CTL_NET_IPv4_ADDR_t ctl_dns_primary_server_addr(void);
ctl_dns_primary_server_addr returns the primary DNS server as set in the CTL_IP_CONFIG_t passed to ctl_net_init or or retrieved from a DHCP server.
If IP addresses are assigned by DHCP, ctl_dns_primary_server_addr will returns an all-zero IP address whilst IP negotiation is in progress.