Injecting OSPF learned routes (only)

[Alexander Zubkov]

Hi all,

Maybe it can be solved by having those kernel routes in the bird
itself? So that it knows about them and choose them as the "best". In
that case it will not reexport them back to the kernel. Recent
addition of "learn all" option to kernel protocol should be helpful
here. Haven't tried such solution myself, though.

Regards,
Alexander

On Tue, Feb 27, 2024 at 9:10 AM ico <ico at petrzalka.net> wrote:
>
> Hello Nico,
>
> I wrestled with this too. The reason you see those routes is this: If
> you configure an interface in OSPF, OSPF uses its own mechanism for
> learning link routes (direct routes?) from kernel. Those routes get into
> some bird's routing table together with all other routes from OSPF. And
> everything is exported into kernel.
>
> So my solution is to use differences between routes learned from
> neighbors and local link routes: link routes don't have a gateway.
> So I filter out all routes without gateway in export filter like this:
>
> protocol kernel krnl4 {
>      ipv4 {
>          export filter {
>              # export to kernel only routes with gateway
>              if gw.mask(0) = 0.0.0.0 then accept;
>              reject;
>          };
>          import filter {
>              # no default gw from kernel, want default gw from ospf
>              if net = 0.0.0.0/0 then reject;
>              accept;
>          };
>      };
>      learn;
> }
>
> I don't know how to filter routes with a gateway properly, but
> "gw.mask(0) = 0.0.0.0" works for me. Maybe there is some better way to
> do this?
>
> I hope this helps you.
>
> ico
>
> On 27. 2. 2024 4:30, Nico Schottelius via Bird-users wrote:
> >
> > Good morning bird users,
> >
> > I am a bit puzzled about properly adding OSPF learned routes into the
> > kernel and let me show you why:
> >
> > If I use a filter such as:
> >
> > filter static_and_bgp_and_ospf {
> >    if(source = RTS_STATIC || source = RTS_BGP || source = RTS_OSPF) then accept;
> >    reject;
> > }
> >
> > And configure the kernel to use it like this:
> >
> > protocol kernel kernel_v4 {
> >          ipv4 { export filter static_and_bgp_and_ospf; };
> > }
> >
> > protocol kernel kernel_v6 {
> >          ipv6 { export filter static_and_bgp_and_ospf; };
> > }
> >
> >
> > Then I get route duplications in the kernel:
> >
> > [04:29] server123.place10:~# ip r | grep 147.78.195.224/27
> > 147.78.195.224/27 dev eth1 proto kernel scope link src 147.78.195.254
> > 147.78.195.224/27 dev eth1 proto bird scope link metric 32
> >
> > The reason for that semes:
> >
> > - server123 has the route because of an interface address
> > - other hosts in the network also have an interface in that network
> >
> > While this is not necessarily a big problem, it seems wrong to inject
> > the route, because we learned it from OSPF, even though we already had
> > it in the first place.
> >
> > How do you usually handle inserting OSPF learned routes? Do you just
> > have them duplicate or do you have some logic that resembles..
> >
> >       "If I already have that route and I receive it again from outside
> >        (such as OSPF), do not inject it again"
> >
> > ?
> >
> > Looking forward to read how you handle this logic!
> >
> > Best regards from Seoul,
> >
> > Nico
> >
> > --
> > Sustainable and modern Infrastructures by ungleich.ch