VirtualBox network connectivity broken on recent -CURRENT

[Alan Somers]

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