netdev - Re: [BUG] Dependence of routing cache entries on the ignore-df flag

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Date: Fri, 5 May 2023 08:00:14 -0700
From: Stephen Hemminger <stephen@...workplumber.org>
To: David Ahern <dsahern@...nel.org>
Cc: Aleksey Shumnik <ashumnik9@...il.com>, netdev@...r.kernel.org,
 waltje@...lt.nl.mugnet.org, Jakub Kicinski <kuba@...nel.org>,
 gw4pts@...pts.ampr.org, kuznet@....inr.ac.ru,
 "willemdebruijn.kernel@...il.com" <willemdebruijn.kernel@...il.com>,
 gnault@...hat.com
Subject: Re: [BUG] Dependence of routing cache entries on the ignore-df flag

On Thu, 4 May 2023 21:10:43 -0600
David Ahern <dsahern@...nel.org> wrote:

> On Wed, May 03, 2023 at 11:35:28AM -0700, Stephen Hemminger wrote:
> > On Wed, 3 May 2023 18:01:03 +0300
> > Aleksey Shumnik <ashumnik9@...il.com> wrote:
> >   
> > > Might you answer the questions:
> > > 1. How the ignore-df flag and adding entries to the routing cache is
> > > connected? In which kernel files may I look to find this connection?
> > > 2. Is this behavior wrong?
> > > 3. Is there any way to completely disable the use of the routing
> > > cache? (as far as I understand, it used to be possible to set the
> > > rhash_entries parameter to 0, but now there is no such parameter)
> > > 4. Why is an entry added to the routing cache if a suitable entry was
> > > eventually found in the arp table (it is added directly, without being
> > > temporarily added to the routing table)?  
> > 
> > What kernel version. The route cache has been completely removed from
> > the kernel for a long time.  
> 
> These are exceptions (fib_nh_exception), not the legacy routing cache.

I tried to reproduce your example, and did not see anything.
Could it be the multicast routing daemon (pimd) is watching and adding
the entry?