Linux 3.9 routing oddity

Emmanuel Thierry ml at
Wed Jul 3 10:43:47 CEST 2013


Le 3 juil. 2013 à 10:31, Benedikt Stockebrand a écrit :

> Hi Gert, Pierre, and list,
> Gert Doering <gert at> writes:
>> Hi,
>> On Tue, Jul 02, 2013 at 10:09:00PM +0200, Jeroen Massar wrote:
>>> You might also want to try this out with something that is not a tun/tap
>>> interface, thus a default ethernet interface, as tun/tap might have all
>>> kinds of odd behavior, eg no or hacked neighbor discovery depending on
>>> the tool being used by the tun device. (and in case you use openvpn,
>>> kick Gert ;)
>> I'm not sure why it would want to use ND on a tun device anyway...  it
>> doesn't do that for mine.
> maybe I'm too low on caffeine right now, but doesn't the loop prevention
> on a point-to-point interface use ND when a subnet prefix (rather than
> two unrelated IP addresses with an interface route) is configured for
> that link?

It uses ND to perform the DAD (so with its own address) when the subnet is configured but i'm not sure it is not supposed to check that the gateway exists at the moment the route is added.
By the way i cross-tested it with a basic setup using two virtual hosts, the problem occurs on 3.9 kernels, not on 3.8.

Best regards.
Emmanuel Thierry

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