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New Member

MAC addressing across the DS

In an ESS, if a frame is being sent from a station in one BSS to a station in another BSS then that frame will cross the DS from one AP to another.

When the frame leaves the sending station the To DS bit will be set and the address 1 field will be the MAC of that station's AP. The address 2 field will be the MAC of the send station and the address 3 field will be the MAC of the destination station in the other BSS.

The frame will then cross the wired network from one AP to the other.

Now when the frame leaves the AP in the destination BSS the From DS bit will be set and the address 1 field will be the MAC of destination station. The address 2 field will be the MAC of this AP and the address 3 field will be the MAC of the sending station in the other BSS.

If any of this is incorrect please set me straight.

My question is when the frame is sent across the DS from the sender's AP to the receiver's AP what MAC addresses are used in the Etherent II frame? Since it's not an 802.11 frame, we have only a source and destination address not four address fields.

My follow-up question is when the sender's AP receives the frame from the sending station how does it know to send it to the receiver's AP? In other words, how does it know that it's a station in a BSS and not a wired station (assuming the wired station was in the same broadcast domain)?

TIA,

Brad

4 REPLIES
New Member

Re: MAC addressing across the DS

I was really hoping some of you smart people would have an answer. I guess I stumped you.

Hall of Fame Super Silver

Re: MAC addressing across the DS

That is a very good question.....

The AP is a hub and has all the arp entries for all the stations associated to it. So if a device is not in the arp table, the frame will be forwared out all interfaces except for the interface it heard the frame from.... just like a hub.

Makes sense?

-Scott
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New Member

Re: MAC addressing across the DS

Do you mean a switch/bridge? A hub/repeater does not maintain an ARP table, it always floods the frame.

Hall of Fame Super Silver

Re: MAC addressing across the DS

don't know what I was thinking... It's like a hub.

-Scott
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