Subject: [mobile-ip] FHv6: some comments

From: "Muhammad Jaseemuddin" <[email-masked]>
Date: Thu, 3 May 2001 16:48:06 -0400

Hi:

 I have following comments on FastHandoverv6 (FHv6) draft.

1. Page 3, first paragraph: 
    The mobile node sends a Fast Binding Update using its newly formed 
  COA as the last message before it executes the handover.  

  If the handover here means layer2 handover (before loss of layer 2
connection to the old AR) then how can mobile node use newCOA at the old
subnet to send Fast Binding Update (if thats what use means). Perhaps what
it should state is that the mobile can use oldCOA as the source address but
include newCOA in alternate COA option of F-BU.

2. Section 4.3.1 on F-BU is pretty much a cut and paste from Mobile IPv6
draft. 

3. Section 4.3.2 on F-BACK, last sentence of the first paragraph: there is
no A-bit definedd for F-BU. Either it is a legacy of Mobile IPv6 or A-bit
definition is missing in F-BU.

4. Section 3.1.2: HI-HACK exchange happens before old AR sends PrRtAdv to
the MN. Now, through out the draft it is maintmained that the MN cannot use
newCOA before receiving F-BACK. Since this is a stateful case and old AR has
received newCOA from the new AR and no new message exchange happens between
new AR and old AR sending F-BACK, there seems to be no need for mobile to
wait for F-BACK before sending packets through the new AR.

Cheers,
Muhammad Jaseemuddin		
Wireless Technology Lab		
Nortel Networks
email:   [email-masked]
Phone:  613 765-7520 (ESN 395)
Fax:      613 763-2686

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From: George Tsirtsis <[email-masked]>
Date: Thu, 3 May 2001 18:07:33 -0400

Hi Muhammad,

Comments below...

-----Original Message-----
From: Muhammad Jaseemuddin [mailto:[email-masked]]
Sent: Thursday, May 03, 2001 9:48 PM
To: [email-masked]
Subject: [mobile-ip] FHv6: some comments

Hi: 

GT> Correct me if I am wrong but that is also how the normal BUs
work...i.e.: when you send a BU you use the newCOA as source address....we
do the same with the F-BU...I think this is OK?

GT> It is intentionaly very similar...the BU fields we re-use have the same
semantics and thus the same description...I think that is a good think...

GT> Thanks...initially we had the A-flag but in the end we decided that the
F-BACK should be mandatory and thus the A-flag does not make sense...the
above escaped the deletion of this.....I will fix it.

GT> HI-HACK only allocates an address...remember that until the F-BU has
been received by the oldAR no routing change is taking place (i.e.: newCOA
is not yet in use). The fact that this is a stateful case does not change
the above....i.e: the oldAR may still reject the F-BU and thus the mobile
node MUST NOT use it until the FBACK is being received...

Thanks

George

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From: Mohan Parthasarathy <[email-masked]>
Date: Thu, 3 May 2001 16:50:30 -0700 (PDT)

> do the same with the F-BU...I think this is OK?
How about ingress filtering ? The normal BUs are sent after moving
to the new link to the new access router. Isn't F-BU sent to the old
Access router ? Are you assuming that the old Access router will not
filter this packet with the new care of address ? 

-mohan

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From: "Muhammad Jaseemuddin" <[email-masked]>
Date: Fri, 4 May 2001 10:02:11 -0400

Thanks George for your response.

> From:	George Tsirtsis [SMTP:[email-masked]]
> Sent:	Thursday, May 03, 2001 6:08 PM
> To:	[email-masked]'
> Subject:	RE: [mobile-ip] FHv6: some comments
> 
> Hi Muhammad,
> 
> Comments below...
> 
	[MJ]  As Mohan also pointed out, the newCOA can be used only from
the new subnet as a source address. But, the draft describes the case where
the MN sends F-BU from the old subnet to the old AR. Hence, in this case it
must not use newCOA. If the ingress filtering is set in the AR (I am saying
if because ingress filtering has become a thorny issue) then the packet will
be droped. And also it doesn't make sense, because newCOA is valid only on
new subnet in this situation where MN acquires new COA every time it changes
subnet.

> semantics and thus the same description...I think that is a good think...
	[MJ]  But, how about dangling references, for example reference to
section 9.3 that is not in the draft.

> node MUST NOT use it until the FBACK is being received...
	[MJ]  I understand it because of consistency reasons. Can we think
of any reason why old AR would deny MN to use new COA at the new AR.
Consider the following facts:

	1. According to FH draft (and Mobile IP principle) mobile ultimately
decides about the handover, hence old AR waits for F-BU before bicasting. In
the above case mobile has already sent a positive decision.

	2. New COA is controlled by the new AR.

	3. No additional exchange of messages happen between the old and new
AR, hence presumably no change of status of new AR would affect the F-BACK.

	4. Now, only some event at old AR can trigger a F-BACK that would
deny MN using new COA.

	First of all its not very clear what those events could be? It is
plausible that old AR would like to abort handover at this late stage for
some x,y reasons. But, the draft allows MN to use old COA interim at the new
subnet before receiving F-BACK with no assurance of packet delivery (and
this because of ingress filtering). Why not in this case allowing MN to use
new COA?
> George
	- Muhammad Jaseemuddin