misleading documentation for the "direct" protocol

[Maria Matejka]

Hello Lexi!

(Explicit Cc to David)

On Sun, May 31, 2026 at 10:57:54PM +0100, Lexi Winter wrote:

> the BIRD documentation says for the "direct" protocol[0]:
> 
> > The question is whether it is a good idea to have such device routes
> > in BIRD routing table. OS kernel usually handles device routes for
> > directly connected networks by itself so we don't need (and don't
> > want) to export these routes to the kernel protocol. OSPF protocol
> > creates device routes for its interfaces itself and BGP protocol is
> > usually used for exporting aggregate routes. But the Direct protocol
> > is necessary for distance-vector protocols like RIP or Babel to
> > announce local networks. 
> 
> [0] https://bird.network.cz/?get_doc&v=30&f=bird-6.html#ss6.7

This has not changed for a long time and the new versions have the same
text but just for the record, we changed websites and we're still
failing to setup redirects from the old one.

→ https://bird.nic.cz/doc/bird-3.3.0.html#direct

> as i read this, it is suggesting that if BIRD is only running OSPF, then
> the "direct" protocol is not needed.  however, i've tested this and i'm
> not sure it's true.

I'm quite sure it's true for both Linux and BSD.

> without direct, and with a basic OSPF configuration with no peers, BIRD
> will flag the OSPF interface routes with '!':
> 
> 	root at witch:/usr/local/etc # birdc show route
> 	BIRD 3.2.0 ready.
> 	Table master4:
> 	81.2.96.160/28       unicast [core4 22:45:00.630] ! I (150/10) [198.18.2.4]
> 		dev genet0
> 
> 	Table master6:
> 	2001:8b0:aab5:c401::/64 unicast [core6 22:45:00.630] ! I (150/10) [198.18.2.4]
> 		dev genet0
> 
> it will also log very much some netlink errors:
> 
> May 31 22:51:04 witch bird[31390]: Netlink: File exists
> May 31 22:51:04 witch syslogd: last message repeated 1 times
> May 31 22:52:04 witch bird[31390]: Netlink: Address already in use
> May 31 22:52:04 witch bird[31390]: Netlink: File exists
> May 31 22:52:04 witch syslogd: last message repeated 1 times

This looks like a kernel protocol bug. If you are, by any chance, able
to describe to us the interface configuration and BIRD configuration,
we'd be very pleased so that we don't have to try _something_. You may
send this off-list of course.

> the OSPF interface routes are correctly installed (or rather, not installed,
> since the kernel already installed them):
> 
> 	root at witch:/usr/local/etc # birdc show route
> 	BIRD 3.2.0 ready.
> 	Table master4:
> 	81.2.96.160/28       unicast [direct1 22:53:29.436] * (240)
> 		dev genet0
> 			     unicast [core4 22:53:29.529] I (150/10) [198.18.2.4]
> 		dev genet0
> 
> 	Table master6:
> 	2001:8b0:aab5:c401::/64 unicast [direct1 22:53:29.436] * (240)
> 		dev genet0
> 			     unicast [core6 22:53:29.529] I (150/10) [198.18.2.4]
> 		dev genet0

This is very weird.

> and BIRD does not log anymore the netlink-related errors.

This is even more weird.

> i tested this on FreeBSD 15.0, so possibly this is a FreeBSD-specific
> behaviour that isn't present on Linux; i don't have any Linux systems
> to test with.  but, i think the documentation of the "direct" protocol
> could be changed to indicate that configuring it may be necessary in
> at least some situations.

We'll try this on FreeBSD 15.0 and see what happens. Thank you for
reporting this!

-- 
Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.  
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