DHCP / DHCPv6

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

DHCP 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 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> 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> dns-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 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).

Failover

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

set service dhcp-server shared-network-name <name> subnet <subnet> failover local-address <address>
Local IP <address> used when communicating to the failover peer.
set service dhcp-server shared-network-name <name> subnet <subnet> failover peer-address <address>
Remote peer IP <address> of the second DHCP server in this failover cluster.
set service dhcp-server shared-network-name <name> subnet <subnet> failover name <name>

A generic <name> referencing this sync service.

Note

<name> must be identical on both sides!

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

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
dns-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
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.

Raw Parameters

Raw parameters can be passed to shared-network-name, subnet and static-mapping:

set service dhcp-server shared-network-name <name> shared-network-parameters
   <text>       Additional shared-network parameters for DHCP server.
set service dhcp-server shared-network-name <name> subnet <subnet> subnet-parameters
   <text>       Additional subnet parameters for DHCP server.
set service dhcp-server shared-network-name <name> subnet <subnet> static-mapping <description> static-mapping-parameters
   <text>       Additional static-mapping parameters for DHCP server.
                Will be placed inside the "host" block of the mapping.

These parameters are passed as-is to isc-dhcp’s dhcpd.conf under the configuration node they are defined in. They are not validated so an error in the raw parameters won’t be caught by vyos’s scripts and will cause dhcpd to fail to start. Always verify that the parameters are correct before committing the configuration. Refer to isc-dhcp’s dhcpd.conf manual for more information: https://kb.isc.org/docs/isc-dhcp-44-manual-pages-dhcpdconf

Quotes can be used inside parameter values by replacing all quote characters with the string &quot;. They will be replaced with literal quote characters when generating dhcpd.conf.

Example

Quick-Start
  • We are offering address space in the 192.0.2.0/24 network.
  • We are using the network name mypool.
set service dhcp-server shared-network-name mypool authoritative
set service dhcp-server shared-network-name mypool subnet 192.0.2.0/24 default-router 192.0.2.1
set service dhcp-server shared-network-name mypool subnet 192.0.2.0/24 dns-server 192.0.2.1
set service dhcp-server shared-network-name mypool subnet 192.0.2.0/24 lease 86400
set service dhcp-server shared-network-name mypool subnet 192.0.2.0/24 range 0 start 192.0.2.100
set service dhcp-server shared-network-name mypool 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 mypool
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
    }
}
Failover
  • Setup DHCP failover for network 192.0.2.0/24
  • 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

Primary

set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 default-router '192.0.2.254'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 dns-server '192.0.2.254'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 domain-name 'vyos.net'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 failover local-address '192.168.189.252'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 failover name 'NET-VYOS'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 failover peer-address '192.168.189.253'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 failover status 'primary'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 range 0 start '192.168.189.10'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 range 0 stop '192.168.189.250'

Secondary

set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 default-router '192.0.2.254'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 dns-server '192.0.2.254'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 domain-name 'vyos.net'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 failover local-address '192.168.189.253'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 failover name 'NET-VYOS'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 failover peer-address '192.168.189.252'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 failover status 'primary'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 range 0 start '192.168.189.10'
set service dhcp-server shared-network-name NET-VYOS subnet 192.0.2.0/24 range 0 stop '192.168.189.250'
Raw Parameters
  • Override static-mapping’s dns-server with a custom one that will be sent only to this host.
  • An option that takes a quoted string is set by replacing all quote characters with the string &quot; inside the static-mapping-parameters value. The resulting line in dhcpd.conf will be option pxelinux.configfile "pxelinux.cfg/01-00-15-17-44-2d-aa";.
set service dhcp-server shared-network-name dhcpexample subnet 192.0.2.0/24 static-mapping example static-mapping-parameters "option domain-name-servers 192.0.2.11, 192.0.2.12;"
set service dhcp-server shared-network-name dhcpexample subnet 192.0.2.0/24 static-mapping example static-mapping-parameters "option pxelinux.configfile &quot;pxelinux.cfg/01-00-15-17-44-2d-aa&quot;;"

Operation Mode

restart dhcp server
Restart the DHCP server
show dhcp server statistics
Show the DHCP server statistics:
[email protected]:~$ 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:
[email protected]:~$ show dhcp server leases
IP address      Hardware address    State    Lease start          Lease expiration     Remaining   Pool         Hostname
--------------  ------------------  -------  -------------------  -------------------  ----------  -----------  ---------
192.0.2.104     aa:bb:cc:dd:ee:ff   active   2019/12/05 14:24:23  2019/12/06 02:24:23  6:05:35     dhcpexample  test1
192.0.2.115     ab:ac:ad:ae:af:bf   active   2019/12/05 18:02:37  2019/12/06 06:02:37  9:43:49     dhcpexample  test2

Hint

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

show dhcp server leases pool <pool>
Show only leases in the specified pool.
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)

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 <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> 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> 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> nis-server <address>
Specify a NIS server address for DHCPv6 clients.
set service dhcpv6-server shared-network-name <name> subnet <prefix> nisplus-server <address>
Specify a NIS+ server address for DHCPv6 clients.
set service dhcpv6-server shared-network-name <name> subnet <prefix> sip-server-address <address>
Specify a SIP server by IPv6 address for all DHCPv6 clients.
set service dhcpv6-server shared-network-name <name> subnet <prefix> sip-server-name <fqdn>
Specify a SIP server by FQDN for all DHCPv6 clients.
set service dhcpv6-server shared-network-name <name> subnet <prefix> 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
  • 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 identifier 00:01:00:01:12:34:56:78:aa:bb:cc:dd:ee:ff

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 00:01:00:01:12:34:56:78:aa:bb:cc:dd:ee:ff
          }
       }
    }

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:
[email protected]:~$ show dhcpv6 server leases
IPv6 address   State    Last communication    Lease expiration     Remaining    Type           Pool   IAID_DUID
-------------  -------  --------------------  -------------------  -----------  -------------  -----  --------------------------------------------
2001:db8::101  active   2019/12/05 19:40:10   2019/12/06 07:40:10  11:45:21     non-temporary  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      non-temporary  NET1   87:65:43:21:00:01:00:01:11:22:33:44:fa:fb:fc:fd:fe: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)

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 <append | discard | forward | replace>

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 <interface>

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

Multiple interfaces may be specified.

set service dhcpv6-relay upstream-interface <interface> address <server>
Specifies an upstream network <interface> from which replies from <server> and other relay agents will be accepted.

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.