Say there are 2 computers are connected this way in a wireless network:

Computer A -> Access Point 1 -> Access Point 2 -> Computer B

When a frame is sent from Computer A to Computer B, the frame needs to be first sent to Access Point 1 then Access Point 2 then eventually Computer B.

3 frames are generated along the way. In its 802.11 frame, the 3 frames would have different source and destination addresses along the way.

But in its 802.3 ethernet frame, would the destination and source address in the 3 generated frames remain the same throughout with Computer B as the Destination Address and Computer A as the Source Address OR would the frame changes the Destination Address along to way to the Access Points ethernet address?


The destination address is the destination system, Computer B's MAC address.

The traffic's going to go through the access point because the client is associated to it (which is a different field in the 802.11 header, the recipient); the destination isn't the access point unless the access point is actually the final destination for the traffic on the layer two network - for instance, accessing its management interface or, if it's a router, sending traffic outside of the subnet.

802.11 was designed to work on many of the same principles of 802.11, which is why these access points can work just fine on the same layer 2 network as ethernet; just think of them like a switch with invisible cables to each associated client.

Yes, the frames need to be format-munged at each hop when changing media, but the headers always contain Computer B's MAC as the destination. Access Point 1 keeps track of the fact that Computer A's MAC address belongs to an associated client, while Computer B's MAC address is out whichever ethernet interface that Access Point 2 is plugged into.

Every switch or access point in the layer 2 network keeps track of what MAC addresses are accessible via a given interface, which is what allows each device handling a frame to independently make a decision about which interface to send it out of, be it wired or wireless.

  • The frame format of the 802.11 has 4 address fields and so it could keep track of all the MAC addresses. But in the Ethernet frame, it has only the destination and source address fields. So while travelling, the MAC addresses swap between the 4 fields in the 802.11 frame. But in the Ethernet frame, since there are only 2 address fields, do the source and destination addresses remain throughout with destination as Computer B's MAC address and source as Computer A's MAC address? – Taro Nov 17 '11 at 7:33
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    The destination MAC address will never change (to my knowledge). It's going to be either the MAC address of the destination host if the destination host is on the same layer 3 network or it's going to be the MAC address of the default gateway (router) if the destination host is on a different layer 3 network. The source MAC address will change if the destination host is on a different layer 3 network as the default gateway (router) will replace the original source MAC address with it's own MAC address. – joeqwerty Nov 17 '11 at 13:55
  • @Taro There are address fields for the transmitter and receiver, which are often not the same as the source and destination, which is why the frame has 4 fields. The destination of the frame is not changed in transit or translation between wired and wireless media. The transmitter and receiver for the wireless connection are obviously inconsequential on the wire; the source and destination fields are maintained. – Shane Madden Nov 17 '11 at 15:58

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