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Message-ID: <55C4D803.3090108@redhat.com>
Date: Fri, 07 Aug 2015 09:08:35 -0700
From: Alexander Duyck <alexander.h.duyck@...hat.com>
To: Zang MingJie <zealot0630@...il.com>
CC: Alexander Duyck <alexander.duyck@...il.com>,
Daniel Borkmann <daniel@...earbox.net>,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
Stephen Hemminger <stephen@...workplumber.org>,
David Miller <davem@...emloft.net>
Subject: Re: [BUG] net/ipv4: inconsistent routing table
On 08/07/2015 01:23 AM, Zang MingJie wrote:
> IMO, the routing decision is determined, given a specific routing
> table and local network the result MUST be determined, independence of
> how/what order the routing entry is added.
>
> Now there are two ways to configure the system resulting EXACTLY the
> same routing table and local addresses, but the routing decision is
> totally different.
>
> SAME routing table, DIFFERENT routing decision, there MUST be bugs in kernel
I wasn't arguing that the behavior is undesirable, but the likelihood of
having a default route assigned to a local address should be pretty
low. If the system is the default route of others then it should have a
different default gateway than itself. For example an office router
would end up pointing to the ISP as the gateway, and the ISP would
either point to some other provider or run a BGP configuration. So in
the case of the default route transitioning to us we should end up
having to delete and update the default route anyway. This is likely
one of the reasons why there hasn't been any issues reported with this
behavior until now.
I'm just wondering if the work involved to fix it is going to be worth
it. We have to keep in mind that this will result in a change of
behavior for existing users and we don't know if anyone might be
expecting this type of behavior.
We basically are looking at one of three options. The first one is to
just delete the route if you add the gateway as a local address or
remove it. That would be consistent with what you might see if the
address was the sole address on an interface of its own. The second
option is to update the nh_scope which I believe should be transitioned
between RT_SCOPE_HOST to RT_SCOPE_LINK if I am understanding things
correctly. The third option is we don't change the behavior and just
document it. This would then require manually deleting and restoring
any routes that use a recently modified address as their gateway.
Based on your feedback I'm assuming you would probably prefer the second
option. I'm just waiting to see if there are any other opinions on the
matter before I act.
Thanks.
- Alex
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