0

Does an Autonomous AP have the ability to send a packet from a source in the BSS directly to a destination in the same BSS, without having to strip off the 802.11, replace with 802.3 and send to a switch? Would this have to DS=0, from DS = 0?

  • 3
    Whoever downvoted this and voted to close is on the wrong side of Dunning-Krueger. This is a perfectly clear question for anyone familiar with the 802.11 standard. Fellow SuperUsers, please don't downvote or vote to close a question just because you lack sufficient depth of knowledge in that subject. Please just keep scrolling to another question and leave the deep-knowledge questions to those of us who know the subject deeply. – Spiff Oct 3 '18 at 5:06
1

Yes, this is called "Intra-BSS Relay", and it is standard operation for all APs.

When clients A and B are in the same BSS (i.e. associated to the same AP), when client A needs to send a unicast packet to client B, it actually sends it to the AP. On this leg of its journey, it's ToDS=1, FromDS=0. Address 1 is the AP's MAC address (BSSID), Address 2 is client A's MAC address (Source) and Address 3 is client B's MAC address (Destination). If WPA or WPA2 is in use, the packet is encrypted with client A's unicast key and cipher.

Then the AP relays the packet to client B. On this leg of its journey, it's ToDS=0, FromDS=1. A1 is Client B's MAC (Destination), A2 is the AP's MAC (BSSID), and A3 is Client A's MAC (Source). If WPA or WPA2 is in use, the packet is encrypted with client B's unicast key and cipher.

The AP is always considered part of the Distribution System, even if it is completely standalone and not connected to any kind of backhaul network.

The 802.11 spec is independent of 802.3 and does not require any conversion of 802.11 headers to 802.3 at any time. Technically your DS, if any, needn't be 802.3 at all. However, most real-world devices that contain an 802.11 AP use 802.3 as their DS network, so those devices must translate packets to 802.3 if/when they need to be forwarded onto the 802.3 network.

You asked about ToDS=0, FromDS=0. That's used in IBSS (an ad-hoc network with no AP, thus no DS). In an IBSS, all peers send direct to all other peers because there is no AP to do IntraBSS Relay.

  • Thanks, that cleared a few things up, but you said 'is standard operation for all APs', I assume you mean autonomous APs because with a LAP, the traffic goes straight to the WLC via CAPWAP where the MAC table is stored. An autonomous AP would have a local MAC table I think that would enable it to perform that intra-BSS relay operation or choose to send it to the DS, which is why WLCs need to be local I believe, or use HREAP. – Lewis Kelsey Oct 4 '18 at 20:59
  • @LewisKelsey Your comment is riddled with Cisco proprietary implementation details that are not part of the IEEE 802.11 standard. 802.11 requires APs to relay frames from one wireless client to another. Whether your particular vendor's implementation chooses to do that by first sending them around the world via IPoAC (RFC1149) is a vendor-proprietary implementation detail and has nothing to do with the 802.11 standard itself. The terms "autonomous AP", "LAP", "CAPWAP", "WLC", and "HREAP" do not appear anywhere in IEEE 802.11-2016. – Spiff Oct 4 '18 at 21:41
  • @LewisKelsey Was your original Question meant to be specifically about how Cisco chooses to implement Cisco's concept of an "autonomous AP"? If so, my apologies, my answer was from a standard 802.11 point of view, without taking Cisco's proprietary implementation details into account. The 802.11 spec doesn't require APs to send packets over 802.3. I have no idea if any given Cisco 802.11-using product always sends packets over 802.3 or not. – Spiff Oct 4 '18 at 21:45
  • My original question was whether APs send everything to the switch (803.2/802.11 whatever, doesn't matter about the DS implementation), in a WLAN controllerless network. You answered that question by drawing my attention to Intra-BSS relay which makes sense. The real question now appertains to a network now with a WLC and whether APs that rely on an WLC for control and data have that local functionality of Intra-BSS relaying and local information of what STAs are connected to the AP, or is all this information stored at the WLC and does all data travel through it – Lewis Kelsey Oct 4 '18 at 22:04
  • But I admit the first question was a bit silly – Lewis Kelsey Oct 4 '18 at 22:06

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.