[Olsr-users] Two ethernet links to the same host makes things get worst

Ferry Huberts (spam-protected)
Tue Jan 6 09:03:09 CET 2015

On 06/01/15 01:00, Michael Rack wrote:
>> These kinds of links should be configured as bonded links or teamed
>> interfaces. Running olsrd on them, especially with the same IP, is not
>> such a good idea.
>> The same IP on multiple interfaces is not such a good idea either way.
> I know that this configuration is not standard and many systems as
> Vayetta or CISCO prevent users to assign the same ip-address to multiple
> interfaces but i think there is no problem in using this configuration
> because the IP-Layer supports this without a shame.

There is a difference between allowing something and things working as 
you expect.

This is Linux, if you want to shoot yourself in the foot, then go ahead...

The same IP on an interface - at the very least - is very confusing and 
asking for trouble. The kernel can the pick any interface it likes to 
route traffic over. If at one point the kernel's interface data 
structures get
reordered, a different interface and - at the very least - the 
connection tracking and firewalling will break. Routing will be 
confused, connections break, etc etc.
Also, most programs assume that you don't do this and will therefore 
also break in unexpected and mostly unpleasant ways.

Summary: avoid doing this if at all possible.

> Now it is 00:53am and my clients are in sleep, so i could test the
> arprefresh plugin and it looks as it does the trick.
>> # arp -an | grep '2220'
>> ? ( at 24:a4:3c:b3:db:99 [ether] on eth0.2220
>> # arp -an | grep '2221'
>> ? ( at 24:a4:3c:b3:db:9a [ether] on eth1.2221
> this looks good and the link works as expected. I hope that my issue is
> solved, otherwise i will report any problems to the list.
> PS: Bridging is not a real solution because i have to enable STP. There
> are many switches attachted to the fiber-link #2, so without STP i will
> get a packetloop, but with STP i am not aware, how the routing is
> currently arranged.

Ferry Huberts

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