OpenVPN Support Forum

In openVPN, we learn that routing does not transmit non-IP protocols like broadcast, IPX. The advantage of bridging is that it does transmit those protocols. But I am confused that why the routers we buy at out local computer store, which should follow the routing mode, can transmit non-IP protocols? Aren't they suppose to act like openVPN that it just ignores those packets? What's the reason?


Thanks.

This is a common misconception , largely caused by the names used : "routing" vs "bridging".

A tun-style setup (--dev tun) is often referred to as a routed setup. Tun adapters can forward only IP based traffic, by design.

OpenVPN also supports a tap-style setup (--dev tap) without resorting to bridging. In this case, full Ethernet frames are forward via the tunnel, so you can forward IPX/AppleTalk/whatever type of traffic over such a link. Your typical home router resembles this.

Bridging mode is a special case of a tap-style setup where the tap adapter and a local ethernet adapter (or another tap-adapter, for that matter) are bridged to form a single adapter. All traffic coming in on one interface is automatically re-broadcasted on the other interface(s). This can be handy to bridge two networks together (like a virtual hub) but it does have a serious impact on performance and scalability.

PS there's no need to thank me for doing your homework

hmm..., that's interesting

so the home "routers" we buy are actually doing the bridging, not the routing, that's kind of confusing. I should probably say our home routers are routing + bridging

hi cpthk,

just curious...

what router are you using?


michael.

some home routers do routing+bridging, mostly when buying a wireless router.
Most home routers don't do bridging, but they do routing+switching:
- all traffic which is forwarded out the WAN port (to your cable/DSL provider) is routed; it is, generally speaking, quite hard to route IPX traffic via your provider.
- your local PCs which are all connected via wires to the router form a single subnet, so the router acts as a switch here.

As I said, some home routers make the wired and wireless networks appear as one, which is usually done using bridging.