Failure to bind socket when custom ip is set for ethernet adapter

Question

The problem

On our system running RTEMS 4.9.2 we are experiencing a very odd issue with socket communications. We are setting up a socket and using the following command to bind:

// Bind the socket to set the local port
sockaddr_in localSocketAddress = {0};
localSocketAddress.sin_family = AF_INET;
localSocketAddress.sin_port = (u_short)localPort;
localSocketAddress.sin_addr.s_addr = localAddress;

if (bind( mSocket, (sockaddr *)&localSocketAddress, sizeof(sockaddr_in)) == SOCKET_ERROR)
{
    int errorOut = errno;
    ...

And this works for UDP communications except in a strange specific scenario which is explained below. The problem that we experience is a failure of this bind call even though the setup is correct. We get the error 125 which for RTEMS is EADDRNOTAVAIL:

A nonexistent interface was requested or the requested address was not local.

The Apparent Cause

At boot of the device we can set up our network in 1 of 2 ways:

1. The Network IP and SUBNET is autoconfigured based on what is in the default bootloader (UBOOT), and is set up through the RTEMS OS.

2. The RTEMS function rtems_bsdnet_ifconfig is called to change the ip address of the sole ethernet interface after boot time.

For clarification, option 2 is called like this:

rtems_bsdnet_ifconfig(eth_interface, SIOCSIFADDR, &ipaddr);

If the network is set up as indicated by option 1, everything works as expected, but if option 2 is used (even in the case where the setup matches the network options defined by option 1) then the socket bind fails.

Is there a known reason or bug for RTEMS that indicates that this bind would fail if you reconfigure your IP?

Additional Information

• We are setting up a new IP address (option 2) using a method that essentially uses ioctl("eht1", SIOCSIFADDR, ...).

• If we bind our socket without specifying a local ADDRESS (ie use INADDR_ANY) then it works in any case.

• The rtems_bsdnet_ifconfig is a simple interface for the ioctl function. It is from rtems_glue.c and has the function signiture int rtems_bsdnet_ifconfig(const char *ifname, uint32_t cmd, void *param)

• All normal network functions seem to work except for this bind.

• After looking at this i thought maybe I needed to do more in resetting my IP address. But this doesn't work , using the first answer or even doing anything with SIOCSIFFLAGS causes all network functionality to cease.

Answer 1

You didn't mention the architecture you are running on, but you are setting the port and address in local byte order, which may not be the same as network byte order. The very first thing I would try is:

localSocketAddress.sin_port = htons (localPort); localSocketAddress.sin_addr.s_addr = htonl (localAddress);

This will also make your code more portable, in case that is NOT your problem (i.e. you are running on a big-endian host) and you one day try to compile on a different system that is little endian.