NOTE: In capture methods involving emulators, you should configure your computer to disable offloading.
Fire up DeSmuME and Wireshark.
Start recording in Wireshark.
Play online and capture some packets!
When you're done playing stop the capture and look for the IP address DeSmuME was using. Type "
bootp" into the filter text box and hit enter. Find the entry labeled "DHCP ACK - Transaction ID ..." and look at the Destination field on that packet. That is the IP DeSmuME was using. (NOTE: This can change from session to session so this step has to be repeated every time.)
In the filter text box, clear the text in there and input "
ip.addr == <DEVICE_IP>" instead and apply it, where "
<DEVICE_IP>" is the IP address you found in the previous step. These are the packets you want to save.
To export your capture, go to File -> Export Specified Packets and in the save dialog, make sure the packet range is set to Displayed.