[Olsr-dev] olsrd + bmf plugin

Erik Tromp (spam-protected)
Thu Mar 17 22:32:28 CET 2011

I don't think so. I don't have a lot of knowledge about the implementation
of mDNS and p2p, so I cannot really judge about those. But the problem is
not related to the forwarding algorithm itself, more in the mechanism of
capturing outgoing packets, and interworking of that mechanism with the
forwarding algorithm.

The technical details:

If an IP local broadcast packet is set from within an OLSR network, it will
normally leave the sending node via one of its 'normal' network interfaces
(like eth0, eth1), not via the 'bmf' network interface (bmf0). Packets going
out via bmf0 are captured, encapsulated and forwarded over the network

However, packets going out via any other interface than bmf0 are not
captured. By setting the plugin parameter "CapturePacketsOnOlsrInterfaces"
to "yes", the 'normal' network interfaces are put in promiscuous mode. I
assumed that outgoing packets would be captured on interfaces in promiscuous
mode, but it appears that this is not the case. Only incoming packets are

Normally this would not be a problem, since any IP local broadcast packet
sent from an OLSR-enabled network interface will be received by at least one
OLSR neighbor node. For that neighbor node, the packet will be an incoming
packet, which is correctly captured, so it can be encapsulated and forwarded
over the network. The problem occurs when the capturing node is not an MPR
for the sending node. The forwarding algorithm will then decide not to
forward the packet. If the capturing node happens to be the only node that
receives the packet, that means the end of the forwarding.

So, the challenge is now to update the forwarding algorithm somewhat, in
such a way that unencapsulated packets received on an OLSR-enabled network
interface are forwarded, even on a node that is not an MPR for sending node.

Even better: find a way to capture outgoing (broadcast) packets on a
'normal' network interface. Do you have any ideas?



-----Oorspronkelijk bericht-----
Van: ZioPRoTo (Saverio Proto) [mailto:(spam-protected)] 
Verzonden: donderdag 17 maart 2011 20:13
Aan: Erik Tromp
CC: Vincent Nuttin; olsr-dev
Onderwerp: Re: [Olsr-dev] olsrd + bmf plugin

> Finally, I discovered there is a bug in BMF regarding the use of IP 
> local
> broadcast: it appears that IP local broadcast packets captured on an 
> OLSR-enabled network interface are not always forwarded where they 
> should be. This happens on nodes which have not been selected as an 
> MPR. A little technical... but I am currently trying to create a fix for

do you think that this bug could be inherited also to mDNS and p2p plugins
of olsrd ? Because we both started from the BMF codebase ! :)


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