Skip to content

DHCP

Jump to bottom
Stanislav Chzhen edited this page Apr 18, 2023 · 11 revisions

AdGuard Home - DHCP server

AdGuard Home can be used as a DHCP server. This page describes how to do that.

Prerequisites

  1. Make sure that you run an OS on which AdGuard Home supports DHCP. We currently don't support DHCP on Windows.

  2. Make sure that your machine has a static IP address.

Default options

By default, AdGuard Home will set itself as the DNS server for the DHCP clients. The default lease time is 24 hours.

Configuration

See the DHCP section in the configuration article for the overview of the DHCP configuration options. There are several configuration parameters for DHCP that can't be set via the AdGuard Home administrator dashboard. Those are described below.

The dhcp.dhcpv4.options array field

The options field is used to explicitly specify the values for DHCP options and modify the response. In accordance with Section 4.3.1 of RFC 2131, these options override the default options' values set by Adguard Home and requested by a client. Which means that if you want to set custom DNS server addresses using option 6 (Domain Name Server), you may want also add Adguard Home's own addresses there. Otherwise, AdGuard Home's filtering won't work for the DHCP clients who receive these DNS server addresses.

Any option begins with an option code written as decimal integer. See RFC 2132 for the actual DHCP option codes and allowed lengths. The code is followed by an option's type and value. Currently the following types are supported:

  • bool (since v0.107.12) accepts a human-readable form of a boolean value, and has the length of 1 octet.

    For example:

    'options':
- '19 bool 0'     # Disable IP forwarding for hosts.
- '20 bool t'     # Enable non-local source routing for hosts.
- '27 bool F'     # Disable ahoming for hosts.
- '30 bool true'  # Enable mask supplying for supporting hosts.
- '36 bool False' # Make the hosts use RFC 894 for ethernet encapsulation.

  • del (since v0.107.12) is a no-value option and is used to unconditionally remove options from the server's responses (which may lead to weird behaviors, use with caution).

    Since the list of options is interpreted sequentially from first to last, the subsequent option may override the previous ones. So this:

    'options':
- '19 bool T'
- '19 del'
- '20 del'
- '20 bool F'

    instructs to remove the option 19, and to set the option 20 to false.

  • dur (since v0.107.12) accepts a human-readable form of a duration in range [0 – 4294967296 seconds (about 136 days)] and has a length of 4 octets, just like a 32-bit unsigned integer.

    Here is the example of setting the MTU aging timeout to 10 minutes:

    'options':
- '24 dur 10m'

  • hex accepts a sequence of hexadecimal numbers of an arbitrary length.

    Here is the example of setting the plateau table for path MTU timeouts:

    'options':
- '25 hex 0044012801FC03EE05D407D211001FE645FA'

  • ip accepts an IPv4 address and has a length of 4 octets, just like an IPv4 itself.

    Here is the example of setting a broadcast address option:

    'options':
- '28 ip 192.168.0.255'

  • ips (since v0.106.0) accepts a comma-separated list if IPv4 addresses. It has an arbitrary length, but is always a multiple of 4 octets.

    Here is the example of setting the domain name servers to 1.2.3.4 and 1.2.3.5:

    'options':
- '6 ips 1.2.3.4,1.2.3.5'

  • text (since v0.106.0) accepts an arbitrary UTF-8 encoded string and has a length of encoded text.

    Here is the example of setting the path to configuration file for WPAD:

    'options':
- '252 text http://server.domain/proxyconfig.pac'

  • u8 (since v0.107.12) accepts a decimal number in range [0 – 255] and takes 1 octet, just like an unsigned 8-bit integer.

    Here is the example of setting the TTL for Internet Protocol:

    'options':
- '23 u8 64'

  • u16 (since v0.107.12) accepts a decimal number in range [0 – 65535] and takes 2 octets, just like an unsigned 16-bit integer.

    Here is the example of setting the maximum datagram reassembly size to 576 bytes:

    'options':
- '22 u16 576'

NOTE: Thoroughly check that the option format and value are valid for the chosen type in accordance with RFC 2132 or others. AdGuard Home does not perform any option-specific validations.

Currently there is a set of options listed in Appendix A of RFC 2131 with the default values chosen according to the documents mentioned there:

Option Value
IP Forwarding Disabled
Non-Local Source Routing Disabled
Maximum Datagram Reassembly Size 576 bytes
Default IP Time-to-live 64 seconds
Path MTU Aging Timeout Option 10 minutes
Path MTU Plateau Table See Table 7.1 in RFC 1191
Interface MTU 576 bytes
All subnets are local False
Perform Mask Discovery False
Mask Supplier False
Perform Router Discovery True
Router Solicitation Address 224.0.0.2
Broadcast Address 255.255.255.255
Use Trailer Encapsulation False
ARP Cache Timeout 1 minute
Ethernet Encapsulation version RFC 894
Default TCP TTL 60 seconds
TCP Keepalive Interval 2 hours
Put TCP Keepalive Garbage True
Routers gateway_ip from configuration
Subnet Mask subnet_mask from configuration

Some of these values may appear obsolete or may cause issues with some DHCP client implementations among the many existing. In accordance with RFC 2131 the options, when not explicitly configured, are only returned if requested by client within the option 55 (Parameter Request List).

DHCPv6 options

The option dhcp.dhcpv6.ra_slaac_only, if true, sends RA packets forcing the clients to use SLAAC. The DHCPv6 server won't be started in this case.

The option dhcp.dhcpv6.ra_allow_slaac, if true, sends RA packets allowing the clients to choose between SLAAC and DHCPv6.

Automatic hosts

Machines in the network can be reached more easily using the hostnames they send in the DHCP requests with a configurable top-level domain (TLD). By default, the TLD is lan. For example, if you have a machine called “workstation” in the network, and it sends a DHCP request with option 12 set to workstation, you can reach it over HTTP on the host http://workstation.lan.

You can also set a custom TLD or domain name using the dns.local_domain_name field in the configuration file.

Stored leases

DHCP leases stored in data/leases.json. The file format is not stable and may change in the future releases.

Guides

Clone this wiki locally