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Date:   Thu, 27 Aug 2020 19:40:15 +0200
From:   Florian Westphal <fw@strlen.de>
To:     Phil Sutter <phil@nwl.cc>,
        Quentin Armitage <quentin@armitage.org.uk>,
        netfilter-devel@vger.kernel.org, Florian Westphal <fw@strlen.de>
Subject: Re: [PATCH] netfilter: nftables: fix documentation for dup statement
Message-ID: <20200827174015.GC7319@breakpoint.cc>
References: <f9bc9e191b03728fe233ca7a75fdc40ede0fde8e.camel@armitage.org.uk>
 <20200827170203.GM23632@orbyte.nwl.cc>
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Phil Sutter <phil@nwl.cc> wrote:
> Hi,
> 
> On Thu, Aug 27, 2020 at 04:42:00PM +0100, Quentin Armitage wrote:
> > The dup statement requires an address, and the device is optional,
> > not the other way round.
> > 
> > Signed-off-by: Quentin Armitage <quentin@armitage.org.uk>
> > ---
> >  doc/statements.txt | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/doc/statements.txt b/doc/statements.txt
> > index 9155f286..835db087 100644
> > --- a/doc/statements.txt
> > +++ b/doc/statements.txt
> > @@ -648,7 +648,7 @@ The dup statement is used to duplicate a packet and send the
> > copy to a different
> >  destination.
> >  
> >  [verse]
> > -*dup to* 'device'
> > +*dup to* 'address'
> >  *dup to* 'address' *device* 'device'
> >  
> >  .Dup statement values
> 
> The examples are wrong, too. I wonder if this is really just a mistake
> and all three examples given (including the "advanced" usage using a
> map) are just wrong or if 'dup' actually was meant to support
> duplicating to a device in mirror port fashion.

Right, 'dup to eth0' can be used in the netdev ingress hook.

For dup from ipv4/ipv6 families the address is needed.