Subject: RE: [mobile-ip] New Draft on FMIPv6 over 802.11

From: [email-masked]
Date: Tue, 1 Oct 2002 14:36:09 -0500

> > 
> > Hi Pete,
> > 
> > >  > Can mobile node still send a re-association message even though
> > >  > it's now trying to associate with an AP in another ESS? 
> > >  > If we can use re-association "only" when the mobile is moving
> > >  > within the same ESS, than what is the use? The mobility would
> > >  > be already handled by L2 mechanisms, right?
> > > 
> > > An ESS can cover multiple IP subnets.
> > 
> > But this still doesn't answer my question though.
> > As long as the mobile moves within the same ESS,
> > wouldn't/shouldn't distribution system (DS)
> > handle the mobility?
> 
> No.

Or more accurately, Not necessarily. "Link layer mobility
within an ESS is supported in 802.11 only if the backbone
network is a single link-layer medium such as shared Ethernet
or a VLAN" (quoting from Matthew S. Gasts 802.11 Wireless Networks
O'Reilly book)

> > alper

-Basavaraj

---

From: Pete McCann <[email-masked]>
Date: Wed, 2 Oct 2002 09:59:45 -0500

> or a VLAN" (quoting from Matthew S. Gasts 802.11 Wireless Networks

Just to elucidate this point a bit further: the only mobility scheme
defined by 802.11 within a DS is the 802 XID (link layer update frame)
which will update any connected Ethernet bridges, but will not
traverse IP routers.

It is easy to confuse the notion of ESS with the notion of IP subnet
(I did this myself when I first started looking at the documents) but
there is not necessarily a one-to-one correspondence between them.  An
ESS is just the collection of all APs that advertise the same SSID.
That could be one subnet or many subnets.  If you move within a
subnet, the XID frame takes care of your mobility.  If you move
between two subnets, you need Mobile IP if you want to keep your IP
address.  If basic Mobile IP isn't fast enough, you need Fast Mobile
IP.

-Pete

---

From: Behcet Sarikaya <[email-masked]>
Date: Wed, 02 Oct 2002 11:59:35 -0500

Well, 802.11 link layer handoff is basically (re)association 
establishment after a scan by MN and nAP broadcasting the newcomer's 
MAC@  on the wired link so that oAR deletes it.
Regards,

-- 
Behcet

---

From: "Alper E. YEGIN" <[email-masked]>
Date: Wed, 2 Oct 2002 13:31:04 -0700

> address.  If basic Mobile IP isn't fast enough, you need Fast Mobile

We are re-using certain L2 handover features (e.g., re-association) 
for a L3 handover. I think we need to work out some details to 
understand our approach can co-exist with the L2 mechanisms and 
not interfere. 

- Tunnel based approach requires use of re-association message.
- Reassociation message is used when MN moves within the same ESS.
- Therefore, although different APs might belong to different IP
  subnets, they need to advertise the same ESSID.
- We might have independent ESS with separate DS, but sharing the
  same ESSID. 

Are there any issues here? For example:
   - can the AP handle "re-association" even if the MN is coming from
     an AP that belongs to another ESS?
   - MN's request to "re-associate" can be at best handled as a 
     request to "associate" by the new AP. Is this OK for the MN?
   - How does the DS handle a client's re-associate request if this is
     the first request?

Some of these details needs to be covered in the draft, imo. Especially,
having to configure the same ESSID on two adjacent ESS.

alper

---

From: Pete McCann <[email-masked]>
Date: Fri, 4 Oct 2002 14:38:21 -0500

Hi, Alper,

Some comments below (sorry for the late response):

 > - Tunnel based approach requires use of re-association message.

Yes.

 > - Reassociation message is used when MN moves within the same ESS.

Yes.

 >   subnets, they need to advertise the same ESSID.

Yup.

 > - We might have independent ESS with separate DS, but sharing the

The "DS" is a fuzzy concept.  I think we can use the entire Internet
as a DS, if we want, as long as all the APs are connected to it.

 >      an AP that belongs to another ESS?

Technically it should work as long as you can make the connection
between an AP's link-layer address and some IP-layer address, and as
long as you can bootstrap the security somehow.  You may need the help
of a RADIUS server (with proxies?) to do this if your relationship
with the previous AP is sufficiently "loose".

 >      request to "associate" by the new AP. Is this OK for the MN?

It would work but you would lose the ability to speed up the
association process with the use of information from the previous AP.
You would have to start 802.1X or PANA from scratch (unless
pre-authentication was an option).  It still might be possible to use
F-BU with the old AR; however, it's not clear how much that buys you
if the link-layer handoff itself involves round-trips through AAA back
to a home network.

 >    - How does the DS handle a client's re-associate request if this is

I.e., if there is no previous association state found at the indicated
AP?  I think it would be similar to the case where the old AP is not
reachable via IAPP - you would start from scratch with 802.1X or PANA.

 > having to configure the same ESSID on two adjacent ESS.

Yes.  I tried to indicate that in the ESS definition but I will work
to expand on it in the next version.

-Pete

---

From: Behcet Sarikaya <[email-masked]>
Date: Fri, 04 Oct 2002 16:10:10 -0500

>address.  If basic Mobile IP isn't fast enough, you need Fast Mobile
Exactly. 7.3.2.1 in IEEE 8802-11-1999 defines it.
ESSID is kind of network name (of 0-32 octets) assigned by the 
administrators.

>to expand on it in the next version.

I am not sure if Pete's draft has to talk more about this.

-- 
Behcet

---

From: "Alper E. YEGIN" <[email-masked]>
Date: Fri, 4 Oct 2002 17:14:29 -0700

Hi Pete,

> reachable via IAPP - you would start from scratch with 802.1X or PANA.

My understanding is that, this "reassociation request" would fail,
and return a response with code "11 reassociation denied due to inability
to confirm that association exists". Then what happens? Would the
MN try again, try "association request", or ?

Basically this MN shouldn't have sent a "reassociate request" to this
AP in another ESS. We tricked it into doing this because we set the ESSID
on two separate ESS to the same value. 802.11 spec clearly says
"Reassociation
frames shall only be sent if the sending STA (MN) is already associated
in the same ESS".( top of page 23, Edition 1999).

alper

---

From: Pete McCann <[email-masked]>
Date: Mon, 7 Oct 2002 09:37:28 -0500

Hi, Alper,

Alper E. YEGIN writes:
 > to confirm that association exists".

Maybe, but not necessarily - as I understand it IAPP is an optional
feature, so in general there might not be any communication with the
old AP.  It seems like you should then treat reassociation requests
just as if they were association requests.

 > Then what happens? Would the

You would be left in State 2, so your option would be to do either
association or reassociation.  Presumably an implementation should
choose to try an association as it would have a better chance of
success.

 > in the same ESS".( top of page 23, Edition 1999).

If the ESSIDs are the same then by definition that is the same ESS.
Remember, a DS can be the whole Internet if necessary.

If you haven't done the work to put security associations in place
between neighboring APs (possibly via RADIUS), and if you want to use
IAPP for handoff, you shouldn't have broadcast the same ESSIDs.

-Pete