DHCP Server¶

The DHCPv4 server provides automatic IP address assignment and network configuration for clients. It supports address pools, static host assignments, and customizable DHCP options. It also serves as a DNS proxy for local subnets and can even forward queries to upstream DNS servers¹.

Note

When using the CLI, the system automatically enables essential options like DNS servers and default gateway based on the system's network configuration. These options can be disabled, changed or overridden, at any level: global, subnet, or per-host.

Basic Configuration¶

The following example configures a DHCP server for subnet 192.168.2.0/24 with an address pool:

admin@example:/> configure
admin@example:/config/> edit dhcp-server
admin@example:/config/dhcp-server/> edit subnet 192.168.2.0/24
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/> set pool start-address 192.168.2.100 end-address 192.168.2.200
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/> leave

When setting up the server from the CLI, the system automatically adds a few default DHCP options that will be sent to clients: both DNS server and default gateway will use the system address on the matching interface.

admin@example:/> show running-config
  "infix-dhcp-server:dhcp-server": {
    "subnet": [
      {
        "subnet": "192.168.2.0/24",
        "option": [
          {
            "id": "dns-server",
            "address": "auto"
          },
          {
            "id": "router",
            "address": "auto"
          }
        ],
        "pool": {
          "start-address": "192.168.2.100",
          "end-address": "192.168.2.200"
        }
      }
    ]
  }

Important

Remember to set up an interface in this subnet, avoid using addresses in the DHCP pool, or reserved for static hosts. In Class C networks the router usually has address .1. Depending on the use-case, you may also want to set up routing.

Static Host Assignment¶

To reserve specific IP addresses for clients based on their MAC address, hostname, or client ID:

admin@example:/config/dhcp-server/subnet/192.168.2.0/24/> edit host 192.168.2.10
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/host/192.168.2.10/> set match mac-address 00:11:22:33:44:55
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/host/192.168.2.10/> set hostname printer
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/host/192.168.2.10/> leave

Match hosts using a client identifier instead of MAC address:

admin@example:/config/dhcp-server/subnet/192.168.1.0/24/> edit host 192.168.1.50
admin@example:/config/dhcp-server/subnet/192.168.1.0/24/host/192.168.1.50/> edit match
admin@example:/config/dhcp-server/subnet/192.168.1.0/24/host/192.168.1.50/match/> set client-id hex c0:ff:ee
admin@example:/config/dhcp-server/subnet/192.168.1.0/24/host/192.168.1.50/match/> leave
admin@example:/config/dhcp-server/subnet/192.168.1.0/24/host/192.168.1.50/> set lease-time infinite
admin@example:/config/dhcp-server/subnet/192.168.1.0/24/host/192.168.1.50/> leave

The hex prefix here ensures matching of client ID is done using the hexadecimal octets c0:ff:ee, three bytes. Without the prefix the ASCII string "c0:ff:ee", eight bytes, is used.

Note

The DHCP server is fully RFC conformant, in the case of option 61 this means that using the hex prefix will require the client to set the htype field of the option to 00. See RFC 2132 for details.

Custom DHCP Options¶

Configure additional DHCP options globally, per subnet, or per host:

admin@example:/config/dhcp-server/> edit subnet 192.168.2.0/24
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/> edit option dns-server
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/option/dns-server/> set address 8.8.8.8
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/option/dns-server/> leave
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/> edit option ntp-server
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/option/ntp-server/> set address 192.168.2.1
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/option/ntp-server/> leave

When configuring, e.g., dns-server, or router options with the value auto, the system uses the IP address from the interface matching the subnet. For example:

admin@example:/> show interfaces brief
Interface    Status  Address
eth0         UP      192.168.1.1/24
eth1         UP      192.168.2.1/24

admin@example:/config/dhcp-server/subnet/192.168.1.0/24/> edit option dns-server
admin@example:/config/dhcp-server/subnet/192.168.1.0/24/option/dns-server/> set address auto
admin@example:/config/dhcp-server/subnet/192.168.1.0/24/option/dns-server/> leave

In this case, clients in subnet 192.168.1.0/24 will receive 192.168.1.1 as their DNS server address.

Multiple Subnets¶

Configure DHCP for multiple networks:

admin@example:/> configure
admin@example:/config/> edit dhcp-server
admin@example:/config/dhcp-server/> edit subnet 192.168.1.0/24
admin@example:/config/dhcp-server/subnet/192.168.1.0/24/> set pool start-address 192.168.1.100 end-address 192.168.1.200
admin@example:/config/dhcp-server/subnet/192.168.1.0/24/> leave
admin@example:/config/dhcp-server/> edit subnet 192.168.2.0/24
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/> set pool start-address 192.168.2.100 end-address 192.168.2.200
admin@example:/config/dhcp-server/subnet/192.168.2.0/24/> leave

Monitoring¶

View active leases and server statistics:

admin@example:/> show dhcp-server
IP ADDRESS       MAC                HOSTNAME            CLIENT ID             EXPIRES
192.168.2.22     00:a0:85:00:02:05                      00:c0:ff:ee           3591s
192.168.1.11     00:a0:85:00:04:06  foo                 01:00:a0:85:00:04:06  3591s

admin@example:/> show dhcp-server statistics
DHCP offers sent                : 6
DHCP ACK messages sent          : 5
DHCP NAK messages sent          : 0
DHCP decline messages received  : 0
DHCP discover messages received : 6
DHCP request messages received  : 5
DHCP release messages received  : 6
DHCP inform messages received   : 6

This requires the system DNS resolver to be configured. ↩