netdev - Re: [PATCH net-next 2/3] net: ipv4: flush neighbor entries when carrier is off

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Message-ID: <20171106104725.GA2765@shredder.mtl.com>
Date:   Mon, 6 Nov 2017 12:47:25 +0200
From:   Ido Schimmel <idosch@...sch.org>
To:     David Ahern <dsahern@...il.com>
Cc:     netdev@...r.kernel.org, jhs@...atatu.com,
        Satish Ashok <sashok@...ulusnetworks.com>
Subject: Re: [PATCH net-next 2/3] net: ipv4: flush neighbor entries when
 carrier is off

Hi David,

On Sun, Nov 05, 2017 at 10:57:52PM -0800, David Ahern wrote:
> Commit a6db4494d218c ("net: ipv4: Consider failed nexthops in multipath
> routes") added support for checking neighbor state when selecting a path
> for multipath route lookups. It works but incurs a delay waiting for
> the neighbor entry to timeout. Improve the path selection by flushing
> non-permanent neighbor entries when carrier is off.
> 
> Signed-off-by: Satish Ashok <sashok@...ulusnetworks.com>
> Signed-off-by: David Ahern <dsahern@...il.com>
> ---
>  net/ipv4/fib_frontend.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
> index f02819134ba2..aa8fea74858f 100644
> --- a/net/ipv4/fib_frontend.c
> +++ b/net/ipv4/fib_frontend.c
> @@ -1226,10 +1226,13 @@ static int fib_netdev_event(struct notifier_block *this, unsigned long event, vo
>  		break;
>  	case NETDEV_CHANGE:
>  		flags = dev_get_flags(dev);
> -		if (flags & (IFF_RUNNING | IFF_LOWER_UP))
> +		if (flags & (IFF_RUNNING | IFF_LOWER_UP)) {
>  			fib_sync_up(dev, RTNH_F_LINKDOWN);
> -		else
> +		} else {
>  			fib_sync_down_dev(dev, event, false);
> +			if (IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev))

Can you please explain why the flushing is conditioned on this sysctl
being enabled? If carrier is down and the sysctl is enabled, then the
nexthop will not be used anyway.

Thanks

> +				neigh_carrier_down(&arp_tbl, dev);
> +		}
>  		/* fall through */
>  	case NETDEV_CHANGEMTU:
>  		rt_cache_flush(net);
> -- 
> 2.1.4
>