Subject: Re: [Pana] Lost answer problem (a new issue)

From: Rafael Marin Lopez <[email-masked]>
Date: Thu, 01 Jul 2004 17:22:03 +0200

Hi Yoshihiro

Yoshihiro Ohba wrote:

>There might be some cases in which a PaC or a PAA might need to send a
>duplicate answer to a retransmitted old request (as well as a fresh
>answer to a new request if any) considering that an answer message for
>an old request can be lost. 
>
> Without this, a PANA session may stall in
>a way that the requester keeps retransmitting the old request while
>the responder may keep discarding them with waiting for a new request.
>The cases are described below.
>
>- When a PaC sends a PANA-Start-Answer message in response to a valid
>PANA-Start-Request message without a Cookie AVP, the answer message
>can be lost.  The PANA-Start-Request would be retransmitted.  To deal
>with the case, it might be better for the PaC to return a duplicate
>PANA-Start-Answer message after the PaC has been sent the first
>PANA-Start-Answer message until the PaC receives a valid
>PANA-Auth-Request message.
>  
>
In this case, I guess PANA-Start-Request would be retransmitted by
updating transmission sequence number , and PANA-Start-Request by
udpating transmission and received sequence numbers). That is:

PaC PAA

PSR(x,0)
<---------------------
PSA(y,x)
---------X--------->
PSR(x+1,0)
<-------------------
PSA(y+1,x+1)
------------------->

Am I wrong?

>- When a PaC sends a PANA-FirstAuth-End-Answer message in response to a
>valid PANA-FirstAuth-End-Request message (remember that a
>PANA-FirstAuth-End exchange is used for delimiting the first and
>second EAP authentications), the answer message may be lost.  The
>PANA-FirstAuth-End-Request would be retransmitted (with updating
>transmission sequence number).  To deal with the case, it might be
>better for the PaC to return a duplicate PANA-FirstAuth-End-Answer
>message (with updating transmission and received sequence numbers)
>after the PaC has been sent the first PANA-FirstAuth-End-Answer
>message until the PaC receives a valid PANA-Auth-Request message for
>the second EAP authentication.
>
>- When a PaC sends a PANA-Bind-Answer message in response to a valid
>PANA-Bind-Request message, the answer message can be lost.  As as
>result, the PAA will retransmit the PANA-Bind-Request (but with using
>a different transmission sequence number).  To deal with the case, it
>might be better for the PaC to return a duplicate PANA-Bind-Answer
>message (but with using different transmission and received sequence
>numbers) for a while after the first PANA-Bind-Request was received.
>The same thing can also apply to a PANA-Address-Update-Answer message
>that is sent by a PaC.
>
>- When a PaC or a PAA sends a PANA-Termination-Answer message in
>response to a valid PANA-Termination-Request message, the answer
>message can be lost.  As as result, the requester will retransmit the
>request (but with using a different transmission sequence number).  To
>deal with the case, it might be better for the sender of the answer to
>return a duplicate answer (with using different transmission and
>received sequence numbers) for a while after the first
>PANA-Termination-Request was received.  The same thing can also apply
>to a PANA-Reauth-Answer message that is sent by a PaC or a PAA.
>
>Those could improve robustness of the PANA protocol against loss of
>answer message.
>
>Comments?
>
>Yoshihiro Ohba
>
>_______________________________________________
>Pana mailing list
>[email-masked]
>https://www1.ietf.org/mailman/listinfo/pana
>
>
>  
>

-- 
------------------------------------------------------
Rafael Marin Lopez
Faculty of Computer Science-University of Murcia
30071 Murcia - Spain
Telf: +34968367645    e-mail: [email-masked]
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---

From: Yoshihiro Ohba <[email-masked]>
Date: Sat, 17 Jul 2004 17:18:04 -0400

Hi Rafa,

> udpating transmission and received sequence numbers). That is:

With incrementing the transmission sequence numbers in PSR and PSA
before the two entities complete initial sequence number negotiation,
it is possible to fail to share the same pair of initial sequence
numbers between PaC and PAA.  So sequence numbers should not be
incremented in PSR and PSA.  I think section 4.1.4 should be more
specific on this.

Yoshihiro Ohba

---

From: Rafael Marin Lopez <[email-masked]>
Date: Fri, 02 Jul 2004 09:55:47 +0200

Hi Yoshihiro... see my comments below

Yoshihiro Ohba wrote:

>numbers between PaC and PAA.
>
I guess you mean : PANA session stores ISN_Pac and ISN_PAA values and if
transmission sequence numbers are incremented (as in example) ISN_Pac
and/or ISN_PAA has not good values.

Becuase I cannot see problem when ISN_PaC and ISN_PAA are equal. could
you clarify it?

>  So sequence numbers should not be
I think so as well

Regards.

---

From: Yoshihiro Ohba <[email-masked]>
Date: Sun, 18 Jul 2004 09:16:54 -0400

> and/or ISN_PAA has not good values.

Yes.

> Becuase I cannot see problem when ISN_PaC and ISN_PAA are equal. could

I don't mean that ISN_PaC and ISN_PAA are equal.  

> >incremented in PSR and PSA.  I think section 4.1.4 should be more

OK, I will propose some text.

Yoshihiro Ohba