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doc: update networking guide with dhcpv6 details
Signed-off-by: Joachim Wiberg <[email protected]>
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‎doc/networking.md‎

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@@ -959,16 +959,55 @@ Client Configuration](system.md#ntp-client-configuration) section.
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Multiple address assignment methods are available:
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| **Type** | **Yang Model** | **Description** |
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|:---------------- |:-------------- |:------------------------------------------------------------------------------------------------------------------------------------------------- |
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| static | ietf-ip | Static assignment of IPv6 address, e.g., *2001:db8:0:1::1/64* |
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| link-local | ietf-ip[^2] | (RFC4862) Auto-configured link-local IPv6 address (*fe80::0* prefix + interface identifier, e.g., *fe80::ccd2:82ff:fe52:728b/64*) |
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| global auto-conf | ietf-ip | (RFC4862) Auto-configured (stateless) global IPv6 address (prefix from router + interface identifier, e.g., *2001:db8:0:1:ccd2:82ff:fe52:728b/64* |
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| **Type** | **Yang Model** | **Description** |
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|:---------------- |:-------------------- |:------------------------------------------------------------------------------------------------------------------------------------------------- |
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| static | ietf-ip | Static assignment of IPv6 address, e.g., *2001:db8:0:1::1/64* |
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| link-local | ietf-ip[^2] | (RFC4862) Auto-configured link-local IPv6 address (*fe80::0* prefix + interface identifier, e.g., *fe80::ccd2:82ff:fe52:728b/64*) |
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| global auto-conf | ietf-ip | (RFC4862) Auto-configured (stateless) global IPv6 address (prefix from router + interface identifier, e.g., *2001:db8:0:1:ccd2:82ff:fe52:728b/64* |
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| dhcp | infix-dhcpv6-client | Assignment of IPv6 address by DHCPv6 server, e.g., *2001:db8::42/128* |
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Both for *link-local* and *global auto-configuration*, it is possible
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to auto-configure using a random suffix instead of the interface
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identifier.
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> [!NOTE]
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> The DHCPv6 address method is only available for *LAN* interfaces
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> (Ethernet, virtual Ethernet (veth), bridge, link aggregates, etc.)
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Supported DHCPv6 (request) options, configurability (Cfg) and defaults,
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are listed below. Configurable options can be disabled on a per client
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interface basis, some options, like `client-id` and `client-fqdn`, are
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possible to set the value of as well.
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| **Opt** | **Name** | **Cfg** | **Description** |
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|---------|----------------------------|---------|--------------------------------------------------------|
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| 1 | `client-id` | Yes | Client identifier (DUID), auto-generated by default |
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| 2 | `server-id` | Yes | Server identifier (DUID) |
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| 23 | `dns-server` | Yes | DNS recursive name servers, static ones take precedence|
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| 24 | `domain-search` | Yes | Domain search list |
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| 25 | `ia-pd` | Yes | Prefix delegation for downstream networks |
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| 31 | `sntp-server` | Yes | Simple Network Time Protocol servers |
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| 32 | `information-refresh-time` | Yes | Refresh time for stateless DHCPv6 |
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| 39 | `client-fqdn` | Yes | Client FQDN, request DNS update from server |
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| 56 | `ntp-server` | Yes | NTP time servers, static ones take precedence |
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| | | | |
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**Default:** `dns-server`, `domain-search`, `ntp-server`
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DHCPv6 supports both **stateful** (address assignment) and **stateless**
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(information-only) modes:
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- **Stateful DHCPv6**: The server assigns IPv6 addresses to clients. This is
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the default mode when enabling the DHCPv6 client.
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- **Stateless DHCPv6**: Used with SLAAC (Stateless Address Autoconfiguration)
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when only configuration information (DNS, NTP, etc.) is needed. Enable with
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the `information-only` setting.
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When configuring a DHCPv6 client, ensure that the NTP client is enabled
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for the `ntp-server` DHCPv6 option to be processed correctly. If the
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NTP client is not enabled, any NTP servers provided by the DHCPv6 server
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will be ignored. For details on how to enable the NTP client, see the
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[NTP Client Configuration](system.md#ntp-client-configuration) section.
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### Examples
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For advanced usage with vendor-specific options, see the YANG model.
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#### Use of DHCPv6 for IPv6 address assignment
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![Using DHCPv6 for IPv6 address assignment](img/ip-address-example-ipv6-dhcp.svg)
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admin@example:/> configure
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admin@example:/config/> edit interface eth0 ipv6
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admin@example:/config/interface/eth0/ipv6/> set dhcp
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admin@example:/config/interface/eth0/ipv6/> leave
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admin@example:/> show interface
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INTERFACE PROTOCOL STATE DATA
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eth0 ethernet UP 02:00:00:00:00:00
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ipv6 2001:db8::42/128 (dhcp)
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ipv6 fe80::ff:fe00:0/64 (link-layer)
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lo ethernet UP 00:00:00:00:00:00
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ipv4 127.0.0.1/8 (static)
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ipv6 ::1/128 (static)
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admin@example:/>
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The resulting address (2001:db8::42/128) is of type *dhcp*.
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To configure DHCPv6 client options, such as requesting prefix delegation
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for downstream networks, you can specify options:
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```
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admin@example:/> configure
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admin@example:/config/> edit interface eth0 ipv6 dhcp
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admin@example:/config/interface/eth0/ipv6/dhcp/> set option ia-pd
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admin@example:/config/interface/eth0/ipv6/dhcp/> set option dns-server
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admin@example:/config/interface/eth0/ipv6/dhcp/> show
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option dns-server;
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option ia-pd;
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admin@example:/config/interface/eth0/ipv6/dhcp/> leave
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admin@example:/>
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```
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For stateless DHCPv6 (used with SLAAC to get only configuration information):
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```
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admin@example:/> configure
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admin@example:/config/> edit interface eth0 ipv6 dhcp
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admin@example:/config/interface/eth0/ipv6/dhcp/> set information-only true
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admin@example:/config/interface/eth0/ipv6/dhcp/> show
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information-only true;
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option dns-server;
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option domain-search;
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admin@example:/config/interface/eth0/ipv6/dhcp/> leave
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admin@example:/>
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```
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Other useful DHCPv6 options include:
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- `duid` - Set a specific DHCPv6 Unique Identifier (auto-generated by default)
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- `client-fqdn` - Request the server to update DNS records with client's FQDN
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- `route-preference` - Set the administrative distance for DHCPv6-learned routes (default: 5)
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For advanced usage with vendor-specific options, see the YANG model.
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#### Disabling IPv6 link-local address(es)
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The (only) way to disable IPv6 link-local addresses is by disabling IPv6

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