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Date:   Mon, 19 Oct 2020 20:57:31 -0600
From:   David Ahern <dsahern@...il.com>
To:     Vincent Bernat <vincent@...nat.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Corbet <corbet@....net>, netdev@...r.kernel.org,
        Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [PATCH net-next v1] net: evaluate
 net.conf.ipvX.all.ignore_routes_with_linkdown

[ fix Andy's address ]

On 10/17/20 6:50 AM, Vincent Bernat wrote:
> Introduced in 0eeb075fad73, the "ignore_routes_with_linkdown" sysctl
> ignores a route whose interface is down. It is provided as a
> per-interface sysctl. However, while a "all" variant is exposed, it
> was a noop since it was never evaluated. We use the usual "or" logic
> for this kind of sysctls.
> 
> Tested with:
> 
>     ip link add type veth # veth0 + veth1
>     ip link add type veth # veth1 + veth2
>     ip link set up dev veth0
>     ip link set up dev veth1 # link-status paired with veth0
>     ip link set up dev veth2
>     ip link set up dev veth3 # link-status paired with veth2
> 
>     # First available path
>     ip -4 addr add 203.0.113.${uts#H}/24 dev veth0
>     ip -6 addr add 2001:db8:1::${uts#H}/64 dev veth0
> 
>     # Second available path
>     ip -4 addr add 192.0.2.${uts#H}/24 dev veth2
>     ip -6 addr add 2001:db8:2::${uts#H}/64 dev veth2
> 
>     # More specific route through first path
>     ip -4 route add 198.51.100.0/25 via 203.0.113.254 # via veth0
>     ip -6 route add 2001:db8:3::/56 via 2001:db8:1::ff # via veth0
> 
>     # Less specific route through second path
>     ip -4 route add 198.51.100.0/24 via 192.0.2.254 # via veth2
>     ip -6 route add 2001:db8:3::/48 via 2001:db8:2::ff # via veth2
> 
>     # H1: enable on "all"
>     # H2: enable on "veth0"
>     for v in ipv4 ipv6; do
>       case $uts in
>         H1)
>           sysctl -qw net.${v}.conf.all.ignore_routes_with_linkdown=1
>           ;;
>         H2)
>           sysctl -qw net.${v}.conf.veth0.ignore_routes_with_linkdown=1
>           ;;
>       esac
>     done
> 
>     set -xe
>     # When veth0 is up, best route is through veth0
>     ip -o route get 198.51.100.1 | grep -Fw veth0
>     ip -o route get 2001:db8:3::1 | grep -Fw veth0
> 
>     # When veth0 is down, best route should be through veth2 on H1/H2,
>     # but on veth0 on H2
>     ip link set down dev veth1 # down veth0
>     ip route show
>     [ $uts != H3 ] || ip -o route get 198.51.100.1 | grep -Fw veth0
>     [ $uts != H3 ] || ip -o route get 2001:db8:3::1 | grep -Fw veth0
>     [ $uts = H3 ] || ip -o route get 198.51.100.1 | grep -Fw veth2
>     [ $uts = H3 ] || ip -o route get 2001:db8:3::1 | grep -Fw veth2
> 
> Without this patch, the two last lines would fail on H1 (the one using
> the "all" sysctl). With the patch, everything succeeds as expected.
> 
> Also document the sysctl in `ip-sysctl.rst`.
> 
> Fixes: 0eeb075fad73 ("net: ipv4 sysctl option to ignore routes when nexthop link is down")
> Signed-off-by: Vincent Bernat <vincent@...nat.ch>
> ---
>  Documentation/networking/ip-sysctl.rst | 3 +++
>  include/linux/inetdevice.h             | 2 +-
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
> index 837d51f9e1fa..fb6e4658fd4f 100644
> --- a/Documentation/networking/ip-sysctl.rst
> +++ b/Documentation/networking/ip-sysctl.rst
> @@ -1552,6 +1552,9 @@ igmpv3_unsolicited_report_interval - INTEGER
>  
>  	Default: 1000 (1 seconds)
>  
> +ignore_routes_with_linkdown - BOOLEAN
> +        Ignore routes whose link is down when performing a FIB lookup.
> +
>  promote_secondaries - BOOLEAN
>  	When a primary IP address is removed from this interface
>  	promote a corresponding secondary IP address instead of
> diff --git a/include/linux/inetdevice.h b/include/linux/inetdevice.h
> index 3515ca64e638..3bbcddd22df8 100644
> --- a/include/linux/inetdevice.h
> +++ b/include/linux/inetdevice.h
> @@ -126,7 +126,7 @@ static inline void ipv4_devconf_setall(struct in_device *in_dev)
>  	  IN_DEV_ORCONF((in_dev), ACCEPT_REDIRECTS)))
>  
>  #define IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev) \
> -	IN_DEV_CONF_GET((in_dev), IGNORE_ROUTES_WITH_LINKDOWN)
> +	IN_DEV_ORCONF((in_dev), IGNORE_ROUTES_WITH_LINKDOWN)
>  
>  #define IN_DEV_ARPFILTER(in_dev)	IN_DEV_ORCONF((in_dev), ARPFILTER)
>  #define IN_DEV_ARP_ACCEPT(in_dev)	IN_DEV_ORCONF((in_dev), ARP_ACCEPT)
> 

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