OpenVPN and L2-loop

roaldmortsell

Hi,

we are setting up 2 routers Router A and Router B, each with their individual OpenVPN-tunnel to Router C. The intention is to extend the L2-Broadcast domain behind Router A and B to the Router C. Router A and B bridge their LAN-ports to the OpenVPN tunnel forcing all traffic over the tunnel towards Router C and Router C's LAN-port.

Network X------------Router A----------OpenVPN------------Router C-------------Network X
| |
| |
Network X------------Router B----------OpenVPN------------

Now, in Network X behind router A is attached a unit that communicates with another unit attached to Router B. They essentially extend the same L2-broadcast (network X) domain to each other over a Wifi-network.

My question is simple...does this create a Logical L2 Loop between Router A, B and C, thus risking a broadcast storm?

Any answer is highly appreciated

Thanks!

Traffic

roaldmortsell wrotedoes this create a Logical L2 Loop between Router A, B and C, thus risking a broadcast storm?

Probably not ..

Think of OSI Layer-2 as a physical extension to the LAN cable .. thus your diagram would be more like so :

Network:X = 192.168.71.0/24:

192.168.71.101-149/24---Router A---OpenVPN---\
                                              \
                                               Router C------------192.168.71.1-99/24
                                              /
192.168.71.151-199/24---Router B---OpenVPN---/

But bare in mind .. this will put a lot of extra (broadcast etc) packets on the entire wire (not just openvpn) ..

roaldmortsell

You are right about your view of OSI L2 and physical...but it seems you missed the important part of the 2 units behind router A and B that transports the same BC-domain over Wifi between eachother, and together with openvpn creates a L2-loop...that is the key to answering my question.

I am not very familiar with Openvpn but could it be it employs some type of mechanism like poison-reverse does for L3 with regards to avoiding a broadcast storm? I'm just thinking way wide here

Traffic

roaldmortsell wroteit seems you missed the important part of the 2 units behind router A and B that transports the same BC-domain over Wifi between eachother

roaldmortsell wroteThey essentially extend the same L2-broadcast (network X) domain to each other over a Wifi-network

Ah-ha .. yes indeed ..

roaldmortsell wroteI am not very familiar with Openvpn but could it be it employs some type of mechanism like poison-reverse does for L3 with regards to avoiding a broadcast storm?

Not to my knowledge .. but a dev may have a definitive answer. (Try the mailing list)

jameshouston135

very informative for me.