netdev - Re: [PATCH 2/3] net: ndisc: introduce ndisc_evict

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Date:   Mon, 1 Nov 2021 19:37:47 -0600
From:   David Ahern <dsahern@...il.com>
To:     James Prestwood <prestwoj@...il.com>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, corbet@....net,
        yoshfuji@...ux-ipv6.org, dsahern@...nel.org, roopa@...dia.com,
        daniel@...earbox.net, vladimir.oltean@....com, idosch@...dia.com,
        nikolay@...dia.com, yajun.deng@...ux.dev, zhutong@...zon.com,
        johannes@...solutions.net, jouni@...eaurora.org
Subject: Re: [PATCH 2/3] net: ndisc: introduce ndisc_evict_nocarrier sysctl
 parameter

On 11/1/21 11:36 AM, James Prestwood wrote:
> In most situations the neighbor discovery cache should be cleared on a
> NOCARRIER event which is currently done unconditionally. But for wireless
> roams the neighbor discovery cache can and should remain intact since
> the underlying network has not changed.
> 
> This patch introduces a sysctl option ndisc_evict_nocarrier which can
> be disabled by a wireless supplicant during a roam. This allows packets
> to be sent after a roam immediately without having to wait for
> neighbor discovery.
> 
> A user reported roughly a 1 second delay after a roam before packets
> could be sent out (note, on IPv4). This delay was due to the ARP
> cache being cleared. During testing of this same scenario using IPv6
> no delay was noticed, but regardless there is no reason to clear
> the ndisc cache for wireless roams.
> 
> Signed-off-by: James Prestwood <prestwoj@...il.com>
> ---
>  Documentation/networking/ip-sysctl.rst |  9 +++++++++
>  include/linux/ipv6.h                   |  1 +
>  include/uapi/linux/ipv6.h              |  1 +
>  net/ipv6/addrconf.c                    | 12 ++++++++++++
>  net/ipv6/ndisc.c                       | 12 +++++++++++-
>  5 files changed, 34 insertions(+), 1 deletion(-)
> 

Reviewed-by: David Ahern <dsahern@...nel.org>