2

I would like to ask about the relation between 802.11 and Ethernet L2 Link layer. Are they dependent of each other? Or can they be seen as independent L2 link layers (with only similarities in their headers)?

When capturing packets in Linux in non-monitor mode on a interface the packets will be displayed as "fake" ethernet frames. In monitor mode the "real" frames look quite different. This is quite confusing. My guessing is that the two link layers are actually totally independent.

In particular I wonder how a packet that comes in on a ethernet interface and goes out on a 802.11 interface transforms when the host is configured as a linux router: For instance is there a one-one mapping between the ethernet 802.1Q vlan tags? Or are there even automatic encapsulation mechanisms in the standard (and therefore the two link layers being coupled to each other) ... etc.

Is the relation of 802.11ad (60Ghz) to ethernet similar as that of the other 802.11 standard to ethernet? // Greetings Konrad

5

Ethernet (IEEE 802.3) and Wi-Fi (IEEE 802.11) are two completely separate layer-1/2 protocols, with different layer-2 frames. Each IEEE LAN type (ethernet, token-ring, FDDI, Wi-Fi, etc.) has it own frame format.

Since the packets are encapsulated by the frames, the packets can easily be transferred from one LAN type to another by discarding and building new frames. Routers do this as a matter of course; every frame coming into a router is stripped and discarded, the packet is switched to a new interface, and a new frame is built for the new interface.

With bridges, it is a little different. A bridge that has multiple LAN types needs to be a translating bridge to translate between the different frame types. Unlike transparent bridges, e.g. ethernet switches, translating bridges must strip the frames, but the frame information may need to be preserved in order to build a new new frame for the new LAN type. For instance, ethernet/token-ring bridges need to change the MAC addresses to/from ethernet and token-ring's canonical format. A WAP is really just a translating bridge.

Wi-Fi doesn't really have VLANs the way ethernet does. Normally, VLANs translate to SSIDs. There is/was a proposed standard to add VLANs to point-to-point Wi-Fi links in order to trunk wirelessly between two ethernet switches, but I have never seen it implemented, and I don't think there is much support for it.

802.11ad is just another Wi-Fi standard, the way ethernet has many different standards, e.g. 802.3z (gigabit ethernet).

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.