netdev - Re: [PATCH net-next] net: dsa: Allow port mirroring to the CPU port

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Message-Id: <20191003.120457.1626857609490915856.davem@davemloft.net>
Date:   Thu, 03 Oct 2019 12:04:57 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     olteanv@...il.com
Cc:     andrew@...n.ch, f.fainelli@...il.com, vivien.didelot@...il.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: dsa: Allow port mirroring to the CPU port

From: Vladimir Oltean <olteanv@...il.com>
Date: Thu,  3 Oct 2019 02:37:50 +0300

> On a regular netdev, putting it in promiscuous mode means receiving all
> traffic passing through it, whether or not it was destined to its MAC
> address. Then monitoring applications such as tcpdump can see all
> traffic transiting it.
> 
> On Ethernet switches, clearly all ports are in promiscuous mode by
> definition, since they accept frames destined to any MAC address.
> However tcpdump does not capture all frames transiting switch ports,
> only the ones destined to, or originating from the CPU port.
> 
> To be able to monitor frames with tcpdump on the CPU port, extend the tc
> matchall classifier and mirred action to support the DSA master port as
> a possible mirror target.
> 
> Tested with:
> tc qdisc add dev swp2 clsact
> tc filter add dev swp2 ingress matchall skip_sw \
> 	action mirred egress mirror dev eth2
> tcpdump -i swp2
> 
> Signed-off-by: Vladimir Oltean <olteanv@...il.com>

Andrew and co., please review.