Merge branch 'feature/lwip_ipv6_dhcp6' into 'master'

lw-ip: IPv6: Add support for DHCPv6 stateless config

Closes IDFGH-3249

See merge request espressif/esp-idf!14882

components/lwip/Kconfig

@@ -373,7 +373,7 @@ menu "LWIP"
 
     config LWIP_IPV6_RDNSS_MAX_DNS_SERVERS
         int "Use IPv6 Router Advertisement Recursive DNS Server Option"
-        depends on LWIP_IPV6
+        depends on LWIP_IPV6_AUTOCONFIG
         default 0
         help
             Use IPv6 Router Advertisement Recursive DNS Server Option (as per RFC 6106) to
@@ -381,6 +381,15 @@ menu "LWIP"
             Set this option to a number of desired DNS servers advertised in the RA protocol.
             This feature is disabled when set to 0.
 
+    config LWIP_IPV6_DHCP6
+        bool "Enable DHCPv6 stateless address autoconfiguration"
+        depends on LWIP_IPV6_AUTOCONFIG
+        default n
+        help
+            Enable DHCPv6 for IPv6 stateless address autoconfiguration.
+            Note that the dhcpv6 client has to be started using dhcp6_enable_stateless(netif);
+            Note that the stateful address autoconfiguration is not supported.
+
     config LWIP_NETIF_STATUS_CALLBACK
         bool "Enable status callback for network interfaces"
         default n

components/lwip/port/esp32/include/lwipopts.h

@@ -978,6 +978,8 @@
 
 #define LWIP_ND6_RDNSS_MAX_DNS_SERVERS  CONFIG_LWIP_IPV6_RDNSS_MAX_DNS_SERVERS
 
+#define LWIP_IPV6_DHCP6                 CONFIG_LWIP_IPV6_DHCP6
+
 /* Enable all Espressif-only options */
 
 #define ESP_LWIP                        1

docs/en/api-guides/lwip.rst

@@ -281,6 +281,58 @@ A number of configuration items are available to modify the task and the queues
 - :ref:`CONFIG_LWIP_TCPIP_TASK_STACK_SIZE`
 - :ref:`CONFIG_LWIP_TCPIP_TASK_AFFINITY`
 
+IPv6 Support
+------------
+
+Both IPv4 and IPv6 are supported as dual stack and enabled by default (IPv6 may be disabled if it's not needed, see :ref:`lwip-ram-usage`).
+IPv6 support is limited to *Stateless Autoconfiguration* only, *Stateful configuration* is not supported in ESP-IDF (not in upstream lwip).
+IPv6 Address configuration is defined by means of these protocols or services:
+
+- **SLAAC** IPv6 Stateless Address Autoconfiguration (RFC-2462)
+- **DHCPv6** Dynamic Host Configuration Protocol for IPv6 (RFC-8415)
+
+None of these two types of address configuration is enabled by default, so the device uses only Link Local addresses or statically defined addresses.
+
+.. _lwip-ivp6-autoconfig:
+
+Stateless Autoconfiguration Process
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+To enable address autoconfiguration using Router Advertisement protocol please enable:
+
+- :ref:`CONFIG_LWIP_IPV6_AUTOCONFIG`
+
+This configuration option enables IPv6 autoconfiguration for all network interfaces
+(in contrast to the upstream lwIP, where the autoconfiguration needs to be explicitly enabled for each netif with ``netif->ip6_autoconfig_enabled=1``
+
+.. _lwip-ivp6-dhcp6:
+
+DHCPv6
+^^^^^^
+
+DHCPv6 in lwIP is very simple and support only stateless configuration. It could be enabled using:
+
+- :ref:`CONFIG_LWIP_IPV6_DHCP6`
+
+Since the DHCPv6 works only in its stateless configuration, the :ref:`lwip-ivp6-autoconfig` has to be enabled, too, by means of :ref:`CONFIG_LWIP_IPV6_AUTOCONFIG`.
+Moreover, the DHCPv6 needs to be explicitly enabled form the application code using
+
+    dhcp6_enable_stateless(netif);
+
+DNS servers in IPv6 autoconfiguration
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+In order to autoconfigure DNS server(s), especially in IPv6 only networks, we have these two options
+
+- Recursive domain name system -- this belongs to the Neighbor Discovery Protocol (NDP), uses :ref:`lwip-ivp6-autoconfig`.
+  Number of servers must be set :ref:`CONFIG_LWIP_IPV6_RDNSS_MAX_DNS_SERVERS`, this is option is disabled (set to 0) by default.
+
+- DHCPv6 stateless configuration -- uses :ref:`lwip-ivp6-dhcp6` to configure DNS servers. Note that the this configuration
+  assumes IPv6 Router Advertisement Flags (RFC-5175) to be set to
+
+    - Managed Address Configuration Flag = 0
+    - Other Configuration Flag = 1
+
 esp-lwip custom modifications
 -----------------------------