netdev - Re: [PATCH 1/4] net: arp: introduce arp_evict

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Message-ID: <1d503584-e463-3324-140a-14c86521cd59@gmail.com>
Date:   Thu, 14 Oct 2021 12:34:27 -0600
From:   David Ahern <dsahern@...il.com>
To:     James Prestwood <prestwoj@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/4] net: arp: introduce arp_evict_nocarrier sysctl
 parameter

On 10/13/21 4:27 PM, James Prestwood wrote:
> This change introduces a new sysctl parameter, arp_evict_nocarrier.
> When set (default) the ARP cache will be cleared on a NOCARRIER event.
> This new option has been defaulted to '1' which maintains existing
> behavior.
> 
> Clearing the ARP cache on NOCARRIER is relatively new, introduced by:
> 
> commit 859bd2ef1fc1110a8031b967ee656c53a6260a76
> Author: David Ahern <dsahern@...il.com>
> Date:   Thu Oct 11 20:33:49 2018 -0700
> 
>     net: Evict neighbor entries on carrier down
> 
> The reason for this changes is to prevent the ARP cache from being
> cleared when a wireless device roams. Specifically for wireless roams
> the ARP cache should not be cleared because the underlying network has not
> changed. Clearing the ARP cache in this case can introduce significant
> delays sending out packets after a roam.

how do you know if the existing ARP / ND entries are valid when roaming?