[OLSR-users] When does a node use ARP?

Henning Wangerin (spam-protected)
Sat Jul 8 22:47:46 CEST 2006

On Sun, 2006-07-09 at 01:16 +1000, Dan Flett wrote:
> I am wondering - can an OLSR node communicate with a one-hop non-OLSR node
> if there is a HNA present with a netmask that overlaps the non-OLSR node?

Yes, and no HNA is needed if communication is needed when the boxes can
hear them.

I have a WLAN-ip-camera setup with a a.b.c.d/24 address connecting to
one of my nodes at a.b.c.1/16 olsr-network.

If I nedd to be able to contact the camera from elsewhere the camrea
need to be setup with standard gateway to a.b.c.1 _and_ a HNA entry to
a.b.c.d, otherwise the will be do routes to/from the camera.

> Consider this scenario:
> Node A has a wireless interface with the IP address and is
> running OLSR
> Node Z is running OLSR and is injecting a HNA of onto the
> network and is many hops away from Node A
> Node B is has a wireless interface with the IP address of and
> is within radio range (and therefore Ethernet range), of Node A but does not
> run OLSR.
> My question is - If Node A, with an empty ARP cache, attempts to communicate
> with Node B - what happens?  Normally Node A would send an ARP broadcast and
> Node B would answer it.  But does the /17 HNA from Node Z interfere with
> this?  Would Node A consult it's routing table and decide that the traffic
> should go via Node Z, unaware that Node B is within direct Ethernet range?

If there is a route to some IP no arp-request will be sent, as
(logically) the route is already known.

Mixing olsr-nodes and non-olsr-nodes is a real mess.

Especially if the non-olsr-node is expected to do some routing. Again it
can be done by using static routes on (all) the neightbourghs, but it
defeats the automatic route-creation done but olsr.

In my world, I'd only allow end-nodes to be non-olsr, as in my setup
with the camera mentioned above. Under no circumstances would I use
non-olsr-nodes as routers.

I'd doing some experiments with openvpn to connect olsr-islands
together vis open vpn, but all nodes will still be logically routed on
the same 10.128.x.y/16 network. Some WLAN, some ethernet and som

Henning Wangerin <(spam-protected)>

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