Network tracing

The network problem usually could be detected by log, but pcap files might talks more then other sources of information because it contains information about all packets received/send by guest. To enable network tracing do the following

# VBoxManage modify [your-vm] -nictrace[adapter-number] on -nicatracefile[adapter-number] file.pcap
# VirtualBox -startvm [your-vm]

e.g.

# VBoxManage modify "ubuntu" -nictrace1 on -nicatracefile1 file.pcap
# VirtualBox -startvm "ubuntu"

Note: Don't forget to switch tracing of because your hdd will be eaten by pcap files in case of intensive network usage. The port-forwarding configuration might be affected by this setting also.