Hi Jared, please see inline...

On 10-05-26 06:52 PM, Jared Roundy wrote:
> I have a UDP application that is started by inetd when a request on a
> specific socket it received.  I was testing various network
> occurrences and came across a problem when the Ip address was
> changed.  If the application is up and the IP address was changed I
> received UDP requests, but I could no longer transmit the replies.
> Are you aware of this problem?  Do you know of any fixes?

I'm not aware, but I'm probably not understanding your question 
correctly, please read on...

> I have found a work around that gets things working and I will
> describe it below.  I don't know why it works, and don't think it
> should be the final solution.
>
> I am running QNX 6.4.1 on a PC VM. To simulate the loss of a DHCP
> assigned IP address an acquisition of another I have turned off
> dhcp.client and am changing the IP address using ifconfig (ifconfig
> en0 inet<new IP>  netmask 255.255.255.0).

My first thought is that perhaps your app should be listening for 
address changes on a routing socket, but maybe that's unnecessarily 
complex, I don't know enough about your app...

> Here are the steps of my test.
> 1) Get the system running (network up, assigned iP address, etc).
> 2) Send a UDP request to my device and I get a response.

What kind of UDP request is this? To the stack, UDP is just UDP, there 
is no concept of requests. Is there anything special about it?

The code below hints at broadcasts are used, is that right? If so, what 
broadcast? Is the request and/or response broadcast? Is it using the 
limited broadcast (255.255.255.255) or the subnet directed broadcast 
(address | ~subnetmask)? Any other information I should know about it?

> 3) Change the Ip address using ifconfig command line.
> 4) Send the UDP request and sendto() fails the first time in the for loop returning a -1 with errno = 249.

This address indicates that the source address wasn't available. Did you 
bind the socket? To a unicast or broadcast address? If unicast, to the 
old interface address or the new? Or is your intent that you can send 
from and/or to a different address each time?

> 4a) If I send the request from the local network sendto() succeeds the second time.

What do you mean by "from the local network" here?

> 4b) If I send the request from a different subnet then sendto() fails the second time with errno = 251 and then 
succeeds the third time sendto() is called.
> NOTE: If I don't add the loop and set of the flag, then I
> continuously  get a sendto() error with errno = 249 on this socket until I change the
 > IP address back to the previously assigned one.

Depending on the situation the socket API requires you to 
SO_BINDTODEVICE in order for broadcasts to work.

> size_t UdpListenerConnection::Write(uint8_t const* dataBuffer, const size_t dataBufferSize, size_t writeTimeoutMs) //
lint --e{715}
> {
>     size_t numWritten = 0;
>
>     if (true == isOpen&&  NULL != dataBuffer&&  dataBufferSize>  0) {
>        socklen_t tolen = sizeof(fromAddress);
>        int errNum = 0;
>        struct sockaddr_in   broadcastAddress;
>        int flags = 0, i;
>
>        for (i=0;i<  3; i++) {
>           flags = 0;
>
>           memcpy(&broadcastAddress,&fromAddress, tolen);
>           if (249 == errNum) {
>              flags = MSG_DONTROUTE;
>           }
>
>           zError("Write: to=0x%x numBytes=%d", fromAddress.sin_addr.s_addr, dataBufferSize);
>           ssize_t writeReturn = sendto(mySocketHandle, dataBuffer, dataBufferSize, flags, (struct sockaddr*)&
broadcastAddress,  tolen);

This is a little confusing, zError() prints (or logs, I assume) the 
message that indicates you're writing to fromAddress, but then sendto() 
sends to...