[Olsr-users] MPR Selection problem

Scoobi Doo (spam-protected)
Sat Oct 25 18:55:23 CEST 2014

Yes, the default MTU is 1500. AFAIK i don't think that i have made a mistake since the packets are fragmented according to this MTU. Furthermore, without  ETX it works well.  
My suspicion is that when hello packets are fragmented it is somehow affect the etx calculation. what do you think?

On Saturday, October 25, 2014 10:45 AM, Henning Rogge <(spam-protected)> wrote:

So you modified the code in olsrd to somehow keep the MTU smaller than
it really is? Maybe you forgot one place?


On Fri, Oct 24, 2014 at 4:17 PM, Scoobi Doo <(spam-protected)> wrote:
> The MTU limit is on the olsr packet not on the whole IP packet. the total
> packet size is 128 + udp headers + IP headers. It's still a standard IPv4
> packet with just a small payload - olsr packet.
> On Friday, October 24, 2014 2:54 PM, Henning Rogge <(spam-protected)> wrote:
> On Fri, Oct 24, 2014 at 1:30 PM, Scoobi Doo <(spam-protected)> wrote:
>> Hi,
>> Your answer regarding using ETX code brings me back to another problem. I
>> don't use ETX because i'm having simulations on narrowband nodes, which
>> force me to change the size of the MTU (from 1500 to 128).
> Not sure an IP (especially IPv6) network with MTU 128 does work
> well... you might need to think about layer-2 fragmentation.
>>When the network
>> gets larger and the olsrd starts to fragment the messages (serialize
>> functions) the routing table in ETX-mode is not correct in a simple
>> full-mesh topology. From tests that i ran i saw that no matter what is the
>> MTU size whenever the network becomes larger so messages get fragmented,
>> the
>> olsrd fails to build the right routing table. When i use non-ETX code i
>> don't see that problem.
>> I prefer using ETX. did you encounter in such a problem?
> Most likely there is an "off by X" problem in the fragmentation
> code... it most likely doesn't trigger on IPv4 because messages stay
> small enough.
> Henning Rogge
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