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net: dhcpv4: Honor network interface for DNS servers

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Bind the network interface to the network interface we
have received the DNS servers from. This is now the default.
The previous behavior can be restored by disabling the
CONFIG_NET_DHCPV4_DNS_SERVER_VIA_INTERFACE option.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>
This commit is contained in:
Jukka Rissanen 2025-06-11 13:47:23 +03:00 • committed by Henrik Brix Andersen
commit 1224c5a43a
2 changed files with 36 additions and 1 deletions
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17
subsys/net/lib/dhcpv4/Kconfig
View file

@ -96,6 +96,23 @@ config NET_DHCPV4_OPTION_PRINT_IGNORED
received and ignored. If this is not set, then we print these as unknown
options.
config NET_DHCPV4_DNS_SERVER_VIA_INTERFACE
bool "Make DNS servers specific to the network interface"
depends on NET_DHCPV4_OPTION_DNS_ADDRESS
default y
help
If this is set, then if the system has multiple network interfaces
and each has DHCP enabled, then assign DNS servers received from that
network interface, to that specific interface.
If this option is not set, then any interface can be used for all
the configured DNS server addresses when doing DNS queries.
Example: We receive DNS server 192.0.2.53 DHCPv4 option from Wi-Fi
interface and DNS server 198.51.100.53 from Ethernet interface.
When this option is set, the DNS resolver will use DNS server
192.0.2.53 when sending DNS query to the Wi-Fi interface and DNS
server 198.51.100.53 when sending DNS query to the Ethernet
interface.
endif # NET_DHCPV4
config NET_DHCPV4_SERVER

20
subsys/net/lib/dhcpv4/dhcpv4.c
View file

@ -1171,7 +1171,25 @@ static bool dhcpv4_parse_options(struct net_pkt *pkt,
for (uint8_t i = 0; i < dns_servers_cnt; i++) {
dnses[i].sin_family = AF_INET;
}
status = dns_resolve_reconfigure(ctx, NULL, dns_servers);
if (IS_ENABLED(CONFIG_NET_DHCPV4_DNS_SERVER_VIA_INTERFACE)) {
/* If we are using the interface to resolve DNS servers,
* we need to save the interface index.
*/
int ifindex = net_if_get_by_iface(iface);
int interfaces[MAX_DNS_SERVERS];
for (uint8_t i = 0; i < dns_servers_cnt; i++) {
interfaces[i] = ifindex;
}
status = dns_resolve_reconfigure_with_interfaces(ctx, NULL,
dns_servers,
interfaces);
} else {
status = dns_resolve_reconfigure(ctx, NULL, dns_servers);
}
if (status < 0) {
NET_DBG("options_dns, failed to set "
"resolve address: %d", status);