[Olsr-dev] local broadcast/custom message types

[Henning Rogge]

On 02/21/2013 08:49 AM, Lotte Steenbrink wrote:
> As far as I/we understood it, the TTL that olsr routers (so in our
> case the nexus 7s) will decrement is the one in the olsr-header. If
> they get a packet that does not have this header, they will forward
> it to whatever hop they consider appropriate, flooding the subnet
> that forms our MANET with these broadcasts (and only the gateway node
> would actually decrement the IP TTL). So based on this assumption we
> figured it would be a better idea to make use of the already
> implemented header creation rather than build these packets from
> scratch... Is this assumption correct?

Similar, but not completely correct.

Have a look at the OLSR RFC:
http://tools.ietf.org/html/rfc3626#section-3.3

As you can see, every OLSR message (within the packet container) has a 
number of mandatory fields. You cannot have OLSR messages without them.

One of the fields is the TTL, the other one is the hopcount.

If you set the TTL of an OLSR message to 1 and the hopcount to 0, it 
will not be forwarded by the receivers (the same is done to the HELLO 
message).

Henning Rogge

-- 
Diplom-Informatiker Henning Rogge , Fraunhofer-Institut für
Kommunikation, Informationsverarbeitung und Ergonomie FKIE
Kommunikationssysteme (KOM)
Fraunhofer Straße 20, 53343 Wachtberg, Germany
Telefon +49 228 9435-961,   Fax +49 228 9435 685
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