Dual hosting Ethernet+WiFi, get IP address(es) programatically

Question

Using azsphere device wifi show-status I can easily determine the WiFi IP address of the device. Can I do the same for the ethernet interface from the command line? This is useful to do if the address is allocated by an external DHCP e.g. on a router.

I have modified EchoServer_Start in the PrivateNetworkServices sample as follows

    struct sockaddr_in bound;
    size_t szBound = sizeof(bound);
    getsockname(serverState->listenFd, &bound, &szBound);

    Log_Debug("INFO: TCP server: Listening for client connection (fd %d) on %s\n",
              serverState->listenFd, inet_ntoa(bound.sin_addr));

and it duly prints out an expected IP address.

However when the device is multi-homed with both eth0 and wlan0 I do not seem to be able to chose which interface to run the TCP server on.

The output from the app with static const char NetworkInterface[] = "eth0"; is as below (192.168.178.70 is the device's Ethernet IP address).

INFO: Networking_GetInterfaceCount: count=2
INFO: Networking_GetInterfaces: actualCount=2
INFO: interface #0
INFO: interfaceName="eth0"
INFO: isEnabled="1"
INFO: ipConfigurationType=1 (DhcpClient)
INFO: interfaceMediumType=2 (Ethernet)
INFO: interfaceStatus=0x0f
INFO: interface #1
INFO: interfaceName="wlan0"
INFO: isEnabled="1"
INFO: ipConfigurationType=1 (DhcpClient)
INFO: interfaceMediumType=1 (Wi-Fi)
INFO: interfaceStatus=0x0f
INFO: SNTP server has started on network interface: eth0.
INFO: TCP server: Listening for client connection (fd 8) on 192.168.178.70

The output from the app with static const char NetworkInterface[] = "wlan0"; is as below

INFO: Networking_GetInterfaceCount: count=2
INFO: Networking_GetInterfaces: actualCount=2
INFO: interface #0
INFO: interfaceName="eth0"
INFO: isEnabled="1"
INFO: ipConfigurationType=1 (DhcpClient)
INFO: interfaceMediumType=2 (Ethernet)
INFO: interfaceStatus=0x0f
INFO: interface #1
INFO: interfaceName="wlan0"
INFO: isEnabled="1"
INFO: ipConfigurationType=1 (DhcpClient)
INFO: interfaceMediumType=1 (Wi-Fi)
INFO: interfaceStatus=0x0f
INFO: SNTP server has started on network interface: wlan0.
INFO: TCP server: Listening for client connection (fd 8) on 192.168.178.70

I have tried adding to OpenIpV4Socket after the existing setsockopt, as below

        char *devname = "wlan0";
        r = setsockopt(localFd, SOL_SOCKET, SO_BINDTODEVICE, devname, strlen(devname));
        if (r != 0) {
            Log_Debug("INFO: TCP server: setsockopt failed with %d\n", errno);
        }

but this always fails. It seems odd that Networking_SntpServer_Start can accept an interface but we do not seem to have a way for specifying an interface for a TCP server (or generic socket).

Is there a reason for this restriction or have I done something wrong or missed something?

Thanks.

Answer 1

@bill chadwick Below is the response received from our product group on your queries.

Q: Why is there no way to determine the Ethernet IP address from the command line tool?

A: This is a good design change request, thank you for the feedback.

Update:
Q: It seems odd that Networking_SntpServer_Start can accept an interface but we do not seem to have a way for specifying an interface for a TCP server (or generic socket). Is there a reason for this restriction or have I done something wrong or missed something? ... Why does setsockopt to specify an interface not work? (especially when the NTP server can be started on a nominated interface)

A: You cannot use SO_BINDTODEVICE due to security issues with allowing CAP_NET_ADMIN or CAP_NET_RAW. Instead you can query for the IP via getifadddr and bind to this IP on the interface of choice as show in https://github.com/Azure/azure-sphere-samples/blob/b26a88e8ee2fba679f4d28a3184b4d0c95ad5547/Samples/PrivateNetworkServices/echo_tcp_server.c

Q: Can you please also suggest a way that the IP address of both interfaces might easily be determined programmatically

A: getifaddrs()

Please let us know if you have any further queries.

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