[Bridge] Bridging without forwarding? (not bonding)

Simon Detheridge simon at widgit.com
Mon Jan 5 15:35:20 PST 2009

I wrote:
> What I'm trying to do is use a combination of vtun tap tunnels and
> bridging, to make my servers feel like they're on a LAN together.

... snip ...

> Really what I want to do is forget about stp and just have each
> bridge interface send out packets over the correct tap interface based
> on what mac address is at the other end, but not bother to forward
> anything on, as it should never be necessary.

"Ross Vandegrift" <ross at kallisti.us> wrote:
> Based on your description, what you really want is broadcast GRE.
> Check out http://linux-ip.net/gl/ip-tunnels/node9.html for a basic
> description.

Unfortunately, Amazon will only route tcp/udp. Other protocols don't work, and as such it's not even possible to set up an ipsec-based VPN... VTun and OpenVPN seem to be the only solutions.

richardvoigt at gmail.com wrote:
> Leave the master-slave server tunnel separate from the bridges?  That
> connection is different from the others anyway, and making it
> independent of the bridges will break the loop.

That doesn't work. I set up a standard ptp tunnel between the master/slave, leaving the bridges just for the connections to the clients. When connecting a bunch of clients, I still wind up with a box that routes all packets over one tunnel. showstp tells me that one tunnel is blocked and the other is forwarding. Suprising. I thought stp would find the shortest route, but this takes three hops as packets can go client->master->different client->slave.

> Alternatively, you could use ebtables to drop all packets in the
> FORWARD chain.

Bingo. Switching off stp on all nodes, and saying "ebtables -P FORWARD DROP" makes everything work exactly how I want. I hadn't found ebtables until now. :-)

Thanks for the help... :-)

Simon Detheridge - CTO, Widgit Software
26 Queen Street, Cubbington, CV32 7NA - Tel: +44 (0)1926 333680

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