From mboxrd@z Thu Jan  1 00:00:00 1970
From: Phil Sutter <phil@nwl.cc>
Subject: Re: [PATCH iproute2] ip-address: properly display zero IPv4 peer
 address
Date: Wed, 11 Nov 2015 12:34:02 +0100
Message-ID: <20151111113402.GQ26876@orbit.nwl.cc>
References: <1445502868-29474-1-git-send-email-thaller@redhat.com>
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Cc: netdev@vger.kernel.org,
	Stephen Hemminger <stephen@networkplumber.org>
To: Thomas Haller <thaller@redhat.com>
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On Thu, Oct 22, 2015 at 10:34:28AM +0200, Thomas Haller wrote:
> Kernel allows for zero IPv4 peer addresses (IFA_ADDRESS):
> 
>    ip address add 192.168.5.1 peer 0.0.0.0/24 dev dummy
> 
> which is distinct from a usual address like:
> 
>    ip address add 192.168.5.1/24 dev dummy
>    ip address add 192.168.5.1 peer 192.168.5.1/24 dev dummy
> 
> For IPv4, a missing IFA_ADDRESS attribute means that the peer
> is 0.0.0.0. See inet_fill_ifaddr(), which does:
> 
>   if ((ifa->ifa_address &&
>        nla_put_in_addr(skb, IFA_ADDRESS, ifa->ifa_address)) ||
> 
> Signed-off-by: Thomas Haller <thaller@redhat.com>

Acked-by: Phil Sutter <phil@nwl.cc>

I wonder why this is not the case for IPv6. What is the functional
effect of setting a zero peer with non-zero netmask?

Cheers, Phil