[Olsr-users] MPR Selection problem

Henning Rogge (spam-protected)
Sat Oct 25 09:45:53 CEST 2014

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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