DHCP Server

Multiple DHCP Servers can be run from a single machine. Each DHCP service is identified by a shared-network-name.

DHCP Server Example

In this example, we are offering address space in the 172.16.17.0/24 network, which is on eth1, and pppoe0 is our connection to the internet. We are using the network name dhcpexample.

Prerequisites

Configuring the PPPoE interface is assumed to be done already, and appears on pppoe0

Interface Configuration

set interface ethernet eth1 address 172.16.17.1/24

Multiple ranges can be defined and can contain holes.

set service dhcp-server shared-network-name dhcpexample authoritative
set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 default-router 172.16.17.1
set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 dns-server 172.16.17.1
set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 lease 86400
set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 range 0 start 172.16.17.100
set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 range 0 stop 172.16.17.199

Explanation

  • set service dhcp-server shared-network-name dhcpexample authoritative

    This says that this device is the only DHCP server for this network. If other devices are trying to offer DHCP leases, this machine will send ‘DHCPNAK’ to any device trying to request an IP address that is not valid for this network.

  • set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 default-router 172.16.17.1

    This is a configuration parameter for the subnet, saying that as part of the response, tell the client that I am the default router for this network

  • set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 dns-server 172.16.17.1

    This is a configuration parameter for the subnet, saying that as part of the response, tell the client that I am the DNS server for this network. If you do not want to run a DNS server, you could also provide one of the public DNS servers, such as google’s. You can add multiple entries by repeating the line.

  • set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 lease 86400

    Assign the IP address to this machine for 24 hours. It is unlikely you’d need to shorten this period, unless you are running a network with lots of devices appearing and disappearing.

  • set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 range 0 start 172.16.17.100

    Make a range of addresses available for clients starting from .100 […]

  • set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 range 0 stop 172.16.17.199

    […] and ending at .199

Failover

VyOS provides support for DHCP failover:

set service dhcp-server shared-network-name 'LAN' subnet '192.168.0.0/24' failover local-address '192.168.0.1'
set service dhcp-server shared-network-name 'LAN' subnet '192.168.0.0/24' failover name 'foo'
set service dhcp-server shared-network-name 'LAN' subnet '192.168.0.0/24' failover peer-address '192.168.0.2'

Note

name must be identical on both sides!

The primary and secondary statements determines whether the server is primary or secondary

set service dhcp-server shared-network-name 'LAN' subnet '192.168.0.0/24' failover status 'primary'

or

set service dhcp-server shared-network-name 'LAN' subnet '192.168.0.0/24' failover status 'secondary'

Note

In order for the primary and the secondary DHCP server to keep their lease tables in sync, they must be able to reach each other on TCP port 647. If you have firewall rules in effect, adjust them accordingly.

Static mappings MAC/IP

set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 static-mapping static-mapping-01 ip-address 172.16.17.10
set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 static-mapping static-mapping-01 mac-address ff:ff:ff:ff:ff:ff

DHCP server options

default-router (DHCP option 003)
set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 default-router <ROUTER-IP>
dns-server (DHCP option 006)
set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 dns-server <DNS-SERVER-IP>
domain-name Client domain name (DHCP option 015)
set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 domain-name "<DOMAIN-NAME>"
domain-search (DHCP option 119)
This option can be given multiple times if you need multiple search domains set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 domain-search "<DOMAIN_NAME_1>" set service dhcp-server shared-network-name dhcpexample subnet 172.16.17.0/24 domain-search "<DOMAIN_NAME_2>"