[Olsr-dev] Good ideas about interface IPs in OLSR

Henning Rogge (spam-protected)
Thu Feb 5 17:38:48 CET 2009

Hello everybody,

we had some interesting talks about the evil "all interfaces same IP" thing on 
the funkfeuer list, so I would like to present the result of this 
brainstorming to talk about it with the whole olsr-dev community.

Just to state the problem:
There seem to be a growing number of people who configure multiple (sometimes 
all) interfaces to the same IP. This introduces a number of problems with 
OLSR, especially with the strange 1-hop neighbor topologies you can create 
with WLAN.

Two important reasons why people do this is
1.) to save IPs
2.) to make sure that the main-ip of OLSR does not change.

We want to get away from this configuration (it create headaches for OLSR 
programmers ^^), so we are working on technical sollutions for this.

Two parts of the sollution are already in the development repository:
1.) there is a configuration option to set the main-ip to a fixed value
2.) there is a configuration option to set the type of the interface. At the 
moment you can choose "mesh" (default value) or "ethernet"...

The "ethernet" settings tells OLSR that this interface has no real loss on 
it's broadcast domain (either anyone gets it or noone gets it), so it does not 
need to retransmit OLSR packages received from this interface back into the 
interface again.

Another part of the puzzle is the idea to set the source address of all routes 
to the main IP. This way any package created on the router will have the main-
IP of the router as the source field. It needs some additional work, but 
Markus Kittenberg is already working on it.

Another thing I plan to work on in March (will be busy with other stuff this 
month) is the "virtual OLSR mode". By declaring all connected OLSR instances 
on an interface "virtual" you tell them they are really just ONE OLSR node 
distributed among a few hardware nodes (Foneras, Linksys-Boxes, ect.). The 
boxes will discover each other automatically and will behave as one. This will 
reduce the number of TCs we have in our larger networks by a factor of 2 or 
even 3 !

But back to the "same IP" stuff...
In my oppinion it would be the best to block same IPs on OLSR interfaces at 
all, but there seems to be opposition to this. So the idea developed on the 
Funkfeuer list is to allow same IPs on "ethernet" interfaces, but not on 
normal mesh interfaces. You will get only a warning for ethernet, but an ERROR 
for mesh interfaces.

We don't plan to include this block into version 0.5.7, but I would like to 
include it into 0.6.0 (we have to talk about this in the dev group), so there 
is plenty of time to work on the IP configuration.

In the end (which might be a year away or more) it would be nice to reduce the 
importance of the interface IPs even more, so that we can switch to link-local 
(autoconfigured !) addresses in IPv6. 

Comments ? Cries ? Instant demonstrations ? ;)


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