all the previous tests are passing. You can test the library with
`bash``
npm test
Copyright and licensing
===
Copyright (c) 2017, Robert Eisele
Dual licensed under the MIT or GPL Version 2 licenses.