netdev - Re: [PATCH net-next] ipv4/fib: send RTM

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Message-ID: <20230718085814.4301b9dd@hermes.local>
Date: Tue, 18 Jul 2023 08:58:14 -0700
From: Stephen Hemminger <stephen@...workplumber.org>
To: Ido Schimmel <idosch@...sch.org>
Cc: Hangbin Liu <liuhangbin@...il.com>, netdev@...r.kernel.org, "David S .
 Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>, Thomas Haller <thaller@...hat.com>
Subject: Re: [PATCH net-next] ipv4/fib: send RTM_DELROUTE notify when flush
 fib

On Tue, 18 Jul 2023 13:19:06 +0300
Ido Schimmel <idosch@...sch.org> wrote:

> fib_table_flush() isn't only called when an address is deleted, but also
> when an interface is deleted or put down. The lack of notification in
> these cases is deliberate. Commit 7c6bb7d2faaf ("net/ipv6: Add knob to
> skip DELROUTE message on device down") introduced a sysctl to make IPv6
> behave like IPv4 in this regard, but this patch breaks it.
> 
> IMO, the number of routes being flushed because a preferred source
> address is deleted is significantly lower compared to interface down /
> deletion, so generating notifications in this case is probably OK. It
> also seems to be consistent with IPv6 given that rt6_remove_prefsrc()
> calls fib6_clean_all() and not fib6_clean_all_skip_notify().

Agree. Imagine the case of 3 million routes and device goes down.
There is a reason IPv4 behaves the way it does.