bird 2.0.3 does not install multipath route in kernel

[Kenth Eriksson]

On Fri, 2019-03-01 at 12:41 +0100, Ondrej Zajicek wrote:
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> On Fri, Mar 01, 2019 at 08:57:28AM +0000, Kenth Eriksson wrote:
> > > On Thu, Feb 28, 2019 at 01:15:02PM +0000, Kenth Eriksson wrote:
> > > > We have some multi-path routes that fails to get pushed into
> > > > the
> > > > kernel. We are running bird 2.0.3 and kernel 4.14.92+.
> > > > 
> > > > 
> > > > bird> show route
> > > > ...
> > > > Table master4:
> > > > 
> > > > 10.210.138.3/32      unicast [ospf1 13:24:23.022] E1 (145/1020)
> > > > [10.210.138.3]
> > > >       via 10.210.138.2 on p1-1-1-1-2 weight 1
> > > >       via 10.210.138.2 on p1-1-5-1-6 weight 1
> > > > ...
> > > > bird>
> > > 
> > > It is possible that it is related to the same IP address on
> > > different
> > > interfaces? Are these two interfaces to the same network?
> > > 
> > These are two unnumbered point-to-point interfaces.
> > 
> > We don't have multipath enabled in our kernel
> > (CONFIG_IP_ROUTE_MULTIPATH). How does bird tell whether the kernel
> > supports multipath? Probing run time via netlink? Didn't find any
> > configure.ac option.
> 
> BIRD does not detect that. I don't know if there is a reasonable way
> how to detect it. Just disable ECMP in OSPF if your kernel does not
> support ECMP routes.

Ok, thanks for clarifying that. The manual gave me the impression that
it was detected somehow since it has the following line:

"By default, ECMP is enabled if supported by Kernel"

> 
> > If disable multipath in the bird config like this;
> > 
> > protocol ospf v2 ospf1 {
> >     ecmp no;
> >     ...
> > 
> > then I could get bird to push one of the ospf multipath routes to
> > the
> > kernel again.
> 
> --
> Elen sila lumenn' omentielvo
> 
> Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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> "To err is human -- to blame it on a computer is even more so."