Fw: [Bug 206523] New: Can no longer add routes while the link is down, RTNETLINK answers: Network is down

Fw: [Bug 206523] New: Can no longer add routes while the link is down, RTNETLINK answers: Network is down

[Stephen Hemminger]

Begin forwarded message:

Date: Thu, 13 Feb 2020 18:04:40 +0000
From: bugzilla-daemon@bugzilla.kernel.org
To: stephen@networkplumber.org
Subject: [Bug 206523] New: Can no longer add routes while the link is down, RTNETLINK answers: Network is down


https://bugzilla.kernel.org/show_bug.cgi?id=206523

            Bug ID: 206523
           Summary: Can no longer add routes while the link is down,
                    RTNETLINK answers: Network is down
           Product: Networking
           Version: 2.5
    Kernel Version: 5.4.19
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Other
          Assignee: stephen@networkplumber.org
          Reporter: rm+bko@romanrm.net
        Regression: No

Hello,

I'm upgrading my machines from kernel 4.14 to the 5.4 series, and noticed quite
a significant behavior change, so I was wondering if this was intentional or a
side effect of something, or a bug. It already broke my network connectivity
for a while and required troubleshooting, to figure out that a certain script
that I had, used to set up all routes before, and only then putting the
interface up.

On 4.14.170 this works:

# ip link add dummy100 type dummy
# ip route add fd99::/128 dev dummy100
# ip -6 route | grep dummy
fd99:: dev dummy100 metric 1024 linkdown  pref medium
#

On 5.4.19 however:

# ip link add dummy100 type dummy
# ip route add fd99::/128 dev dummy100
RTNETLINK answers: Network is down
# ip -6 route | grep dummy
#

Sorry for not narrowing it down more precisely between 4.14 and 5.4, but I'm
sure for the right people this will be easily either an "oh shit" or "yeah,
that", even without any more precise version information :)

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Re: Fw: [Bug 206523] New: Can no longer add routes while the link is down, RTNETLINK answers: Network is down

[Ido Schimmel]

On Sun, Feb 16, 2020 at 09:43:07AM -0800, Stephen Hemminger wrote:
> 
> 
> Begin forwarded message:
> 
> Date: Thu, 13 Feb 2020 18:04:40 +0000
> From: bugzilla-daemon@bugzilla.kernel.org
> To: stephen@networkplumber.org
> Subject: [Bug 206523] New: Can no longer add routes while the link is down, RTNETLINK answers: Network is down
> 
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=206523
> 
>             Bug ID: 206523
>            Summary: Can no longer add routes while the link is down,
>                     RTNETLINK answers: Network is down
>            Product: Networking
>            Version: 2.5
>     Kernel Version: 5.4.19
>           Hardware: All
>                 OS: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: Other
>           Assignee: stephen@networkplumber.org
>           Reporter: rm+bko@romanrm.net
>         Regression: No
> 
> Hello,
> 
> I'm upgrading my machines from kernel 4.14 to the 5.4 series, and noticed quite
> a significant behavior change, so I was wondering if this was intentional or a
> side effect of something, or a bug. It already broke my network connectivity
> for a while and required troubleshooting, to figure out that a certain script
> that I had, used to set up all routes before, and only then putting the
> interface up.
> 
> On 4.14.170 this works:
> 
> # ip link add dummy100 type dummy
> # ip route add fd99::/128 dev dummy100
> # ip -6 route | grep dummy
> fd99:: dev dummy100 metric 1024 linkdown  pref medium
> #
> 
> On 5.4.19 however:
> 
> # ip link add dummy100 type dummy
> # ip route add fd99::/128 dev dummy100
> RTNETLINK answers: Network is down
> # ip -6 route | grep dummy
> #
> 
> Sorry for not narrowing it down more precisely between 4.14 and 5.4, but I'm
> sure for the right people this will be easily either an "oh shit" or "yeah,
> that", even without any more precise version information :)

Hi,

This was added over two years ago in commit 955ec4cb3b54 ("net/ipv6: Do
not allow route add with a device that is down"), kernel 4.16

With recent iproute2 you can get extended ack from the kernel:
# ip route add fd99::/128 dev dummy10
Error: Nexthop device is not up.

IMO, it's better to keep it consistent with IPv4. We can also add a
sysctl, but I would like to avoid it if possible.

Adding David in case he has other suggestions.