[OLSR-users] Problems when losing one link in a dual link setup

Roar Bjørgum Rotvik (spam-protected)
Wed Feb 9 16:17:15 CET 2005

Andreas Tønnesen wrote:
> We have done some bugfixes regarding route addition/deletion now.
> Could you try the CVS version on you scenario?

Hello again Andreas,

Today I testet my setup with the current CVS-version.

(I created an RPM-package for today CVS-version if anybody is interested..)

Now the setup with two links between olsrd-nodes worked a lot better. 
When unplugging the ethernet, the WLAN link took over and traffic resumed.

But it took 15 seconds from the cable was unplugged to the traffic 
resumed over WLAN, even if WLAN connection was still working all the time.

The reason for this is that when the eth0 (LAN, default interface) is up 
an running alongside with eth1 (WLAN), a routing entry for the other 
node WLAN IP ( is added with interface eth0 in the routing 
table. So all traffic to the WLAN interface is routed over the LAN 
interface. This is ok in normal operation.

But when LAN is down, I think OLSRD should change the route for to use interface eth1 as soon as possible, but I guess that 
OLSRD need to wait for 3 lost HELLO packets before the link is 
determined to be down and may recalculate the routing tables?
In this special case it should perhaps be possible for olsrd to detect 
that the cable is unplugged right away, but that would not help if both 
interfaces is WLAN..

I also saw some inconsistencies in what interface was used as default.
a) When starting olsrd on two nodes with WLAN connected and LAN cable 
disconnected, eth1 (WLAN) was used as interface for both LAN and WLAN IP 
addresses for the other node.
eth0 (LAN) was configured to be the main interface on both nodes.

b) When inserting the LAN cable, WLAN interface was still used.
I had hoped that olsrd would change to LAN interface as it is configured 
as main interface (I thought I saw this one time, but are not sure).

c) When starting olsrd with WLAN and LAN connected, LAN was used as main 
interface until cable disconnect and switch to WLAN interface (after 
15sec as noted above). When connecting the LAN cable again, sometimes 
the LAN interface was selected as default interface, sometimes WLAN was 
still used.

I'll do some more testing with traces to verify this issue when I got 
the time.


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