Hello,

It's entirely possible that I'm going about this all the wrong way... I'm new 
here. :-)

I'm trying to set up an environment that works a bit like a private LAN within 
Amazon's EC2 cloud. EC2 allows me to provision a bunch of servers on demand, 
but they don't have predictable internal IP addresses for communicating with 
one another, which makes things a little complicated.

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.

The topology I've been experimenting with for now is one where I have a 
"master" server, a "slave" server, and many "client" servers. I'd like the 
"master" and "slave" servers to have static IPs, and the "client" servers to 
get their addresses via DHCP. I have it so that the master and slave have a tap 
tunnel between them, and every client has a tap tunnel to both the master and 
the slave (but not to the other clients). Each client should be able to ping 
both the master and slave. I don't care if they can ping the other clients or 
not.

I've got it set up so that the master and slave each have a bridge interface 
that aggregates all of the tunnels from each client (and the one to each 
other). Each client has a bridge interface that aggregates the two tunnels to 
the master and slave. All are called br0.

I'm not adding any eth interfaces to the bridge, just the tap interfaces.

I'm running a DHCP server on the master and slave in failover mode and 
listening on br0, and on each client I'm attempting to obtain an IP address for 
the br0 interface using a DHCP client.

I have stp switched on everywhere. If I disable stp all hell breaks loose and I 
get duplicate packets all over the place.

I basically want each server to appear to have one interface, despite the fact 
that there are multiple tunnels. I also want the system to work if either the 
master or the slave server goes away.

What I was hoping would happen is that packets would take the shortest route to 
where they want to go. They should only ever have to go over one tunnel, except 
for clients attempting to contact each other (this never happens) or broadcast 
packets (which only really need to go to the master/slave for DHCP anyway)

In practice, it seems that packets sent from a client server to a master or 
slave are always going over the same tap interface, even if it is not the 
shortest route. (Pings sent to both the master and slave are going out over 
tap0, all that I can see on tap1 is stp traffic).

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.

What am I missing?

Thanks,
Simon

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