Re: vlans and netbsd-current

[Darren Reed <darrenr%netbsd.org@localhost>]

On 9/06/2014 3:01 AM, Thor Lancelot Simon wrote:
> On Mon, Jun 09, 2014 at 02:45:19AM +1000, Darren Reed wrote:
>>> In Sun, Jun 08, 2014 at 10:56:50PM +1000, Darren Reed wrote:
>>>>
>>> ...
>>>>         inet6 fe80::203:baff:fe34:a1f5%cas0 prefixlen 64 scopeid 0x6
>>>> vlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>>>>         vlan: 200 parent: cas0
>>>>         address: 00:03:ba:34:a1:f5
>>>> ...
>>>> vlan1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>>>>         vlan: 201 parent: cas0
>>>>         address: 00:03:ba:34:a1:f5
>>>
>>>> I've got three interfaces with the same MAC address!
>>>
>>> This is correct.  It is an error to connect two vlan interfaces on the
>>> same underlying physical network to the same layer 2 network.  So the
>>> MAC address being the same can't cause problems.
>>> ...
>>> Note that the
>>> pathological case where you configure two vlan interfaces on the same
>>> physical interface with the _same_ vlanif, simulating dual-attach to the
>>> same physical LAN in the SunOS 4 case (which is where that was problematic)
>>> is also insane -- it's easy enough to work out why.
>>
>> I think you're wrong here.
>>
>> For example, what if I were to create two chroot environments on my
>> NetBSD box and I wanted to use a dedicated NIC and IP address for each?
>> And if I want each NIC to be its own vlan interface?
>>
>> Or what if I want to do virtual networking inside of NetBSD and create
>> a vwire between two vlan interfaces?
>>
>> Or connect both vlan interfaces to a virtual switch inside the kernel?
> 
> Why do any of these require stacking two instances of vlan, with the same
> vlanif, on the same physical interface?

In the first instance, because NetBSD vlan interfaces that have a vlanid
cannot exist without a hardware interface underneath them. So if you only
have one NIC, say bge0, then every vlan interface must have that under it.

To put this another way, if I can plug bge0 and bge1 into the same LAN
and use them in whichever way, why can't I plug vlan0 and vlan1 both
into the same VLAN?

Darren