mcx(4) and bridge(4)

[Hauke Fath <hf%spg.tu-darmstadt.de@localhost>]

Hi,

I am not really sure where to take this, port-xen or tech-net -- picture 
the following setup:

A netbsd-10 xen Dom0 hangs off a mcx(4) interface, with three vlans 
(2,3,5) hooked onto three bridge(4)s. The vlans are for the sake of the 
DomUs, the Dom0 itself has an ip on vlan2.

There is right now one PV DomU which is a dump | restore copy of an 
existing netbsd-9 installation from another Dom0. It also has an ip on 
vlan2 via the usual xen procedure; vlans 3 + 5 are currently unused.

The setup mimics that of two Dom0 machines with different (older) 
hardware and OS.

The Dom0 has full network access without any issues.

The DomU can reach the Dom0 and vice versa (ssh login). But nothing it 
sends will leave the Dom0; a tcpdump on vlan2 logs its arp requests for 
external addresses (default gateway, subnet-local nameserver), but never 
a reply.

It isn't the switch: I tried connecting the second mcx interface to a 
different switch, no change.

Using an onboard bge(4) nic instead of the mcx(4), the DomU has fully 
functional network access. That would be fine for now, but the planned 
use of the mmachine will need the mcx(4)'s bandwidth.

Does this speak to anybody? Where should I start looking? I guess, it's 
a PR...

Cheerio,
Hauke

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