Gethostbyname() question

Mbed OS
1

Hi,
I’ve started with an UDP example on a NUCLEO_F746ZG and it worked fine from the beginning:

The IP address and gateway comes over dhcp and the gethostbyname(“time.nist.gov”) is working. Now I replace the address by a pc name in my LAN and I get an error -3009:

err = net.gethostbyname("sn-1.fritz.box", &sockAddr, NSAPI_IPv4);

finally, I got it only working by adding also the network name (which took also some time to figure it out):

err = net.gethostbyname("sn-1.fritz.box", &sockAddr, NSAPI_IPv4, "st0");

what is the reason for this? Also a

    net.set_as_default();

did not help. When I query the DNS, I get also my router IP as correct result.

2

I’ve done some more tests, it looks like the DNS for IPv6 is not set correct and the following gethostbyname does not work also:

with both IPv4 and IPv6 enabled in mbed_app.json:

IPv4 address is: 192.168.100.59
IPv6 local link is: fe80::280:e1ff:fe30:3a
gateway address is: 192.168.100.1
netmask is: 255.255.255.0
DNS IPv4: DNS 1: 192.168.100.1
DNS IPv4: DNS 2: 0.58.134.221

The DNS for index=0 is ok, the DNS for index=1 is not valid.

with only IPv6 enabled in mbed_app.json:

IPv4 address is: fe80::280:e1ff:fe30:3a
IPv6 local link is: fe80::280:e1ff:fe30:3a
get_gateway err: -3004
get_netmask err: -3004
DNS IPv6: DNS 1: 2001:4860:4860::8888
DNS IPv6: DNS 2: 80:e130:3a:86dd:6000:0:20:1

I get some ping reply from the first DNS, but on my pc the IPv6 DNS looks quite different:
fd00::464e:6dff:fe52:f02a
The second DNS looks like garbage, is not pingable.

Edit:
ok, the first DNS is a public google address and not my router.

int main() {
    printf("Hello from "  MBED_STRINGIFY(TARGET_NAME) "\n");
    printf("Mbed OS version: %d.%d.%d\n\n", MBED_MAJOR_VERSION, MBED_MINOR_VERSION, MBED_PATCH_VERSION); 

    SocketAddress sockAddr;
    volatile nsapi_error_t err;
    
    // Bring up the ethernet interface
    printf("UDP Socket example\n");
    if (0 != net.connect()) {
        printf("Error connecting\n");
        return -1;
    }

    // Show the network address
    net.get_ip_address(&sockAddr);
    printf("IPv4 address is: %s\n", sockAddr.get_ip_address() ? sockAddr.get_ip_address() : "No IP");
    net.get_ipv6_link_local_address(&sockAddr);
    printf("IPv6 local link is: %s\n", sockAddr.get_ip_address() ? sockAddr.get_ip_address() : "No IP");


    // get gateway
    err = net.get_gateway(&sockAddr);
    (err == NSAPI_ERROR_OK) ? printf("gateway address is: %s\n", sockAddr.get_ip_address()) : printf("get_gateway err: %d\n", err);

    // get netmask
    err = net.get_netmask(&sockAddr);
    (err == NSAPI_ERROR_OK) ? printf("netmask is: %s\n", sockAddr.get_ip_address()) : printf("get_netmask err: %d\n", err);

    int index = 0;
    while(err == NSAPI_ERROR_OK) {
        err = net.get_dns_server(index++, &sockAddr, "st0");
        switch (sockAddr.get_ip_version()) {
            case NSAPI_IPv4: printf("DNS IPv4: "); break;
            case NSAPI_IPv6: printf("DNS IPv6: "); break;
            default: printf ("DNS IPv unknown: ");
        }
        (err == NSAPI_ERROR_OK) ? printf("DNS %d: %s\n", index, sockAddr.get_ip_address()) : printf("get DNS err: %d\n", err);
    }

    UDPSocket sock;
    sock.open(&net);

    err = net.gethostbyname("sn-1.fritz.box", &sockAddr, NSAPI_IPv6, "st0");
    sockAddr.set_port(8888);
    (err == NSAPI_ERROR_OK) ? printf("remote address is: %s\n", sockAddr.get_ip_address()) : printf("gethostbyname err: %d\n", err);
}