DHCP Server

VyOS uses Kea DHCP server for both IPv4 and IPv6 address assignment.

IPv4 server

The network topology is declared by shared-network-name and the subnet declarations. The DHCP service can serve multiple shared networks, with each shared network having 1 or more subnets. Each subnet must be present on an interface. A range can be declared inside a subnet to define a pool of dynamic addresses. Multiple ranges can be defined and can contain holes. Static mappings can be set to assign “static” addresses to clients based on their MAC address.

Configuration

set service dhcp-server hostfile-update

Create DNS record per client lease, by adding clients to /etc/hosts file. Entry will have format: <shared-network-name>_<hostname>.<domain-name>

set service dhcp-server shared-network-name <name> option 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).

This is the configuration parameter for the entire shared network definition. All subnets will inherit this configuration item if not specified locally.

set service dhcp-server shared-network-name <name> option 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).

This is the configuration parameter for the entire shared network definition. All subnets will inherit this configuration item if not specified locally.

set service dhcp-server shared-network-name <name> option name-server <address>

Inform client that the DNS server can be found at <address>.

This is the configuration parameter for the entire shared network definition. All subnets will inherit this configuration item if not specified locally. Multiple DNS servers can be defined.

set service dhcp-server shared-network-name <name> option vendor-option <option-name>

This configuration parameter lets you specify a vendor-option for the entire shared network definition. All subnets will inherit this configuration item if not specified locally. An example for Ubiquiti is shown below:

Example:

Pass address of Unifi controller at 172.16.100.1 to all clients of NET1

set service dhcp-server shared-network-name 'NET1' option vendor-option
ubiquiti '172.16.100.1'
set service dhcp-server listen-address <address>

This configuration parameter lets the DHCP server to listen for DHCP requests sent to the specified address, it is only realistically useful for a server whose only clients are reached via unicasts, such as via DHCP relay agents.

Individual Client Subnet

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 <subnet> subnet-id <id>

This configuration parameter is required and must be unique to each subnet. It is required to map subnets to lease file entries.

set service dhcp-server shared-network-name <name> subnet <subnet> option default-router <address>

This is a configuration parameter for the <subnet>, saying that as part of the response, tell the client that the default gateway can be reached at <address>.

set service dhcp-server shared-network-name <name> subnet <subnet> option name-server <address>

This is a configuration parameter for the subnet, saying that as part of the response, tell the client that the DNS server can be found at <address>.

Multiple DNS servers can be defined.

set service dhcp-server shared-network-name <name> subnet <subnet> lease <time>

Assign the IP address to this machine for <time> seconds.

The default value is 86400 seconds which corresponds to one day.

set service dhcp-server shared-network-name <name> subnet <subnet> range <n> start <address>

Create DHCP address range with a range id of <n>. DHCP leases are taken from this pool. The pool starts at address <address>.

set service dhcp-server shared-network-name <name> subnet <subnet> range <n> stop <address>

Create DHCP address range with a range id of <n>. DHCP leases are taken from this pool. The pool stops with address <address>.

set service dhcp-server shared-network-name <name> subnet <subnet> exclude <address>

Always exclude this address from any defined range. This address will never be assigned by the DHCP server.

This option can be specified multiple times.

set service dhcp-server shared-network-name <name> subnet <subnet> option 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 <subnet> option 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).

set service dhcp-server shared-network-name <name> subnet <subnet> option vendor-option <option-name>

This configuration parameter lets you specify a vendor-option for the subnet specified within the shared network definition. An example for Ubiquiti is shown below:

Example:

Create 172.18.201.0/24 as a subnet within NET1 and pass address of Unifi controller at 172.16.100.1 to clients of that subnet.

set service dhcp-server shared-network-name 'NET1' subnet
'172.18.201.0/24' option vendor-option ubiquiti '172.16.100.1'

High Availability

VyOS provides High Availability support for DHCP server. DHCP High Availability can act in two different modes:

  • Active-active: both DHCP servers will respond to DHCP requests. If mode is not defined, this is the default behavior.

  • Active-passive: only primary server will respond to DHCP requests. If this server goes offline, then secondary server will take place.

DHCP High Availability must be configured explicitly by the following statements on both servers:

set service dhcp-server high-availability mode [active-active | active-passive]

Define operation mode of High Availability feature. Default value if command is not specified is active-active

set service dhcp-server high-availability source-address <address>

Local IP <address> used when communicating to the HA peer.

set service dhcp-server high-availability remote <address>

Remote peer IP <address> of the second DHCP server in this HA cluster.

set service dhcp-server high-availability name <name>

A generic <name> referencing this sync service.

Note

<name> must be identical on both sides!

set service dhcp-server high-availability status <primary | secondary>

The primary and secondary statements determines whether the server is primary or 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 HA 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 HA peers whose communications traverse insecure networks, then we recommend that you consider the use of VPN tunneling between them to ensure that the HA 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 the subnet definition but can be outside of the range statement.

set service dhcp-server shared-network-name <name> subnet <subnet> static-mapping <description> mac <address>

Create a new DHCP static mapping named <description> which is valid for the host identified by its MAC <address>.

set service dhcp-server shared-network-name <name> subnet <subnet> static-mapping <description> duid <identifier>

Create a new DHCP static mapping named <description> which is valid for the host identified by its DHCP unique identifier (DUID) <identifier>.

set service dhcp-server shared-network-name <name> subnet <subnet> static-mapping <description> ip-address <address>

Static DHCP IP address assign to host identified by <description>. IP address must be inside the <subnet> which is defined but can be outside the dynamic range created with set service dhcp-server shared-network-name <name> subnet <subnet> range <n>. If no ip-address is specified, an IP from the dynamic pool is used.

This is useful, for example, in combination with hostfile update.

Hint

This is the equivalent of the host block in dhcpd.conf of isc-dhcpd.

Example:

  • IP address 192.168.1.100 shall be statically mapped to client named client1

set service dhcp-server shared-network-name 'NET1' subnet 192.168.1.0/24 subnet-id 1
set service dhcp-server shared-network-name 'NET1' subnet 192.168.1.0/24 static-mapping client1 ip-address 192.168.1.100
set service dhcp-server shared-network-name 'NET1' subnet 192.168.1.0/24 static-mapping client1 mac aa:bb:11:22:33:00

The configuration will look as follows:

show service dhcp-server shared-network-name NET1
 subnet 192.168.1.0/24 {
     static-mapping client1 {
         ip-address 192.168.1.100
         mac aa:bb:11:22:33:00
     }
     subnet-id 1
 }

Options

Setting name

Option number

ISC-DHCP Option name

Option description

Multi

client-prefix-length

1

subnet-mask

Specifies the clients subnet mask as per RFC 950. If unset, subnet declaration is used.

N

time-offset

2

time-offset

Offset of the client’s subnet in seconds from Coordinated Universal Time (UTC)

N

default-router

3

routers

IPv4 address of router on the client’s subnet

N

time-server

4

time-servers

RFC 868 time server IPv4 address

Y

name-server

6

domain-name-servers

DNS server IPv4 address

Y

domain-name

15

domain-name

Client domain name

Y

ip-forwarding

19

ip-forwarding

Enable IP forwarding on client

N

ntp-server

42

ntp-servers

IP address of NTP server

Y

wins-server

44

netbios-name-servers

NetBIOS over TCP/IP name server

Y

server-identifier

54

dhcp-server-identifier

IP address for DHCP server identifier

N

bootfile-server

siaddr

next-server

IPv4 address of next bootstrap server

N

tftp-server-name

66

tftp-server-name

Name or IPv4 address of TFTP server

N

bootfile-name

67

bootfile-name, filename

Bootstrap file name

N

bootfile-size

13

boot-size

Boot image length in 512-octet blocks

N

smtp-server

69

smtp-server

IP address of SMTP server

Y

pop-server

70

pop-server

IP address of POP3 server

Y

domain-search

119

domain-search

Client domain search

Y

static-route

121, 249

rfc3442-static-route, windows-static-route

Classless static route

N

wpad-url

252

wpad-url, wpad-url code 252 = text

Web Proxy Autodiscovery (WPAD) URL

N

lease

default-lease-time, max-lease-time

Lease timeout in seconds (default: 86400)

N

range

range

DHCP lease range

Y

exclude

IP address to exclude from DHCP lease range

Y

failover

DHCP failover parameters

static-mapping

Name of static mapping

Y

Multi: can be specified multiple times.

Example

Please see the DHCP/DNS quick-start configuration.

High Availability

Configuration of a DHCP HA pair:

  • Setup DHCP HA for network 192.0.2.0/24

  • Use active-active HA mode.

  • Default gateway and DNS server is at 192.0.2.254

  • The primary DHCP server uses address 192.168.189.252

  • The secondary DHCP server uses address 192.168.189.253

  • DHCP range spans from 192.168.189.10 - 192.168.189.250

Common configuration, valid for both primary and secondary node.

set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 option default-router '192.0.2.254'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 option name-server '192.0.2.254'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 option domain-name 'vyos.net'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 range 0 start '192.0.2.10'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 range 0 stop '192.0.2.250'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 subnet-id '1'

Primary

set service dhcp-server high-availability mode 'active-active'
set service dhcp-server high-availability source-address '192.168.189.252'
set service dhcp-server high-availability name 'NET-VYOS'
set service dhcp-server high-availability remote '192.168.189.253'
set service dhcp-server high-availability status 'primary'

Secondary

set service dhcp-server high-availability mode 'active-active'
set service dhcp-server high-availability source-address '192.168.189.253'
set service dhcp-server high-availability name 'NET-VYOS'
set service dhcp-server high-availability remote '192.168.189.252'
set service dhcp-server high-availability status 'secondary'

Operation Mode

show log dhcp server

Show DHCP server daemon log file

show log dhcp client

Show logs from all DHCP client processes.

show log dhcp client interface <interface>

Show logs from specific interface DHCP client process.

restart dhcp server

Restart the DHCP server

show dhcp server statistics

Show the DHCP server statistics:

vyos@vyos:~$ show dhcp server statistics
Pool           Size    Leases    Available  Usage
-----------  ------  --------  -----------  -------
dhcpexample      99         2           97  2%
show dhcp server statistics pool <pool>

Show the DHCP server statistics for the specified pool.

show dhcp server leases

Show statuses of all active leases:

vyos@vyos:~$ show dhcp server leases
IP Address      MAC address        State    Lease start          Lease expiration     Remaining    Pool      Hostname    Origin
--------------  -----------------  -------  -------------------  -------------------  -----------  --------  ----------  --------
192.168.11.134  00:50:79:66:68:09  active   2023/11/29 09:51:05  2023/11/29 10:21:05  0:24:10      LAN       VPCS1       local
192.168.11.133  50:00:00:06:00:00  active   2023/11/29 09:51:38  2023/11/29 10:21:38  0:24:43      LAN       VYOS-6      local
10.11.11.108    50:00:00:05:00:00  active   2023/11/29 09:51:43  2023/11/29 10:21:43  0:24:48      VIF-1001  VYOS5       local
192.168.11.135  00:50:79:66:68:07  active   2023/11/29 09:55:16  2023/11/29 09:59:16  0:02:21                            remote
vyos@vyos:~$

Hint

Static mappings aren’t shown. To show all states, use show dhcp server leases state all.

show dhcp server leases origin [local | remote]

Show statuses of all active leases granted by local (this server) or remote (failover server):

vyos@vyos:~$ show dhcp server leases origin remote
IP Address      MAC address        State    Lease start          Lease expiration     Remaining    Pool      Hostname    Origin
--------------  -----------------  -------  -------------------  -------------------  -----------  --------  ----------  --------
192.168.11.135  00:50:79:66:68:07  active   2023/11/29 09:55:16  2023/11/29 09:59:16  0:02:21                            remote
vyos@vyos:~$
show dhcp server leases pool <pool>

Show only leases in the specified pool.

vyos@vyos:~$ show dhcp server leases pool LAN
IP Address      MAC address        State    Lease start          Lease expiration     Remaining    Pool    Hostname    Origin
--------------  -----------------  -------  -------------------  -------------------  -----------  ------  ----------  --------
192.168.11.134  00:50:79:66:68:09  active   2023/11/29 09:51:05  2023/11/29 10:21:05  0:23:55      LAN     VPCS1       local
192.168.11.133  50:00:00:06:00:00  active   2023/11/29 09:51:38  2023/11/29 10:21:38  0:24:28      LAN     VYOS-6      local
vyos@vyos:~$
show dhcp server leases sort <key>

Sort the output by the specified key. Possible keys: ip, hardware_address, state, start, end, remaining, pool, hostname (default = ip)

show dhcp server leases state <state>

Show only leases with the specified state. Possible states: all, active, free, expired, released, abandoned, reset, backup (default = active)

IPv6 server

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

Configuration

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 <subnet> subnet-id <id>

This configuration parameter is required and must be unique to each subnet. It is required to map subnets to lease file entries.

set service dhcpv6-server shared-network-name <name> subnet <prefix> 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 <prefix> option 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 <prefix> option 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 <prefix> option nis-server <address>

Specify a NIS server address for DHCPv6 clients.

set service dhcpv6-server shared-network-name <name> subnet <prefix> option nisplus-server <address>

Specify a NIS+ server address for DHCPv6 clients.

set service dhcpv6-server shared-network-name <name> subnet <prefix> option sip-server <address | fqdn>

Specify a SIP server by IPv6 address of Fully Qualified Domain Name for all DHCPv6 clients.

set service dhcpv6-server shared-network-name <name> subnet <prefix> option sntp-server-address <address>

A SNTP server address can be specified for DHCPv6 clients.

Prefix Delegation

To hand out individual prefixes to your clients the following configuration is used:

set service dhcpv6-server shared-network-name <name> subnet <prefix> prefix-delegation prefix <pd-prefix> prefix-length <lenght>

Delegate prefixes from <pd-prefix> to clients in subnet <prefix>. Range is defined by <lenght> in bits, 32 to 64.

set service dhcpv6-server shared-network-name <name> subnet <prefix> prefix-delegation prefix <pd-prefix> delegated-length <lenght>

Hand out prefixes of size <length> in bits from <pd-prefix> to clients in subnet <prefix> when the request for prefix delegation.

set service dhcpv6-server shared-network-name <name> subnet <prefix> prefix-delegation prefix <pd-prefix> excluded-prefix <exclude-prefix>

Exclude <exclude-prefix> from <pd-prefix>.

set service dhcpv6-server shared-network-name <name> subnet <prefix> prefix-delegation prefix <pd-prefix> excluded-prefix-length <length>

Define lenght of exclude prefix in <pd-prefix>.

Example:

  • A shared network named PD-NET serves subnet 2001:db8::/64.

  • It is connected to eth1.

  • Address pool shall be 2001:db8::100 through 2001:db8::199.

  • It hands out prefixes 2001:db8:0:10::/64 through 2001:db8:0:1f::/64.

set service dhcpv6-server shared-network-name 'PD-NET' interface 'eth1'
set service dhcpv6-server shared-network-name 'PD-NET' subnet 2001:db8::/64 range 1 start 2001:db8::100
set service dhcpv6-server shared-network-name 'PD-NET' subnet 2001:db8::/64 range 1 stop 2001:db8::199
set service dhcpv6-server shared-network-name 'PD-NET' subnet 2001:db8::/64 prefix-delegation prefix 2001:db8:0:10:: delegated-length '64'
set service dhcpv6-server shared-network-name 'PD-NET' subnet 2001:db8::/64 prefix-delegation prefix 2001:db8:0:10:: prefix-length '60'

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 'NET' interface 'eth1'
set service dhcpv6-server shared-network-name 'NET1' subnet 2001:db8::/64 range 1 start 2001:db8::100
set service dhcpv6-server shared-network-name 'NET1' subnet 2001:db8::/64 range 1 stop 2001:db8::199
set service dhcpv6-server shared-network-name 'NET1' subnet 2001:db8::/64 option name-server 2001:db8::ffff
set service dhcpv6-server shared-network-name 'NET1' subnet 2001:db8::/64 subnet-id 1

The configuration will look as follows:

show service dhcpv6-server
    shared-network-name NET1 {
        subnet 2001:db8::/64 {
           range 1 {
              start 2001:db8::100
              stop 2001:db8::199
           }
           option {
              name-server 2001:db8::ffff
           }
           subnet-id 1
        }
    }

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

  • IPv6 prefix 2001:db8:0:101::/64 shall be statically mapped

  • Host specific mapping shall be named client1

Hint

The identifier is the device’s DUID: colon-separated hex list (as used by isc-dhcp option dhcpv6.client-id). If the device already has a dynamic lease from the DHCPv6 server, its DUID can be found with show service dhcpv6 server leases. The DUID begins at the 5th octet (after the 4th colon) of IAID_DUID.

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 ipv6-prefix 2001:db8:0:101::/64
set service dhcpv6-server shared-network-name 'NET1' subnet 2001:db8::/64 static-mapping client1 duid 00:01:00:01:12:34:56:78:aa:bb:cc:dd:ee:ff

The configuration will look as follows:

show service dhcpv6-server shared-network-name NET1
 subnet 2001:db8::/64 {
     static-mapping client1 {
         duid 00:01:00:01:12:34:56:78:aa:bb:cc:dd:ee:ff
         ipv6-address 2001:db8::101
         ipv6-prefix 2001:db8:0:101::/64
     }
 }

Operation Mode

show log dhcpv6 server

Show DHCPv6 server daemon log file

show log dhcpv6 client

Show logs from all DHCPv6 client processes.

show log dhcpv6 client interface <interface>

Show logs from specific interface DHCPv6 client process.

restart dhcpv6 server

To restart the DHCPv6 server

show dhcpv6 server leases

Shows status of all assigned leases:

vyos@vyos:~$ show dhcpv6 server leases
IPv6 address      State    Last communication    Lease expiration     Remaining    Type   Pool      DUID
----------------  -------  --------------------  -------------------  -----------  -----  --------  --------------------------------------------
2001:db8::101     active   2019/12/05 19:40:10   2019/12/06 07:40:10  11:45:21     IA_NA  NET1      98:76:54:32:00:01:00:01:12:34:56:78:aa:bb:cc:dd:ee:ff
2001:db8::102     active   2019/12/05 14:01:23   2019/12/06 02:01:23  6:06:34      IA_NA  NET1      87:65:43:21:00:01:00:01:11:22:33:44:fa:fb:fc:fd:fe:ff
2001:db8:10::/64  active   2019/12/05 23:20:10   2019/12/06 11:40:10  11:45:21     IA_PD  PD-NET1   98:76:54:32:00:01:00:01:12:34:56:78:aa:bb:cc:dd:ee:ff

Hint

Static mappings aren’t shown. To show all states, use show dhcp server leases state all.

show dhcpv6 server leases pool <pool>

Show only leases in the specified pool.

show dhcpv6 server leases sort <key>

Sort the output by the specified key. Possible keys: expires, iaid_duid, ip, last_comm, pool, remaining, state, type (default = ip)

show dhcpv6 server leases state <state>

Show only leases with the specified state. Possible states: abandoned, active, all, backup, expired, free, released, reset (default = active)