Subject: [netlmm] Retransmitting a PBU when HI=1 and MN LL ID is non-zero (draft-ietf-netlmm-proxymip6-18)

From: "Tero Kauppinen" <[email-masked]>
Date: Thu, 24 Jul 2008 12:58:16 +0200

Hello

Let's consider the following case where MAG sends a PBU where HI=1
(Attachment over a new interface) and MN LL ID is non-zero (no HNP).
When LMA receives the initial PBU it creates a new BCE and sends back a
PBA. If that PBA is lost, MAG will retransmit the PBU. If MAG leaves HI
to 1 (I didn't find any indication from the spec that it should do
otherwise) and retransmits the request, LMA will come to a conclusion
that this is 'Binding Lifetime Extension - After handoff'. This because:

Section 5.4.1.1. skipped (no HNP)
Section 5.4.1.2. hit (MN LL ID non-zero) checks 1) and 2) match -> a
request for updating an existing Binding Cache entry
Section 5.3.1. check 13 results in the third option (Binding Lifetime
Extension - After handoff) because HI=1

However, if HI would be set to a value of 5 (Handoff state not changed)
for retransmissions, LMA would choose (Binding Lifetime Extension- No
handoff) which I think should happen in this case. However, I'm still a
bit unsure if this would break some other cases. Even if the initial PBU
is not received by LMA, setting HI to 5 would result in the correct
behavior because there is no existing BCE with matching {MN ID, AT, MN
LL} triplet and thus LMA will create a new BCE regardless of the value
of HI.

Br,

Tero Kauppinen                                 Tel: +358 9 299 3057
Research Scientist, NomadicLab, IP Networks,   Fax: +358 9 299 3535
Ericsson Research, Corporate Unit.             Mobile: +358 40 590 7560
Oy L M Ericsson Ab
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From: Sri Gundavelli <[email-masked]>
Date: Thu, 24 Jul 2008 08:07:00 -0700 (PDT)

Hi Tero,

> that this is 'Binding Lifetime Extension - After handoff'. This because:

This is the correct behaviour. The LMA has the state for that session
and it should just update that session and not create a new session.
>From the MAG perspective, it never received the ACK and it just
retransmits the PBU with the same parameters, except seq num/time
stamp values.

> LL} triplet and thus LMA will create a new BCE regardless of the value

The MAG cannot set HI=5 (Re-Reg), we clearly require all the session
parameters in re-reg or de-reg messages. In this case, the MAG would not
even know the HNP as it never received the PBA.

Thanks
Sri

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From: "Tero Kauppinen" <[email-masked]>
Date: Tue, 29 Jul 2008 13:33:11 +0200

Hello

> The MAG cannot set HI=5 (Re-Reg), we clearly require all the 
> session parameters in re-reg or de-reg messages. In this 
> case, the MAG would not even know the HNP as it never 
> received the PBA.

If I blindly follow the rules written in Chapters 5.3. and 5.4., I end
up in the situation I described earlier -> handover (rules 5.4.1.2 1 and
2). There is no explicit requirement (following the rules in the
specified order) that if HI=5, the PBU must include all the session
parameters or at least none that I could fine.

I agree, it's not big of a deal; the binding in LMA will be updated
properly if the decision is either 'Binding Lifetime Extension- No
handoff' or 'Binding Lifetime Extension - After handoff'. Moreover,
tunnel and route setup functions can easily see that such routes and
tunnel already exist.

Regz,
Tero

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From: Sri Gundavelli <[email-masked]>
Date: Tue, 29 Jul 2008 04:59:05 -0700 (PDT)

Hi Tero,

> I agree, it's not big of a deal; the binding in LMA will be updated

Any case, we clarified this one line just before publication and
so this will be clear now. Either way, the session will be updated 
correctly.

Thanks
Sri

---

From: "Tero Kauppinen" <[email-masked]>
Date: Tue, 29 Jul 2008 16:29:31 +0200

Hello 

> Any case, we clarified this one line just before publication 
> and so this will be clear now. Either way, the session will 
> be updated correctly.

Okay, great.

Thanks,
Tero