espressif: ipv6: Disable RDNSS #9713
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Recursive DNS Server (RDNSS) is an extension of IPv6 Neighbor Discovery. It is one of several ways (in addition to DHCPv6) to inform a network node of a usable DNS server. In LWIP, it appears any RDNSS DNS server will overwrite a DNS server from DHCPv4 or manual configuration, whether or not CircuitPython has an IPv6 address configured. In the (default) case where DHCPv6 is disabled in CircuitPython, but the (apparently rare) case where a RDNSS advertisement is broadast, this means that DNS doesn't work, and it appears that assigning to the dns or ipv4_dns properties of the Radio object doesn't work (when in reality it's frequently being reset to the value from RDNSS) On my network, the same DNS server is advertised by DHCPv6, so with this change I still get a working v6 configuration with a v6 DNS server when I enable DHCPv6, but when configuring as v4 only (the default), the correct IPv4 DNS server setting happens and I can also manually change it by assigning .dns or .ipv4_dns.
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Just based on some grepping around it looks like micropython takes the default value of 0 for CONFIG_LWIP_IPV6_RDNSS_MAX_DNS_SERVERS which if correct makes me feel better about taking this change. |
tannewt
approved these changes
Oct 15, 2024
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Recursive DNS Server (RDNSS) is an extension of IPv6 Neighbor Discovery. It is one of several ways (in addition to DHCPv6) to inform a network node of a usable DNS server.
In LWIP, it appears any RDNSS DNS server will overwrite a DNS server from DHCPv4 or manual configuration, whether or not CircuitPython has an IPv6 address configured.
In the (default) case where DHCPv6 is disabled in CircuitPython, but the (apparently rare) case where a RDNSS advertisement is broadast, this means that DNS doesn't work, and it appears that assigning to the dns or ipv4_dns properties of the Radio object doesn't work (when in reality it's frequently being reset to the value from RDNSS)
On my network, the same DNS server is advertised by DHCPv6, so with this change I still get a working v6 configuration with a v6 DNS server when I enable DHCPv6, but when configuring as v4 only (the default), the correct IPv4 DNS server setting happens and I can also manually change it by assigning .dns or .ipv4_dns.
Closes: #9712