netdev - Re: Maybe a bug with adding default routes?

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Message-ID: <CAPzBOBOaTJ8y+CEL6Mvy1qORWRWVVeKnATA=fxeG+=+gFMNC3w@mail.gmail.com>
Date:   Wed, 19 Apr 2023 12:20:06 +0200
From:   Robert Landers <landers.robert@...il.com>
To:     Toke Høiland-Jørgensen <toke@...nel.org>
Cc:     netdev@...r.kernel.org
Subject: Re: Maybe a bug with adding default routes?

On Wed, Apr 19, 2023 at 11:51 AM Toke Høiland-Jørgensen <toke@...nel.org> wrote:
>
> Robert Landers <landers.robert@...il.com> writes:
>
> > Hello netdev,
> >
> > I believe I either found a bug, or I'm doing something wrong (probably
> > the latter, or both!). I was experimenting with getting a "floating
> > IP" for my home lab, and eventually, I got it to work, but it requires
> > some voodoo, which intrigued me and I think I found some strange
> > behavior that smells like a bug. I'm on Ubuntu 22.04 (and Pop OS! on
> > my desktop), so it is also possible that this is fixed upstream (in
> > which case, I'll email that list next).
> >
> > To reproduce is quite simple:
> >
> > echo "1234 test" >> /etc/iproute2/rt_tables
> > ip route add default via 167.235.212.73 dev enp9s0 table test
> >
> > This will fail with the error:
> >
> > Error: Nexthop has invalid gateway.
> >
> > Now, I think this makes sense, however, the routing table shouldn't
> > need to know about hops, Right? Maybe I'm wrong, but this voodoo
> > results in a correct routing table:
> >
> > ip addr add 167.235.212.72/29 dev enp9s0
> > ip route add default via 167.235.212.73 dev enp9s0 table test
> > ip addr del 167.235.212.72/29 dev enp9s0
> >
> > I'm not sure if this is a bug or working as designed. It smells like a
> > bug, but I could just as easily be doing something wrong. I grew up in
> > "simpler" times and am not nearly as familiar with iproute2 as I was
> > with the old stuff.
>
> Try the 'onlink' flag:
>
> ip route add default via 167.235.212.73 dev enp9s0 onlink table test
>
> -Toke

Hello Toke,

I tried onlink but it did not work; packets appeared to never leave the device.