Subject: [manet] draft-ietf-manet-dymo-24.txt: handling route timeouts

From: Levente Mészáros <[email-masked]>
Date: Wed, 2 Jan 2013 16:47:43 +0100

Hi,

I'm writing a simulation model for DYMO using OMNeT++ and I'd like
to ask for your help in interpreting some details of the draft.

Chapter "6.3. Route Table Entry Timeouts" says:

"During normal operation, AODVv2 does not require any explicit
 timeouts to manage the lifetime of a route.  However, the route table
 entry MUST be examined be before using it to forward a packet, as
 discussed in Section 8.1.  Any required expiry or deletion can occur
 at that time.  Nevertheless, it is permissible to implement timers
 and timeouts to achieve the same effect.
 ...
 A route MUST be expunged if Current_Time >= Route.ExpirationTime."

Chapter "8.1.  Handling Route Lifetimes During Packet Forwarding" says:

"If Current_Time > Route.ExpirationTime, the route table entry has
 expired, and a RERR SHOULD be generated."

If I expunge expired routes using timers, when should I generate RERR
messages? With this approach there are no expired routes when packets
are forwarded. Also, when the route timer expires and the route is removed,
there is no associated data packet to be forwarded, and there may have
not been any at all.

Thank you for your help.
Best regards,
Levente Mészáros

---

From: "Charles E. Perkins" <[email-masked]>
Date: Wed, 02 Jan 2013 09:58:15 -0800

Hello Levente,

As you point out, if the route is expunged when a timer alarm occurs, it
is unlikely there will be a data packet affected, so no RERR is transmitted.
In fact, any other router that has the same route is likely to have it
marked as expiring at the same time, so the RERR would not offer
any benefit.

RERRs are intended to avoid transmission of unrouteable packets.
Expunging routes which have expired would typically not affect the
routability of any packets.

If you can suggest inclusion of text to make this more clear, that would
be appreciated!

Regards,
Charlie P.

On 1/2/2013 7:47 AM, Levente Mészáros wrote:
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-- 
Regards,
Charlie P.