Re: [DNA-BOF] Using L2 to provide Instantaneous Movement Detection andNeighborhood Discovery

[Paul Tan <tanpaul@i2r.a-star.edu.sg>]

Title:

Hi all,

Bernard Aboba wrote:

I think that puting L3 information into L2 frames can be very relevant
for mobility operation. As we (IETF) need this information, it could be
good to work on this and have a consensus on what we need exactly. Then
we can submit our request to IEEE as the result of our work.
    

The problem is understanding the right L2 frames to include this
information in.  The Beacon and Probe Response are not secured, and also
are relatively early in the process so that they might not reflect the
actual VLAN that the station is assigned to.  

Assuming we agreed to 'advertise' L3 information in L2, wouldn't it be better if mobile stations can proactively discover their neighboring APs either thru active/passive scannings ?

Mobile stations can cache these L3 information, and maybe perform its 'choice of L3 handovers' or even initiates other operations (e.g. fast-handoff). I feel that we can perform several useful/critical operations if we obtained these 'reliable & valid' information before the actual L2 handover.

So probably the best that can be achieved in prior to association is to advertise *all* the prefixes
associated with a given BSSID.  

Are you referring/proposing a new message exchange prior to the actual Association message ? E.g. Pre-AssociationRequest (to obtain L3 information ON-DEMAND) ? I guess it is even harder to convince the 802.11 WG.

Even if the station perform association with a new AP, it can potentially associate with another neighboring AP at the next 'seconds'. Possible ?

This might be a single prefix (in the case
where the BSSID/SSID corresponds to a single VLAN) or it might be multiple
(in the case where the VLAN is dynamically assigned and can vary).  The
station can make its decision as to which AP to associate based on the
advertisements, but they are only a "hint" because it is possible that the
actual prefix to which the station is connected may not be the expected
one. The station will do a reachability test on the assumption that the
prefix is the expected one, but if this fails it must be prepared to
obtain an address by conventional means (DHCPv4, RS/RA, DHCPv6, etc.).

In my draft, I proposed that mobile stations maintain a table of all its neighborhood APs/ARs. For each AP (BSSID), MN can learn the network prefix or other L3 information for this AP. Therefore, after L2 handover is completed, MN should be able to tell IMMEDIATELY using this table if it has moved again. Right ?