From: Theo Buehler <tb@theobuehler.org>
Subject: Re: do not add default routes with blackhole or reject to the egress group
To: tech@openbsd.org
Date: Wed, 14 May 2025 08:29:03 +0200

On Wed, May 14, 2025 at 08:22:07AM +0200, Claudio Jeker wrote:
> On Wed, May 14, 2025 at 07:11:04AM +0100, Jason McIntyre wrote:
> > On Wed, May 14, 2025 at 08:06:28AM +0200, Claudio Jeker wrote:
> > > On Wed, May 14, 2025 at 06:50:13AM +0100, Jason McIntyre wrote:
> > > > On Wed, May 14, 2025 at 01:54:42AM +0200, Micha?? Markowski wrote:
> > > > > czw., 1 maj 2025 o 20:52 Micha?? Markowski <markowski1@gmail.com> napisa??(a):
> > > > > > Maybe this should be mentioned explicitly in ifconfig(8).
> > > > > >
> > > > > > --- sbin/ifconfig/ifconfig.8
> > > > > > +++ sbin/ifconfig/ifconfig.8
> > > > > > @@ -247,7 +247,11 @@ interface group.
> > > > > >  .It
> > > > > >  The interfaces the default routes point to are members of the
> > > > > >  .Dq egress
> > > > > > -interface group.
> > > > > > +interface group, except for the ones marked with
> > > > > > +.Fl blackhole
> > > > > > +or
> > > > > > +.Fl reject
> > > > > > +flag.
> > > > > >  .It
> > > > > >  IEEE 802.11 wireless interfaces are members of the
> > > > > >  .Dq wlan
> > > > > 
> > > > > Any thoughts on this?
> > > > > 
> > > > 
> > > > i don;t understand it myself - don;t these flags apply to routes, rather
> > > > than interfaces?
> > > 
> > > The problem is that 'the ones' in the text above refers to routes and not
> > > the interfaces. Interfaces are added to the egress group if a usable
> > > default route uses that interface to send traffic out.  This now excludes
> > > blackhole and reject routes (a change made not that long ago).
> > > 
> > > > having said that, for your language i suggest either
> > > > 
> > > > 	marked with *the* -blackhole or -reject flag.
> > > > or
> > > > 	marked with -blackhole or -reject.
> > > > 
> > > > jmc
> > > > 
> > > 
> > > -- 
> > > :wq Claudio
> > > 
> > 
> > right, meaning that an interface can have blackhole or reject set on a
> > route, and still have a usable default route marked "egress".
> > 
> > i.e. the diff is not correct?
> 
> Yes, in theory that is possible but not very likely.
> 
> -reject and -blackhole routes must use lo(4) as interface. I think we tell
> people to use 127.0.0.1 as nexthop for those routes. 
> 
> You need to add routes at different priority to have multiple default
> routes over the same interface.
> 
> So something like:
> route add default -priority 56 -blackhole 127.0.0.1
> route add default -priority 8 127.0.0.1
> 
> Would mark lo0 as egress but the -blackhole route will never match since
> it is fully covered by the higher priority (8) route.
> 
> Side note:
> In general using egress in pf.conf nat-to rules is tricky if there are
> multiple default routes on the system. E.g. if you have wired and wireless
> and umb all active at once. The nat-to rule may select the wrong address
> for outgoing traffic.

Does this work? I dropped the inline Xr since it always became awkward.

Index: ifconfig.8
===================================================================
RCS file: /cvs/src/sbin/ifconfig/ifconfig.8,v
diff -u -p -r1.404 ifconfig.8
--- ifconfig.8	13 May 2025 15:11:54 -0000	1.404
+++ ifconfig.8	14 May 2025 06:28:44 -0000
@@ -231,9 +231,8 @@ Some interfaces belong to specific group
 .It Cm all
 All interfaces.
 .It Cm egress
-Any interfaces in the default
-.Xr rdomain 4
-to which default routes point to.
+All interfaces to which default routes point that are in rdomain 0
+but not blackhole or reject routes.
 .It Cm netboot
 Any interfaces used for network booting, e.g. via
 .Xr pxeboot 8 .
@@ -2480,6 +2479,7 @@ tried to alter an interface's configurat
 .Xr inet 4 ,
 .Xr intro 4 ,
 .Xr netintro 4 ,
+.Xr rdomain 4 ,
 .Xr rtable 4 ,
 .Xr hostname.if 5 ,
 .Xr hosts 5 ,