curl_easy_perform failing when target is behind a NAT‏

HarryBoy · 11-10-2011, 06:47 AM

I am using curl in my c++ program to retrieve a url from a web server on two different linux machines.
Before I try to get the URL I try to connect to the server initially using the below code.

I have the following options set:

Code:

CURLcode tResult = CURLE_OK;
curl_easy_setopt ( pstdEasy, CURLOPT_HTTPHEADER, pstdTransferData->pstdHeaders  );
curl_easy_setopt ( pstdEasy, CURLOPT_HTTPGET, TRUE  );
curl_easy_setopt ( pstdEasy, CURLOPT_NOBODY, TRUE  );
curl_easy_setopt ( pstdEasy, CURLOPT_WRITEFUNCTION, OnReceiveHttpResponse  );
curl_easy_setopt ( pstdEasy, CURLOPT_WRITEDATA, pstdEasy  );

curl_easy_perform ( pstdEasy  );

the content of pstdTransferData->pstdHeaders is as follows:
User-Agent: MyDeviceName
Content-Type: text/xml
Expect:
Accept: text/xml, text/html, application/xml
Connection: Keep-Alive
Accept-Language: EN

I have two linux machines each with identical software and apache webserver the only difference is that one of them is behind a NAT with port forwarding set up.
Machine A has an address of 80.20.30.1
Machine B has an address of 192.168.200.1 which is behind a NAT with an address of 80.20.30.2.

The problem is that when I try to connect to Machine B (Which is behind the NAT) I get the response to be CURLE_GOT_NOTHING instead of CURLE_OK which is what I get when I connect to Machine A.

What could be wrong here? Why is the call failing when the target is behind a NAT.

If you need any more info just ask.

Thanks

Harry

stephen8 · 11-17-2011, 03:39 PM

Hi,

Can you capture tcp dump on both machines, open them with Wireshark and determinate if packet is reaching second box at all?
Have you managed to submit request manually using wget for example, and what was the result?
If you are able to submit successful request from the first box, also record tcp dump of that request.
Compare difference in those packets. If you are using iptables to setup your nat, can you post the output of the iptables --list