rest2dhcp

A REST web service gateway to a DHCP server

The service acts as a REST web service for clients and as a DHCP relay to the DHCP server.
Therefore, it's possible to request IPs for more than one hostname or MAC address.

A REST web service gateway to a DHCP server

Usage:
  rest2dhcp [flags]
  rest2dhcp [command]

Available Commands:
  help        Help about any command
  version     Show the version info

Flags:
  -a, --access-log              Print access log messages (default true)
  -c, --client ip               Local IP for DHCP relay client
      --config string           Config file (default is $HOME/rest2dhcp.yaml)
  -S, --dhcp-server string      DHCP server name
  -d, --dhcp-timeout duration   DHCP query timeout (default 5s)
  -h, --help                    help for rest2dhcp
  -H, --hostname string         Hostname to listen on
  -k, --kubeconfig string       (optional) absolute path to the kubeconfig file (default "/home/dil/.kube/config")
  -m, --mode string             DHCP connection mode: udp, dual, fritzbox, packet, broken (default "auto")
  -n, --namespace string        Kubernetes namespace (default "default")
  -p, --port uint16             Port to listen on (default 8080)
  -q, --quiet                   Only access log messages
  -r, --relay ip                Relay IP for DHCP relay client
  -x, --retry duration          DHCP retry time (default 15s)
  -s, --server ip               DHCP server ip
  -K, --service string          Kubernetes service name
  -t, --timeout duration        Service query timeout (default 30s)
  -v, --verbose                 Verbose messages

Flags and Environment Variables

Parameter	Env Variable	Description	Default
client	CLIENT	IP of the local DHCP listener	IP to default gateway
server	SERVER	IP of the remote DHCP server	Default gateway
relay	RELAY	Published DHCP relay IP	Client IP
hostname	HOSTNAME	Hostname to listen on
port	PORT	Port of the web listener	8080
mode	MODE	Connection mode	auto
timeout	TIMEOUT	Web service timeout	30s
dhcp-timeout	DHCP_TIMEOUT	DHCP response timeout	5s
retry	RETRY	Wait time before retry	15s

Connection Mode

Unfortunately, the DHCP relay implementations are often very buggy or have some strange DoS protections. The gateway has four different implementations for the DHCP connection and an auto-detection.

Mode	Description	Test system
auto	A very simple auto-detection (only for development and testing)
udp	A UDP connection using port 67 for incoming and outgoing traffic	openwrt-19.07 ISC DHCP
dual	Like the UDP connection, but with a UDP packet connection for outgoing traffic	openwrt-19.07 ISC DHCP
fritzbox	A UDP packet connection sending DHCP packages with increasing src ports to port 67 and a UDP listener on port 67	Fritz!Box 7590
packet	A packet listener using port 67 for incoming and port 67 for outgoing traffic	openwrt-19.07 ISC DHCP
broken	A packet listener using port 68 for incoming and port 67 for outgoing traffic	Android 10 WiFi hotspot

Openwrt needs a very long time to respond on an IP request for an unknown host. It seems to be part of the DoS protection. Therefore, the timeout must be selected large enough.

A Fritzbox will not respond if the time between two DHCP relay requests with the same source port is less than 15 seconds. Therefore, the fritzbox connector increases the source port after each request.

The Android WiFi hotspot Android incorrectly sends responses to DHCP relay requests to port 68.

Docker usage

You can also use rest2dhcp as a docker-container.

SERVER=`IP of the DHCP server`
RELAY=`External IP of Docker host`

docker run -e SERVER=$SERVER -e RELAY=$RELAY -e MODE=udp -p 8080:8080 -p 67:67/udp  zauberhaus/rest2dhcp

You can use curl to test the server

curl http://localhost:8080/version

and should get a result like this

buildDate: 2020-08-20T23:08:04UTC
compiler: gc
gitCommit: 8af5609
gitTreeState: dirty
gitVersion: v0.9.22
goVersion: go1.14.7
platform: linux/amd64
dhcp: 192.168.1.1
relay: 192.168.1.4
mode: packet

API

The service provides an online documentation under the following url:

http://localhost:8080/api

Client

package main

import (
	"context"
	"fmt"

	"github.com/zauberhaus/rest2dhcp/client"
)

func main() {
	cl := client.NewClient("http://localhost:8080")

	version, err := cl.Version(context.Background())
	if err != nil {
		panic(err)
	}

	fmt.Println(version)

	lease, err := cl.Lease(context.Background(), "test", nil)
	if err != nil {
		panic(err)
	}

	fmt.Println(lease)

	lease, err = cl.Renew(context.Background(), lease.Hostname, lease.Mac, lease.IP)
	if err != nil {
		panic(err)
	}

	fmt.Println(lease)

	err = cl.Release(context.Background(), lease.Hostname, lease.Mac, lease.IP)
	if err != nil {
		panic(err)
	}
}

Build

Requirements:

• Linux
• Go 1.14

./build.sh

Docker build

Requirements:

• Docker

sudo ./scripts/build-docker.sh

The script creates a folder ./build with the executable