bird 2.0.3 does not install multipath route in kernel

[Joakim Tjernlund]

On Fri, 2019-03-01 at 12:41 +0100, Ondrej Zajicek wrote:
> 
> 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.

Quagga somehow detects this and will install one route into kernel and keep the other
as an inactive standby route. Maybe Bird could do the same ?

 Jocke