"David Goodenough" <nobody@nowhere.xyz> wrote:

> I'm planning on setting up ethernet bridging on a Windows XP system,
> in order to get a connection with OpenVPN working. From what I
> understand, when I bridge the two ethernet adapters in XP (*), it
> makes some sort of announcement that the bridge has been set up.
>
> (*) One being the physical NIC, the other the "virtual" OpenVPN NIC.
>
> What is the nature of this announcement? Is there an RFC that covers
> the details? Is it routable, or does it only go as far as the local
> subnets attached to the two interfaces?

If you're really bridging, and not routing, then in principle there's no
need for any announcement. A new host connecting via an Ethernet bridged
through the Windows machine would go about its business the usual way,
e.g. beginning with a DHCP broadcast request, and the bridge sends on
the broadcast to the VPN side. And the reply would come back the same
way, because the switches between the new host and the router will have
learned the way back.

If the Windows machine is running STP or RSTP, then Bridge Protocol Data
Unit (BPDU) frames are exchanged between this switch and other switches
in the catenet, as described in IEEE 802.1D, which you can download for
free from the IEEE web site.

Bert