VirtualBox network connectivity broken on recent -CURRENT

[Don Lewis]

On  4 Jun, Alan Somers wrote:
> On Fri, Jun 3, 2016 at 6:43 PM, Don Lewis <truckman at freebsd.org> wrote:
>> On  3 Jun, Don Lewis wrote:
>>> It looks like something changed in -CURRENT to break network
>>> connectivity to VirtualBox guests.  This was last known to work with
>>> r299139 (May 6th) and is definitely broken with r301229.  The VirtualBox
>>> port revisions are:
>>>       virtualbox-ose-4.3.38_1
>>>       virtualbox-ose-kmod-4.3.38
>>> It looks like there was one change to the VirtualBox on May 9th, but it
>>> looks unlikely to be the cause of the problem.
>>>
>>> The network settings are:
>>>       Attached to: Bridged Adapter
>>>       Name: re0
>>>       Adapter Type: Paravirtualized Network (virtio-net)
>>>       Promiscuous Mode: Deny
>>>       MAC Address: [snip]
>>> Ifconfig says that the interface is up, but I am unable to ping either
>>> the host or anything else on the LAN from the guest.  It looks like the
>>> problem is with outbound traffic.  If I attempt to ping the guest, the
>>> source IP address and MAC address show up in the guest's arp table, but
>>> ping reports:
>>>       ping: sendto: Host is down
>>> That makes me think that the arp responses from the guest are not
>>> getting transmitted.  None of the machines involved are running
>>> firewalls.  If I ping from the guest, I don't see any arp requests on
>>> the wire and the arp command shows the table entry as incomplete.
>>>
>>> The problem shows up with both FreeBSD -CURRENT and Debian guests.
>>
>> I see the same behaviour if I set:
>>         Attached to: NAT
>> or
>>         Adapter Type: 82540EM
>>
> 
> Might be related to this routing bug:
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=207831

Doesn't look like it.  The questionable commit there seems to be
r293159.  I didn't see breakage until after r299139.