netdev - Re: [PATCH net-next] vxlan: remove fdb when out interface is removed

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Message-Id: <20200529.164227.1281408645512421293.davem@davemloft.net>
Date:   Fri, 29 May 2020 16:42:27 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     ap420073@...il.com
Cc:     kuba@...nel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] vxlan: remove fdb when out interface is
 removed

From: Taehee Yoo <ap420073@...il.com>
Date: Wed, 27 May 2020 16:29:50 +0000

> vxlan fdb can have NDA_IFINDEX, which indicates an out interface.
> If the interface is removed, that fdb will not work.
> So, when interface is removed, vxlan's fdb can be removed.
> 
> Test commands:
>     ip link add dummy0 type dummy
>     ip link add vxlan0 type vxlan vni 1000
>     bridge fdb add 11:22:33:44:55:66 dst 1.1.1.1 dev vxlan0 via dummy0 self
>     ip link del dummy0
> 
> Before this patch, fdbs will not be removed.
> Result:
>     bridge fdb show dev vxlan0
> 11:22:33:44:55:66 dst 1.1.1.1 via if10 self permanent
> 
> 'if10' indicates 'dummy0' interface index.
> But the dummy0 interface was removed so this fdb will not work.
> 
> Signed-off-by: Taehee Yoo <ap420073@...il.com>

But if someone adds an interface afterwards with ifindex 10 that FDB
entry will start using it.

I don't know how desirable that is, but if someone is depending upon
that behavior now this change will break things for them.