Subject: [manet] Valid Destination Sequence Number flag in RFC3561

From: Takaaki MORIYA <[email-masked]>
Date: Fri, 10 Oct 2003 20:08:18 +0900

Hello everyone;

I have two questions about RFC 3561. I think that the statements about
valid sequence number flag are somewhat confusing.

Question 1:
I cannot understand how valid sequence number flag works.
In section 6.5,

> When a node receives a RREQ, it first creates or updates a route to
> the previous hop without a valid sequence number (see section 6.2)

This sentence means "When a node receives a RREQ, creates or updates a
route to the previous hop and the valid sequence number flag of the
route is marked as invalid." ?  Even if the flag is set as invalid, the
node re-sets the flag as valid when it receives HELLO pakcet from the
previous hop. So the flag often changes in some cases.

The other areas in the RFC document do not clearly refer to
valid sequence number flag. Does this flag show which message(HELLO
packet from the previous node or RREQ from the other node) initiates the
node to create the route? ("false" means that the route is created by
RREQ and "valid" means that the route is created by HELLO) 

For what purpose does route table entry need a flag of sequence number ?

Question 2:
Please let me confirm which status(true or false) is set to the valid
sequence number flag in the following two cases.

First, section 6.11 about route error says,

> 1. The destination sequence number of this routing entry, if it
> exists and is valid, is incremented for cases (i) and (ii) above,
> and copied from the incoming RERR in case (iii) above.
> 2. The entry is invalidated by marking the route entry as invalid
> 3. The Lifetime field is updated to current time plus DELETE_PERIOD.
> Before this time, the entry SHOULD NOT be deleted.

This paragraph does not refer to valid sequence number flag, but it
seems valid sequence number flag remains true. Is it right?

And second, Section 6.3 about route request says:

> Destination Sequence Number field in the RREQ message is the last
> known destination sequence number for this destination and is copied
> from the Destination Sequence Number field in the routing table. If
> no sequence number is known, the unknown sequence number flag MUST be
> set. 

In case of invalid sequence number in the node's existing entry, the
unknown sequence number flag is set?

Thanks in advance.
-- 
Takaaki MORIYA <[email-masked]>

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From: Ian Chakeres <[email-masked]>
Date: Fri, 10 Oct 2003 10:21:53 -0700

Comments in-line.

>Takaaki MORIYA wrote:

(1) The purpose of the valid sequence number flag in routing table
entries (and RREQ) is to indicate whether the sequence number is known
or not. This is important when updating route table entries and
creating RREQ. For example, if the sequence number for a particular
destination is not known and you need to generate a RREQ. The node
needs must set the unknown sequence number bit in the RREQ. Otherwise
the value of the sequence number field could screw up the sequence
number (and routing table) at other nodes that receive the RREQ,
because of the way sequence numbers are compared.

>seems valid sequence number flag remains true. Is it right?

The valid sequence number flag does not change state. 

>unknown sequence number flag is set?

Yes. See above comment (1).