Subject: RE: [manet] AODV : receiving and forwarding route replies

From: [email-masked]
Date: Wed, 6 Oct 2004 09:40:00 +0200

John,

Thank you for your comments.
AODV must behave as you describe when intermediate node are allowed to reply
to RREQ concerning destination they have a route "fresh enough" to.

>From section 6.6 on p18 :
A node generates a RREP if either
(i) it is itself the destination or,
(ii) it has an active route to the destination, the destination sequence
number in the node's existing route table entry for the destination is valid
and greater than or equal to the destination sequence number of the RREQ,
and the "destination only" ('D') flag is NOT set

So if the "destination only" flag is set in the RREQ, an intermediate node
will not generate a RREP in response to any RREQ.
I think that if the sequence number of station S4 is not modified, the case
illustrated by the example below is incorrectly handled in RFC 3561.

>Let's consider the following network :
>
>S1 --- S2 --- S3 --- S4
>
>First, S2 establishes a route to S4.
>Then S1 wants to do the same thing. If intermediate node reply is not
>activated, the route research reaches S4, that sends a RREP back to S1.

>Nevertheless, in section 6.7 of RFC 3561 a node forwards a RREP only if

>a forward route (to the destination) has been updated (or created). As
>this is not the case here, the RREP is not forwarded and the route to
>S4 is never established on S1.

This means that either :
- "destination only" flag in RREQs must never be set to 1 or,
- a RREP is always forwarded, even if it does not cause an update to the
route to the destination (opposite to what is written in RFC 3561, section
6.7 page 21)

	Raphaël

-----Message d'origine-----
De : John Mullen [mailto:[email-masked]]
Envoyé : mardi 5 octobre 2004 20:06
À : [email-masked]
Cc : [email-masked]
Objet : RE: [manet] AODV : receiving and forwarding route replies

Hi Raphael,

>From Section 2 on p. 3,

   As long as the endpoints of a communication connection have valid
   routes to each other, AODV does not play any role.  When a route to a
   new destination is needed, the node broadcasts a RREQ to find a route
   to the destination.  A route can be determined when the RREQ reaches
   either the destination itself, or an intermediate node with a 'fresh
   enough' route to the destination.  A 'fresh enough' route is a valid
   route entry for the destination whose associated sequence number is
   at least as great as that contained in the RREQ.

>From the last line, if the route is fresh enough, S2 sends a RREP back
to S1.  If not, when the RREQ propagation continues to S4, the
destination sequence number will be higher (otherwise the route is fresh
enough).  From p. 12, one of the cases in which a node increments its
sequence number is:

   -  Immediately before a destination node originates a RREP in
      response to a RREQ, it MUST update its own sequence number to the
      maximum of its current sequence number and the destination
      sequence number in the RREQ packet.

So, if the route is not "fresh enough," the destination will increment
its own sequence number.  (Otherwise it won't see the RREQ).  This means
that by the time you get to Section 6.7, either the RREP is simply
confirming the known route, in which case S2 need not reply to S1
because it already did so earlier, or it is indicating some sort of
better route from S2 to S4, in which case S2 will forward the RREP to S1
to correct its earlier misinformation. 

At least, that is how I understand it.

John Mullen

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of [email-masked]
Sent: Monday, October 04, 2004 11:22 PM
To: [email-masked]; [email-masked]
Subject: RE: [manet] AODV : receiving and forwarding route replies

Hi,

The destination sequence number of station D is only updated when :
- the station D itself sends a RREQ
- a route to the D is broken. In that case, the node whose link to the D
is broken increments the destination sequence number of D. Later, this
node sends AODV messages with updated sequence number for destination D.

In the example below, the sequence number of S4 is never updated. It is
the reason why S3 never propagates the RREP message corresponding to the
RREQ originated at S1.

Anyhow, it is the way I have understood RFC 3561. If I am wrong, I would
like somebody to tell me what is not correct in my understanding.

        Raphaël

-----Message d'origine-----
De : Yann -EADS- [mailto:[email-masked]]
Envoyé : lundi 4 octobre 2004 18:02
À : [email-masked]
Objet : RE: [manet] AODV : receiving and forwarding route replies

Hello,

I guess that the forward route is actually updated upon receiving the
RREP.
In my mind, the sequence number received by S2 is greater than the one
which

created its route to S4. And if this route is updated, it fowards the
RREP
to S1.

Am I wrong ?

>From: [email-masked]
>To: [email-masked]
>Subject: [manet] AODV : receiving and forwarding route replies
>Date: Mon, 4 Oct 2004 17:18:18 +0200
>
>Hi all,
>
>As it is described in RFC 3561, AODV incorrectly handles RREP
>forwarding when route reply by intermediate nodes is not activated.
>Let's consider the following network :
>
>S1 --- S2 --- S3 --- S4
>
>First, S2 establishes a route to S4.
>Then S1 wants to do the same thing. If intermediate node reply is not
>activated, the route research reaches S4, that sends a RREP back to S1.

>Nevertheless, in section 6.7 of RFC 3561 a node forwards a RREP only if

>a forward route (to the destination) has been updated (or created). As
>this is not the case here, the RREP is not forwarded and the route to
>S4 is never established on S1.
>
>Any comment ?
>
>       Raphaël
>
>
>_______________________________________________
>manet mailing list
>[email-masked]
>https://www1.ietf.org/mailman/listinfo/manet

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---

From: "John Mullen" <[email-masked]>
Date: Wed, 6 Oct 2004 09:32:46 -0600

Hi Raphael,

What you say is true, but just before the destination generates a RREP,
it will increment its sequence number.  This would cause S2 to forward
the RREP back to S1, since the RREP would indicate S2's current routing
table entry is invalid, due to it having an older destination sequence
number.

I was just thinking.  What we really need is a complete state diagram
for AODV.

:-)

John Mullen

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]] 
Sent: Wednesday, October 06, 2004 12:40 AM
To: [email-masked]
Cc: [email-masked]
Subject: RE: [manet] AODV : receiving and forwarding route replies

John,

Thank you for your comments.
AODV must behave as you describe when intermediate node are allowed to
reply to RREQ concerning destination they have a route "fresh enough"
to.

A node generates a RREP if either
(i) it is itself the destination or,
(ii) it has an active route to the destination, the destination sequence
number in the node's existing route table entry for the destination is
valid and greater than or equal to the destination sequence number of
the RREQ, and the "destination only" ('D') flag is NOT set

So if the "destination only" flag is set in the RREQ, an intermediate
node will not generate a RREP in response to any RREQ. I think that if
the sequence number of station S4 is not modified, the case illustrated
by the example below is incorrectly handled in RFC 3561.

This means that either :
- "destination only" flag in RREQs must never be set to 1 or,
- a RREP is always forwarded, even if it does not cause an update to the
route to the destination (opposite to what is written in RFC 3561,
section 6.7 page 21)

	Raphaël

-----Message d'origine-----
De : John Mullen [mailto:[email-masked]]
Envoyé : mardi 5 octobre 2004 20:06
À : [email-masked]
Cc : [email-masked]
Objet : RE: [manet] AODV : receiving and forwarding route replies

Hi Raphael,

John Mullen

-----Original Message-----

Hi,

        Raphaël

-----Message d'origine-----
De : Yann -EADS- [mailto:[email-masked]]
Envoyé : lundi 4 octobre 2004 18:02
À : [email-masked]
Objet : RE: [manet] AODV : receiving and forwarding route replies

Hello,

I guess that the forward route is actually updated upon receiving the
RREP. In my mind, the sequence number received by S2 is greater than the
one which

RREP to S1.

Am I wrong ?

---

From: manet user <[email-masked]>
Date: Wed, 6 Oct 2004 12:59:20 -0700 (PDT)

Check this link regarding Dest Seq Num update while sending RREP. Check the previous and follow up messages as well.
 
http://www1.ietf.org/mail-archive/web/manet/current/msg02593.html
 
-MU

John Mullen <[email-masked]> wrote:
Hi Raphael,

:-)

John Mullen

-----Original Message-----

John,

This means that either :

Raphaël

-----Message d'origine-----
De : John Mullen [mailto:[email-masked]]
Envoyé : mardi 5 octobre 2004 20:06
À : [email-masked]
Cc : [email-masked]
Objet : RE: [manet] AODV : receiving and forwarding route replies

Hi Raphael,

John Mullen

-----Original Message-----

Hi,

Raphaël

-----Message d'origine-----
De : Yann -EADS- [mailto:[email-masked]]
Envoyé : lundi 4 octobre 2004 18:02
À : [email-masked]
Objet : RE: [manet] AODV : receiving and forwarding route replies

Hello,

Am I wrong ?

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---

From: "John Mullen" <[email-masked]>
Date: Wed, 6 Oct 2004 14:53:02 -0600

Hmm,
 
Seems there *is* a problem.
 
:-)
 
We can't just say never set the destination only flag, because that is
used to force a search through to the destination when the originator
suspects that a "valid" sub route is actually invalid.  I think a
cleaner solution is to say "always forward the RREP back towards the
originator if the destination only flag is set."  This condition could
be kept in the table entry, but a cleaner approach would be to add a
flag to the RREP packet, perhaps using one of the reserved bits, or
simply call such a RREP packet one of Type 5.
 
John Mullen

-----Original Message-----
From: manet user [mailto:[email-masked]] 
Sent: Wednesday, October 06, 2004 12:59 PM
To: John Mullen; [email-masked]
Cc: [email-masked]
Subject: RE: [manet] AODV : receiving and forwarding route replies

Check this link regarding Dest Seq Num update while sending RREP. Check
the previous and follow up messages as well.

-MU

Hi Raphael,

:-)

John Mullen

-----Original Message-----

John,

>activated, the route rese! arch reaches S4, that sends a RREP back to
S1.

This means that either :

Raphaël

-----Message d'origine-----
De : John Mullen [mailto:[email-masked]]
Envoyé : mardi 5 octobre 2004 20:06
À : [email-masked]
Cc : [email-masked]
Objet : RE: [manet] AODV : receiving and forwarding route replies

Hi Raphael,

>From Section 2 on p. 3,

As long as the endpoints of a communication connection ha! ve valid

- Immediately before a destination node originates a RREP in
response to a RREQ, it MUST update its own sequence number to the
maximum of its current sequence number and! the destination
sequence number in the RREQ packet.

John Mullen

-----Original Message-----

Hi,

The destination sequence number of station D is only updated ! when :

Raphaël

-----Message d'origine-----
De : Yann -EADS- [mailto:[email-masked]]
Envoyé : lundi 4 octobre 2004 18:02
À : [email-masked]
Objet : RE: [manet] AODV : receiving and forwarding route replies

Hello,

I guess that the forward route is actually updated upon receiving the
RREP. In my mind, the sequence number received by S2 is gr! eater than
the
one which

Am I wrong ?

>this is not t! he case here, the RREP is not forwarded and the route to