[Olsr-dev] OLSRd 0.6.0 with ETT available

Henning Rogge (spam-protected)
Fri Oct 8 15:40:33 CEST 2010

On Fri October 8 2010 10:11:57 David Lamparter wrote:
> On Thu, Sep 30, 2010 at 02:02:25PM +0200, Henning Rogge wrote:
> > I have a question on your encoding of the ETT values in the Hello/TC
> > messages.
> > 
> > In the HELLO messages you seem to be using a 5 byte encoding. OLSR
> > messages have to be 4-byte aligned, so you want to add 3 bytes of
> > padding there. It might crash your nodes on an ARM/MIPS cpu otherwise.
> Um, what kind of crap is this? The padding in OLSR is not only
> unneccessary but even harmful as it wastes airtime.
If you look into the OLSR RFC you will notice two things:

1.) all OLSR messages have a length of 4*x bytes
2.) all fields in OLSR messages are "well aligned"

Even the original ETX extension enlarged the messages by 4 bytes (with 2 bytes 

I was pretty sure that it's somewhere in the RFC, but I was unable to find it.

The OLSRd core and most of it's plugins was written with this assumption and 
nobody changed it up to version 0.6.0. If you have a message with a length 
with is not a multiple of 4, bad things will happen.

We had a case like this last year in Berlin. It took us 3 weeks to find the 
problem. After this OLSRd got a check if incoming messages have a "correct" 
size... if not the rest of the packet is dropped.

The problem will not be there in 0.7.0, because the new packet parser for 
PacketBB (RFC 5444) will handle this stuff.

Henning Rogge

Diplom-Informatiker Henning Rogge , Fraunhofer-Institut für
Kommunikation, Informationsverarbeitung und Ergonomie FKIE
Kommunikationssysteme (KOM)
Neuenahrer Straße 20, 53343 Wachtberg, Germany
Telefon +49 228 9435-961,   Fax +49 228 9435 685
mailto:(spam-protected) http://www.fkie.fraunhofer.de
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