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Networking C++, don't see the packet in wireshark

Started by SonicD007 Jan 24, 2013 at 1:44 AM 4 replies 2.1k views

Original Post

Jan 24, 2013 at 1:44 AM

Hey everyone,

I'm messing around with sockets and I'm trying to send a simple packet using udp to a server. As of now, I'm just trying to see if the packet is being sent using wireshark. However, I don't see anything being sent. Is there anywhere I messed up here? (Aside from the system("PAUSE") and pretty much no error checking)

[source]

#include

#pragma comment(lib, "WS2_32.lib")

using namespace std;

int main(int argc, char* argv[])

{

WSADATA info;

WSAStartup(MAKEWORD(2,2), &info);

int client = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

if ( client < 0)

{

cout << "Error creating socket" << endl;

system("PAUSE");

return 1;

}

cout << "Socket created" << endl;

sockaddr_in clientinfo;

clientinfo.sin_family = AF_INET;

clientinfo.sin_addr.S_un.S_addr = inet_addr("127.0.0.1");

clientinfo.sin_port = htons(4511);

if (bind(client, (const sockaddr *)&clientinfo, sizeof(clientinfo))< 0)

{

cout << "Error binding socket" << endl;

system("PAUSE");

return 1;

}

cout << "Socket binded." << endl;

cout << "You may begin..." << endl;

string message = "";

sockaddr_in server;

server.sin_family = AF_INET;

server.sin_addr.S_un.S_addr = inet_addr("127.0.0.1");

server.sin_port = htons(4510);

while (message != "quit")

{

getline(cin, message);

if (message != "")

{

int i = sendto(client, message.c_str(), strlen(message.c_str() + 1), 0, (sockaddr *)&server, sizeof(server));

cout << "Packet Sent: " << i << " Bytes" << endl;

message = "";

}

return 0;

};

[/source]

Thanks.

EDIT: the format got messed up from the copy/paste

KulSeran

Jan 24, 2013 at 4:08 AM

You are probably hitting this issue: http://wiki.wireshark.org/CaptureSetup/Loopback

You aren't really sending any network traffic by hitting 127.0.0.1 since that is a special address. Thus by default nothing shows up during inspection.

violentrevolution

Jan 24, 2013 at 5:23 AM

Quite a few possibilities for not seeing packets getting transferred. Firstly check if you're not behind some VPN or anything.

95% of issues with wireshark not giving expected capture output is due to VPN, firewall, etc kind of troubles.

Then you need to check if there is some torrent network up on your machine. Torrent softwares tend to screw up Wireshark bigtime.

Actually, most of the issues with Wireshark not working, unless you're on Mac, are related to above 2 reasons.

And ofcourse, most popular reason is running capture on wrong network device. :-)

Bacterius

Jan 24, 2013 at 8:09 AM

You are probably hitting this issue: http://wiki.wireshark.org/CaptureSetup/Loopback

You aren't really sending any network traffic by hitting 127.0.0.1 since that is a special address. Thus by default nothing shows up during inspection.

Sending it to your local IP should be a workaround, though you might need to make a firewall exception. I've seen both cases happen, actually - the system trying to be helpful and resolving the local IP to localhost and nothing happening, as well as the packet bouncing off the router. Right now, for instance, my linux box resolves my local IP to ray.lan (my box), and my WAN (internet) IP to dsldevice.lan (the router), so in the former, the packets I send are going through the loopback interface, and in the latter, the router is just echoing back my pings.

If worst comes to worst, you can always create a virtual local network.

Khatharr

Jan 24, 2013 at 8:39 AM

I had the same problem on XP with both loopback and local IP. I haven't messed with it on Win7 yet. Loopback packets get handled without going all the way down the network stack, so wireshark doesn't get to see them. I eventually just looped through my router (cat5 to router, router to wifi card) so I could watch my traffic.

SonicD007

Jan 24, 2013 at 1:31 PM

Thanks everyone! I still don't see it in wireshark when I try sending it through my local IP but I'll give it another try using my WAN ip when I get up to NAT. On the bright side, my simple server is receiving the messages from my simple chat program

EDIT: I see the packet when sending outside my private network

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