Subject: Re: [netlmm] Lack of session indication

From: "Soininen Jonne (NSN FI/Espoo)" <[email-masked]>
Date: Thu, 11 Sep 2008 18:22:03 +0300

Hi Vijay,

On 8/29/08 9:01 PM, "ext Vijay Devarapalli" <[email-masked]> wrote:

> Hi Jonne,
> 
> Soininen Jonne (NSN FI/Espoo) wrote:
>> Hello,
>> 
>> Sorry to be late in this. However, I'll try to summarize some things here
>> and understand what should be done going forward. Please, tell me if I got
>> it right:
>> 
>> The issue is that there may be situations where LMA may lose the binding
>> cache for a user or a complete MAG:
>> 
>> 1) Session revocation in the LMA without notification to the MAG
> 
> This should trigger a binding revocation from the LMA to the MAG. If the
> binding revocation indication message is lost, it is re-transmitted.

First of all, these are not necessarily my opinions how this should work.
I'm just trying to understand how something like this would work.

I think it was brought up that there is a possible situation where there is
no session revocation notification implemented in the system (for instance
the system is implemented before MEXT has finished its work). Basically, LMA
has decided that the binding is not needed or allowed anymore, but has no
way of telling it to the MAG.

> 
>> 2) LMA reboot
> 
> If the PMIPv6 session state survives reboots, then there is nothing to
> do. If it does not, the loss of session state is detected by the
> unsolicited Heartbeat response message with the restart counter
> incremented by 1. In fact, it would be very bad if the LMA has to
> respond with a "lack of session indication" message for each of the
> mobile nodes it had a binding for.

This is exactly why I'm trying to ask how these different mechanisms would
work together. I'm a bit worried if there are multiple mechanisms to deal
with error situations that might have overlapping or interconnected usages.
This might have unexpected consequences for the system.
> 
>> 3) A different software error.
> 
> You mean a bug? Since when did we extend protocols to handle bugs. ;)

There were other software errors (memory corruption, etc.) that were
mentioned in the mails before mine. If people were thinking about bugs, I
don't know... ;)

> 
>> Some of the people in the discussion feel that it is a problem that the MAG
>> keeps on sending traffic to the LMA until the timer kicks in and the MAG
>> tries to do a new PBU.
>> 
>> What has been proposed is a notification from the LMA to the MAG to tell
>> there is no binding cache.
>> 
>> I have myself some questions on this topic. Would a possible notification
>> trigger a new PBU or dropping the connection at MAG? What would be the
>> security model? (Basically, how to make sure there is not a DoS attack by
>> spoofing a fake notification?) How would this work together with the other
>> heart beat mechanisms, etc?
> 
> I don't think we have yet come up with a scenario where the "MN-specific
> lack of session indication" would be needed.
> 
> Then there is an issue of whether the LMA should silently drop the
> messages or should send some sort of message back to the MAG. We haven't
> resolved that yet.
> 
> Finally, if we do conclude that the LMA should send a message back, we
> need to decide between sending a Binding Error and an ICMP error
> message. Sending a Heartbeat message seems to be a poor choice, since
> Heartbeat messages are for testing path reachability between the MAG and
> the LMA and are not specific to any particular mobile node's session.

The question from my part is, do we need this type of a session indicator,
and if we do how can we make sure it is secure, and what kind of reaction
should the indication trigger in the MAG.

Cheers,

Jonne.

> Hope that helps.
> Vijay

-- 
Jonne Soininen
Nokia Siemens Networks

Tel: +358 40 527 46 34
E-mail: [email-masked]

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---

From: Vijay Devarapalli <[email-masked]>
Date: Thu, 11 Sep 2008 10:59:47 -0700

Hi Jonne,

> way of telling it to the MAG.

Yes, this is possible. If the binding revocation mechanism is not used 
(or not implemented), then you could end up in a state where the MAG 
thinks there is a binding, but the LMA does not have a binding.

> The question from my part is, do we need this type of a session indicator,

We need to address this question first. From what I have seen on the 
mailing list so far, it looks like we don't need this "lack of session 
indication message" from the LMA to the MAG.

> and if we do how can we make sure it is secure, 

This is not difficult.

> and what kind of reaction

We should use the Binding Error message, IMO.

Vijay