[Olsr-users] Why BMF is forwarding the multicast packets as unicast?

Erik Tromp (spam-protected)
Wed Oct 24 21:58:17 CEST 2007


The reason why BMF encapsulates traffic (sometimes) into unicast packets is
explained in the README_BMF.txt file, Chapter 10 (Version history):

31 Mar 2007: Version 1.4
* Optimized the standard forwarding mechanism such that, if the network
  topology indicates there is only one neighbor on an interface, packets are
  sent to the specific IP address (unicast) of that neighbor. If the network
  topology indicates there are multiple neighbors, then BMF will still send
  packets to the IP local-broadcast address.  

About your other issue:

Normally you should set the PlParam "CapturePacketsOnOlsrInterfaces"
to "no" (or: leave it to its default value of "no" by not mentioning this
line in the config). You only set the PlParam
to "yes" if there is a specific application that does not use the
routing table to determine via which network interface to send its multicast
packets. As BMF automatically sets the routing table to forward all
packets via the virtual network interface "bmf0", these packets will be
normally be forwarded by BMF without the need for promiscuously capturing
them off another network interface.

See also Chapter 6 (Advanced configuration) of the README_BMF.txt file,
under the heading 'CapturePacketsOnOlsrInterfaces'.

In other words: RT*M :-))

Best regards,

-----Oorspronkelijk bericht-----
Van: (spam-protected)
[mailto:(spam-protected)] Namens (spam-protected)
Verzonden: dinsdag 23 oktober 2007 18:58
Aan: olsr-users
Onderwerp: [Olsr-users] Why BMF is forwarding the multicast packets as


The scenario consists of two nodes working in ad-hoc mode with each node
running olsr v-0.5.3 and BMf plugin 1.5.1. In my case, If Node A generates
the multicast traffic with MGEN then instead of receiving the multicast
packtes the Node B receives the unicast packtes and it ackknowledges the
individual packtes as well. I am using as the multicast address.

This behavior has been observed by capturing the packets on Node B using
WireShark and even by sniffing the 802.11 traffic and each packet has its
src.addr [Node A] and dest.adr [Node B] --> not

Ok, the same is true if the ad hoc network consist of three nodes with
olsr-bmf running.

I have the following lines for the OLSR-BMF,

   LoadPlugin "olsrd_bmf.so.1.5"
       PlParam "BmfInterface" "bmf0"
	PlParam "CapturePacketsOnOOlsrInterfaces" "yes"

Curious to know the reason.

Best wishes,

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