Pushing a certain quantity/mixture of data through a VB guest's NAT interface causes all TCP/UDP connections to fail for a period of time thereafter.
The only way I've been able to reliably reproduce this is to use pip(1)
to download a large list of Python packages. After a number of packages have been downloaded (14~20) pip will exit with an HTTP or DNS timeout. Inbound port-forwarded SSH connections will drop with:
Connection to 127.0.0.1 closed by remote host.
This appears most likely to occur with the Intel PRO/1000 MT Desktop (82540EM)
NIC. It is harder to reproduce with PCnet-FAST III (Am79C973)
NICs. It is not reproducible with host-only or bridged adapters.