DHCP / DHCPv6

VyOS uses ISC DHCPd for both IPv4 and IPv6 address assignment.

DHCP Server

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

Basic Example

We are offering address space in the 192.0.2.0/24 network, which is physically connected on eth1, and pppoe0 is our connection to the internet. We are using the network name <name>.

Prerequisites:

  • Configuring PPPoE interface is assumed to be done already, and appears on pppoe0
  • Interface eth1 is configured to be connected to our DHCP subnet 192.0.2.0/24 by assigning e.g. address 192.0.2.1/24.

Multiple DHCP ranges can be defined and may contain holes.

set service dhcp-server shared-network-name '<name>' authoritative
set service dhcp-server shared-network-name '<name>' subnet 192.0.2.0/24 default-router 192.0.2.1
set service dhcp-server shared-network-name '<name>' subnet 192.0.2.0/24 dns-server 192.0.2.1
set service dhcp-server shared-network-name '<name>' subnet 192.0.2.0/24 lease 86400
set service dhcp-server shared-network-name '<name>' subnet 192.0.2.0/24 range 0 start 192.0.2.100
set service dhcp-server shared-network-name '<name>' subnet 192.0.2.0/24 range 0 stop 192.0.2.199

The generated config will look like:

[email protected]# show service dhcp-server shared-network-name '<name>'
authoritative
subnet 192.0.2.0/24 {
    default-router 192.0.2.1
    dns-server 192.0.2.1
    lease 86400
    range 0 {
        start 192.0.2.100
        stop 192.0.2.199
    }
}

Explanation

set service dhcp-server shared-network-name '<name>' 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 '<name>' subnet 192.0.2.0/24 default-router 192.0.2.1

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 '<name>' subnet 192.0.2.0/24 dns-server 192.0.2.1

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 '<name>' subnet 192.0.2.0/24 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 '<name>' subnet 192.0.2.0/24 range 0 start 192.0.2.100

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

set service dhcp-server shared-network-name '<name>' subnet 192.0.2.0/24 range 0 stop 192.0.2.199

[…] and ending at .199

Failover

VyOS provides support for DHCP failover. DHCP failover must be configured explicitly by the following statements.

set service dhcp-server shared-network-name 'LAN' subnet '192.0.2.0/24' failover local-address '192.0.2.1'

Local IP address used when communicating to the failover peer.

set service dhcp-server shared-network-name 'LAN' subnet '192.0.2.0/24' failover peer-address '192.0.2.2'

Peer IP address of the second DHCP server in this failover cluster.

set service dhcp-server shared-network-name 'LAN' subnet '192.0.2.0/24' failover name 'foo'

A generic name referencing this sync service.

Note

name must be identical on both sides!

set service dhcp-server shared-network-name 'LAN' subnet '192.0.2.0/24' failover status '{primary|secondary}'

The primary and secondary statements determines whether the server is primary r 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.

Hint

The dialogue between failover partners is neither encrypted nor authenticated. Since most DHCP servers exist within an organisation’s own secure Intranet, this would be an unnecessary overhead. However, if you have DHCP failover peers whose communications traverse insecure networks, then we recommend that you consider the use of VPN tunneling between them to ensure that the failover partnership is immune to disruption (accidental or otherwise) via third parties.

Static mappings

You can specify a static DHCP assignment on a per host basis. You will need the MAC address of the station and your desired IP address. The address must be inside your subnet definition but can be outside of your range sttement.

set service dhcp-server shared-network-name '<name>' subnet 192.0.2.0/24 static-mapping <host> ip-address 192.0.2.10

Configure desired IPv4 address for your host referenced to as host.

set service dhcp-server shared-network-name '<name>' subnet 192.0.2.0/24 static-mapping <hodt> mac-address ff:ff:ff:ff:ff:ff

Configure MAC address for your host referenced by as host used in this static assignment.

DHCP Options

set service dhcp-server shared-network-name '<name>' subnet 192.0.2.0/24 default-router '<address>'

Specify the default routers IPv4 address which should be used in this subnet. This can - of course - be a VRRP address (DHCP option 003).

set service dhcp-server shared-network-name '<name>' subnet 192.0.2.0/24 dns-server '<address>'

Specify the DNS nameservers used (Option 006). This option may be used mulltiple times to specify additional DNS nameservers.

set service dhcp-server shared-network-name '<name>' subnet 192.0.2.0/24 domain-name '<domain-name>'

The domain-name parameter should be the domain name that will be appended to the client’s hostname to form a fully-qualified domain-name (FQDN) (DHCP Option 015).

set service dhcp-server shared-network-name '<name>' subnet 192.0.2.0/24 domain-search '<domain-name>'

The domain-name parameter should be the domain name used when completing DNS request where no full FQDN is passed. This option can be given multiple times if you need multiple search domains (DHCP Option 119).

DHCPv6 Server

VyOS also provides DHCPv6 server functionality which is described in this section.

Configuration Options

set service dhcpv6-server preference <preference value>

Clients receiving advertise messages from multiple servers choose the server with the highest preference value. The range for this value is 0...255.

set service dhcpv6-server shared-network-name '<name>' subnet '<v6net>' lease-time {default | maximum | minimum}

The default lease time for DHCPv6 leases is 24 hours. This can be changed by supplying a default-time, maximum-time and minimum-time. All values need to be supplied in seconds.

set service dhcpv6-server shared-network-name '<name>' subnet '<v6net>' nis-domain '<domain-name>'

A NIS domain can be set to be used for DHCPv6 clients.

set service dhcpv6-server shared-network-name '<name>' subnet '<v6net>' nisplus-domain '<domain-name>'

The procedure to specify a NIS+ domain is similar to the NIS domain one:

set service dhcpv6-server shared-network-name '<name>' subnet '<v6net>' nis-server '<address>'

Specify a NIS server address for DHCPv6 clients.

set service dhcpv6-server shared-network-name '<name>' subnet '<v6net>' nisplus-server '<address>'

Specify a NIS+ server address for DHCPv6 clients.

set service dhcpv6-server shared-network-name '<name>' subnet '<v6net>' sip-server-address '<address>'

Specify a SIP server by IPv6 address for all DHCPv6 clients.

set service dhcpv6-server shared-network-name '<name>' subnet '<v6net>' sip-server-name '<fqdn>'

Specify a SIP server by FQDN for all DHCPv6 clients.

set service dhcpv6-server shared-network-name '<name>' subnet '<v6net>' sntp-server-address '<address>'

A SNTP server address can be specified for DHCPv6 clients:

Address pools

DHCPv6 address pools must be configured for the system to act as a DHCPv6 server. The following example describes a common scenario.

Example:

  • A shared network named NET1 serves subnet 2001:db8::/64
  • It is connected to eth1
  • DNS server is located at 2001:db8::ffff
  • Address pool shall be 2001:db8::100 through 2001:db8::199.
  • Lease time will be left at the default value which is 24 hours
set service dhcpv6-server shared-network-name 'NET1' subnet 2001:db8::/64 address-range start 2001:db8::100 stop 2001:db8::199
set service dhcpv6-server shared-network-name 'NET1' subnet 2001:db8::/64 name-server 2001:db8::ffff

The configuration will look as follows:

show service dhcpv6-server
    shared-network-name NET1 {
        subnet 2001:db8::/64 {
           address-range {
              start 2001:db8::100 {
                 stop 2001:db8::199
              }
           }
           name-server 2001:db8::ffff
        }
    }

Static mappings

In order to map specific IPv6 addresses to specific hosts static mappings can be created. The following example explains the process.

Example:

  • IPv6 address 2001:db8::101 shall be statically mapped
  • Device MAC address will be 00:53:c5:b7:5e:23
  • Host specific mapping shall be named client1

Hint

The MAC address identifier is defined by the last 4 byte of the MAC address.

set service dhcpv6-server shared-network-name 'NET1' subnet 2001:db8::/64 static-mapping client1 ipv6-address 2001:db8::101
set service dhcpv6-server shared-network-name 'NET1' subnet 2001:db8::/64 static-mapping client1 identifier c5b75e23

The configuration will look as follows:

show service dhcp-server shared-network-name NET1
   shared-network-name NET1 {
       subnet 2001:db8::/64 {
          name-server 2001:db8:111::111
          address-range {
              start 2001:db8::100 {
                 stop 2001:db8::199 {
              }
          }
          static-mapping client1 {
             ipv6-address 2001:db8::101
             identifier c5b75e23
          }
       }
    }

Operation Mode

restart dhcpv6 server

To restart the DHCPv6 server

show dhcpv6 server status

To show the current status of the DHCPv6 server.

show dhcpv6 server leases

Show statuses of all assigned leases:

DHCP Relay

If you want your router to forward DHCP requests to an external DHCP server you can configure the system to act as a DHCP relay agent. The DHCP relay agent works with IPv4 and IPv6 addresses.

All interfaces used for the DHCP relay must be configured. See https://wiki.vyos.net/wiki/Network_address_setup.

Configuration

set service dhcp-relay interface '<interface>'

Enable the DHCP relay service on the given interface.

set service dhcp-relay server 10.0.1.4

Configure IP address of the DHCP server

set service dhcp-relay relay-options relay-agents-packets discard

The router should discard DHCP packages already containing relay agent information to ensure that only requests from DHCP clients are forwarded.

Example

  • Use interfaces eth1 and eth2 for DHCP relay
  • Router receives DHCP client requests on eth1 and relays them through eth2
  • DHCP server is located at IPv4 address 10.0.1.4.
DHCP relay example

DHCP relay example

The generated configuration will look like:

show service dhcp-relay
    interface eth1
    interface eth2
    server 10.0.1.4
    relay-options {
       relay-agents-packets discard
    }

Options

set service dhcp-relay relay-options hop-count 'count'

Set the maximum hop count before packets are discarded. Range 0…255, default 10.

set service dhcp-relay relay-options max-size 'size'

Set maximum size of DHCP packets including relay agent information. If a DHCP packet size surpasses this value it will be forwarded without appending relay agent information. Range 64…1400, default 576.

set service dhcp-relay relay-options relay-agents-packet 'policy'

Four policies for reforwarding DHCP packets exist:

  • append: The relay agent is allowed to append its own relay information to a received DHCP packet, disregarding relay information already present in the packet.
  • discard: Received packets which already contain relay information will be discarded.
  • forward: All packets are forwarded, relay information already present will be ignored.
  • replace: Relay information already present in a packet is stripped and replaced with the router’s own relay information set.

Operation

restart dhcp relay-agent

Restart DHCP relay service

DHCPv6 relay

Configuration

set service dhcpv6-relay listen-interface eth1

Set eth1 to be the listening interface for the DHCPv6 relay:

set service dhcpv6-relay upstream-interface eth2 address 2001:db8::4

Set eth2 to be the upstream interface and specify the IPv6 address of the DHCPv6 server:

Example

  • DHCPv6 requests are received by the router on listening interface eth1
  • Requests are forwarded through eth2 as the upstream interface
  • External DHCPv6 server is at 2001:db8::4
DHCPv6 relay example

DHCPv6 relay example

The generated configuration will look like:

commit
show service dhcpv6-relay
    listen-interface eth1 {
    }
    upstream-interface eth2 {
       address 2001:db8::4
    }

Options

set service dhcpv6-relay max-hop-count 'count'

Set maximum hop count before packets are discarded, default: 10

set service dhcpv6-relay use-interface-id-option

If this is set the relay agent will insert the interface ID. This option is set automatically if more than one listening interfaces are in use.

Operation

show dhcpv6 relay-agent status

Show the current status of the DHCPv6 relay agent:

restart dhcpv6 relay-agent

Restart DHCPv6 relay agent immediately.