bird 2.0.3 does not install multipath route in kernel

[Kenth Eriksson]

On Fri, 2019-03-01 at 13:23 +0100, Ondrej Zajicek wrote:
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> On Fri, Mar 01, 2019 at 11:46:28AM +0000, Kenth Eriksson wrote:
> > > > 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"
> 
> OK, this is supposed to mean 'by Kernel protocol'. Kernel protocol
> supports ECMP on Linux, but not on BSD.
> 
I rebuilt my kernel with multipath support, that does seem to remove
the netlink warning logs. And now bird does push the prefix as a
multipath to the kernel.

Logs:

bird> show route for 172.20.4.41
Table master4:
172.20.4.41/32       unicast [ospf1 13:03:37.891] I (145/10)
[172.20.4.41]
	via 172.20.4.41 on p1-1-3-1-4 weight 1
	via 172.20.4.41 on p1-1-1-1-2 weight 1
                     unicast [direct1 13:43:08.338] (100)
	dev p1-1-1-1-2
                     unicast [direct1 13:43:08.338] (100)
	dev p1-1-3-1-4
bird>


kenth ~ # ip route
...
172.20.4.41  proto bird  metric 32 
	nexthop via 172.20.4.41  dev p1-1-1-1-2 weight 1
	nexthop via 172.20.4.41  dev p1-1-3-1-4 weight 1
kenth ~ # 



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