[DRBD-user] Using DRBD between hosts with dual redundant network interfaces

paddy paddy at panici.net
Wed Jul 6 14:23:40 CEST 2005

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Tue, Jul 05, 2005 at 05:38:51PM -0400, Ward Horner wrote:
> Here's the scenario I am trying to solve:
> I have two computers each with two network interfaces. Both network 
> interfaces are on different networks and use different switches. Neither 
> network can communicate with the other. This is a typical dual redundant 
> network  topology.
> I want to setup drbd to be able to use BOTH networks. If a network fails, 
> it would be disabled, however communications would continue on the other 
> network.
> For example:
> --> On the primary host, eth0 is set to and eth1 is set to 
> eth0 and eth1 are on different subnets and different physical 
> networks.
> --> On the secondary host, eth0 is and eth1 is
> --> Both eth0's can communicate and both eth1's can communicate, but eth0 
> and eth1 on different hosts cannot.
> --> I want to set up drbd to be able to use both eth0 and eth1 for 
> communication. On each host, all info that goes to eth0 should also be sent 
> to eth1.
> --> drbd services on the each host should be able to receive duplicate 
> communication over both eth0 and eth1 and not get confused.
> I realize this is a difficult scenario and drbd probably does not handle 
> this type of configuration. This is, however, a very common redundant 
> network setup. So I was wondering if there is a way to setup drbd to 
> operate in this type redundant network. Does anyone know if this is 
> possible? Does anyone have any thoughts or ideas on this issue?

Hmmm, deja vu ?

Ok, my second effort ...

what's wrong with a simple ipip tunnel like so

at primary:

modprobe ipip
ifconfig tunl0 up
route add gw

at secondary:
ifconfig tunl0 up
route add gw

run some sort of heartbeat over your two network connections and fail
you route back and forth as applicable. left as an exercise ;)

I haven't tried this, as I don't have that kind of setup handy, but
everyone's allowed to drop the occasional packet aren't they ?

(I would have done it without the tunnelling, but this way was quick
to find and a bit more general.  I'm sure there's a way to do closer 
to what you ask for out there somewhere. worst come to worst, it 
doesn't sound especially hard to roll up yourself :)

As you say, I don't imagine (ok, I don't know:) that drbd handles 
this kind of setup directly, but I don't understand what you win
by exposing this kind of detail to drbd.  

	Why not just have one virtual device with an ip address 
	for drbd to connect to and deal with the rest behind it's back?

Also, I think there may be various channel bonding options that
might look a bit like what you ask for.

Good Luck, and let us know what you find !

Perl 6 will give you the big knob. -- Larry Wall

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