net: ipv6: Add support for default gateway discovery.

In IPv6, the default gateway and prefix length are determined by receiving
a router advertisement as defined in -
https://www.rfc-editor.org/rfc/rfc4861.

Add support for sending router solicitation (RS) and processing router
advertisements (RA).

If the RA has prefix info option and following conditions are met, then
gatewayip6 and net_prefix_length of ip6addr env variables are initialized.
These are later consumed by IPv6 code for non-local destination IP.

- "Router Lifetime" != 0
- Prefix is NOT link-local prefix (0xfe80::/10)
- L flag is 1
- "Valid Lifetime" != 0

Timing Parameters:
- MAX_RTR_SOLICITATION_DELAY (0-1s)
- RTR_SOLICITATION_INTERVAL (4s) (min retransmit delay)
- MAX_RTR_SOLICITATIONS (3 RS transmissions)

The functionality is enabled by CONFIG_IPV6_ROUTER_DISCOVERY and invoked
automatically from net_init_loop().

Signed-off-by: Ehsan Mohandesi <[email protected]>
Tested-by: Viacheslav Mitrofanov <[email protected]>Reviewed-by:
Tested-by: Viacheslav Mitrofanov <[email protected]>
Reviewed-by: Viacheslav Mitrofanov <[email protected]>
Tested-by: Sergei Antonov <[email protected]>
Reviewed-by: Sergei Antonov <[email protected]>

1 files changed, 6 insertions, 0 deletions

diff --git a/cmd/Kconfig b/cmd/Kconfig
index 460f29883ae..65957da7f57 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1942,6 +1942,12 @@ config CMD_NCSI
 	  Normally this happens automatically before other network
 	  operations.
 
+config IPV6_ROUTER_DISCOVERY
+	bool "Do IPv6 router discovery"
+	depends on IPV6
+	help
+	  Will automatically perform router solicitation on first IPv6
+	  network operation
 endif
 
 config CMD_ETHSW