netdev - Re: [PATCH] selftests: net: fib-onlink-tests: Set high metric for default IPv6 route

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Message-ID: <9a3f7b60-37e3-470e-b9f7-8cda5ddccb59@suse.de>
Date: Fri, 19 Dec 2025 15:51:50 +0100
From: Fernando Fernandez Mancera <fmancera@...e.de>
To: Ricardo B. Marlière <rbm@...e.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>, Shuah Khan <shuah@...nel.org>,
 David Ahern <dsahern@...il.com>
Cc: netdev@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests: net: fib-onlink-tests: Set high metric for
 default IPv6 route

On 12/18/25 1:20 PM, Ricardo B. Marlière wrote:
> Currently, the test breaks if the SUT already has a default route
> configured for IPv6. Fix by adding "metric 9999" to the `ip -6 ro add`
> command, so that multiple default routes can coexist.
> 
> Fixes: 4ed591c8ab44 ("net/ipv6: Allow onlink routes to have a device mismatch if it is the default route")
> Signed-off-by: Ricardo B. Marlière <rbm@...e.com>
> ---
>   tools/testing/selftests/net/fib-onlink-tests.sh | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/net/fib-onlink-tests.sh b/tools/testing/selftests/net/fib-onlink-tests.sh
> index ec2d6ceb1f08..acf6b0617373 100755
> --- a/tools/testing/selftests/net/fib-onlink-tests.sh
> +++ b/tools/testing/selftests/net/fib-onlink-tests.sh
> @@ -207,7 +207,7 @@ setup()
>   		ip -netns ${PEER_NS} addr add ${V6ADDRS[p${n}]}/64 dev ${NETIFS[p${n}]} nodad
>   	done
>   
> -	ip -6 ro add default via ${V6ADDRS[p3]/::[0-9]/::64}
> +	ip -6 ro add default via ${V6ADDRS[p3]/::[0-9]/::64} metric 9999
>   	ip -6 ro add table ${VRF_TABLE} default via ${V6ADDRS[p7]/::[0-9]/::64}
> 

It would probably require some work on the test but I think it could 
benefit from using two different network namespaces. Currently it is 
using PEER_NS and the default. I think avoiding the default one is 
beneficial for everyone as it ensures the state is clean and that the 
test won't interrupt the system connectivity.

Other tests already do that, e.g some tests in fib_tests.sh use ns1 and 
ns2 namespaces.

What do you all think?

>   	set +e
> 
> ---
> base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
> change-id: 20251218-rbm-selftests-net-fib-onlink-873ad01e6884
> 
> Best regards,