Pull request: DHCP: describe options
Merge in DNS/adguard-home-wiki from 4705-imp-opts to master
Squashed commit of the following:
commit e9ad1c83b8322ae8dbe6d8a388ca80d62bc75ae2
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date: Mon Sep 5 16:32:30 2022 +0300
DHCP: fix typos, imp wording
commit bff0e56383fd2f7d57684ac1ea6a22f8e6b90c9f
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date: Mon Sep 5 13:21:12 2022 +0300
DHCP: imp docs
commit eff212579b8b590475ab9a916353aaa5d73afd99
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date: Sat Sep 3 17:31:41 2022 +0300
DHCP: desc options
Eugene Burkov
parent
6818cc75dd
commit
7aadbbfcbb
187
DHCP.md
187
DHCP.md
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@ -38,101 +38,159 @@ below.
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### <a id="config-4" href="#config-4">The `dhcp.dhcpv4.options` Array Field</a>
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The `options` field accepts four types of values: `hex`, `ip`, `ips`, and
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`text`. They all start with the `CODE`, which MUST be an integer in the [1,
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255] range. See also [RFC 2132, sec. 3][rfc-2132].
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In accordance with [RFC 2131, sec. 4.3.1][rfc-2131], these options override the
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default options' values set by Adguard Home and requested by a client. Which
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means that if you want to set DNS server addresses using option `6`, you should
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The `options` field is used to explicitly specify the values for DHCP options
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and modify the response. In accordance with *Section 4.3.1* of [RFC
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2131][rfc-2131], these options override the default options' values set by
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Adguard Home and requested by a client. Which means that if you want to set
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custom DNS server addresses using option `6` (Domain Name Server), you may want
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also add Adguard Home's own addresses there. Otherwise, AdGuard Home's
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filtering won't work for the DHCP clients who receive these DNS server
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addresses.
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Option `del` has been added in **v0.107.12**. It is used to unconditionally
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remove options from the server's responses, which may lead to weird behaviors.
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Use with caution. On example where this option is useful is when a client
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doesn't accept a lease because of an option, see [issue 4337].
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Any option begins with an option *code* written as decimal integer. See [RFC
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2132][rfc-2132] for the actual DHCP option codes and allowed lengths. The code
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is followed by an option's *type* and *value*. Currently the following *types*
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are supported:
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* The `hex` format is:
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* `bool` (since **v0.107.12**) accepts a human-readable form of a boolean
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value, and has the length of 1 octet.
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```
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CODE hex HEX_VALUE
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```
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For example, to set option `6`, the DNS server, to two IP addresses,
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`1.2.3.4` and `1.2.3.5`, use:
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For example:
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```yaml
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# …
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'dhcp':
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# …
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'dhcpv4':
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# …
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'options':
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- '6 hex 0102030401020305'
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- '19 bool 0' # Disable IP forwarding for hosts.
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- '20 bool t' # Enable non-local source routing for hosts.
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- '27 bool F' # Disable ahoming for hosts.
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- '30 bool true' # Enable mask supplying for supporting hosts.
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- '36 bool False' # Make the hosts use RFC 894 for ethernet encapsulation.
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```
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* The `ip` format is:
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* `del` (since **v0.107.12**) is a no-value option and is used to
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unconditionally remove options from the server's responses (which may lead
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to weird behaviors, use with caution).
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```
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CODE ip IPV4_VALUE
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```
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For example, to set option `6`, the DNS server, to one IP address,
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`1.2.3.4`, use:
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Since the list of options is interpreted sequentially from first to last,
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the subsequent option may override the previous ones. So this:
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```yaml
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# …
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'dhcp':
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# …
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'dhcpv4':
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# …
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'options':
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- '6 ip 1.2.3.4'
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- '19 bool T'
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- '19 del'
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- '20 del'
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- '20 bool F'
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```
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* The `ips` format (since **v0.106.0**) is the same, but with comma-separated
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IP-addresses:
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instructs to remove the option `19`, and to set the option `20` to `false`.
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* `dur` (since **v0.107.12**) accepts a human-readable form of a duration in
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range [0 – 4294967296 seconds (about 136 days)] and has a length of *4*
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octets, just like a 32-bit unsigned integer.
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Here is the example of setting the MTU aging timeout to 10 minutes:
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```yaml
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# …
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'dhcp':
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# …
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'dhcpv4':
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# …
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'options':
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- '6 ips 1.2.3.4,5.6.7.8'
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- '24 dur 10m'
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```
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* The `text` format (since **v0.106.0**) allows you to put arbitrary UTF-8
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text as the option data. For example:
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* `hex` accepts a sequence of hexadecimal numbers of an arbitrary length.
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Here is the example of setting the plateau table for path MTU timeouts:
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```yaml
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# …
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'dhcp':
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# …
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'dhcpv4':
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# …
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'options':
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- '252 text http://example.com'
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- '25 hex 0044012801FC03EE05D407D211001FE645FA'
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```
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* The `del` format (since **v0.107.12**) allows you to remove an option. For
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example:
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* `ip` accepts an IPv4 address and has a length of *4* octets, just like an
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IPv4 itself.
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Here is the example of setting a broadcast address option:
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```yaml
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# …
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'dhcp':
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# …
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'dhcpv4':
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# …
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'options':
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- '61 del'
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- '28 ip 192.168.0.255'
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```
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[issue 4337]: https://github.com/adguardTeam/adGuardHome/issues/4337
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* `ips` (since **v0.106.0**) accepts a comma-separated list if IPv4 addresses.
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It has an arbitrary length, but is always a multiple of *4* octets.
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Here is the example of setting the domain name servers to `1.2.3.4` and
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`1.2.3.5`:
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```yaml
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'options':
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- '6 ips 1.2.3.4,1.2.3.5'
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```
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* `text` (since **v0.106.0**) accepts an arbitrary UTF-8 encoded string and
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has a length of encoded text.
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Here is the example of setting the path to configuration file for WPAD:
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```yaml
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'options':
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- '252 text http://server.domain/proxyconfig.pac'
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```
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* `u8` (since **v0.107.12**) accepts a decimal number in range [0 – 255] and
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takes *1* octet, just like an unsigned 8-bit integer.
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Here is the example of setting the TTL for Internet Protocol:
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```yaml
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'options':
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- '23 u8 64'
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```
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* `u16` (since **v0.107.12**) accepts a decimal number in range [0 – 65535]
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and takes *2* octets, just like an unsigned 16-bit integer.
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Here is the example of setting the maximum datagram reassembly size to 576
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bytes:
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```yaml
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'options':
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- '22 u16 576'
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```
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**NOTE:** Thoroughly check that the option format and value are valid for the
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chosen type in accordance with [RFC 2132][rfc-2132] or others. AdGuard Home does
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not perform any option-specific validations.
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Currently there is a set of options listed in *Appendix A* of [RFC
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2131][rfc-2131] with the default values chosen according to the documents
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mentioned there:
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| Option | Value |
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| -------------------------------- | --------------------------------------------- |
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| IP Forwarding | Disabled |
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| Non-Local Source Routing | Disabled |
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| Maximum Datagram Reassembly Size | 576 bytes |
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| Default IP Time-to-live | 64 seconds |
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| Path MTU Aging Timeout Option | 10 minutes |
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| Path MTU Plateau Table | See [Table 7.1 in RFC 1191][rfc-1191-tbl-7.1] |
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| Interface MTU | 576 bytes |
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| All subnets are local | False |
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| Perform Mask Discovery | False |
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| Mask Supplier | False |
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| Perform Router Discovery | True |
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| Router Solicitation Address | 224.0.0.2 |
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| Broadcast Address | 255.255.255.255 |
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| Use Trailer Encapsulation | False |
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| ARP Cache Timeout | 1 minute |
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| Ethernet Encapsulation version | RFC 894 |
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| Default TCP TTL | 60 seconds |
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| TCP Keepalive Interval | 2 hours |
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| Put TCP Keepalive Garbage | True |
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| Routers | `gateway_ip` from configuration |
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| Subnet Mask | `subnet_mask` from configuration |
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Some of these values may appear obsolete or may cause issues with some DHCP
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client implementations among the many existing. In accordance with [RFC
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2131][rfc-2131] the options, when not explicitly configured, are only returned
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if requested by client within the option `55` (Parameter Request List).
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### <a id="config-6" href="#config-6">DHCPv6 Options</a>
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@ -144,8 +202,9 @@ The option `dhcp.dhcpv6.ra_allow_slaac`, if `true`, sends RA packets allowing
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the clients to choose between SLAAC and DHCPv6.
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[configuration]: https://github.com/AdguardTeam/AdGuardHome/wiki/Configuration
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[rfc-2131]: https://tools.ietf.org/html/rfc2131#page-29
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[rfc-2132]: https://tools.ietf.org/html/rfc2132#section-3
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[rfc-1191-tbl-7.1]: https://datatracker.ietf.org/doc/html/rfc1191#section-7.1
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[rfc-2131]: https://datatracker.ietf.org/doc/html/rfc2131
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[rfc-2132]: https://datatracker.ietf.org/doc/html/rfc2132
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