netdev - netstat and dual stack sockets

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Message-ID: <20150615205421.GA22616@orbit.nwl.cc>
Date:	Mon, 15 Jun 2015 22:54:21 +0200
From:	Phil Sutter <phil@....cc>
To:	netdev@...r.kernel.org
Subject: netstat and dual stack sockets

Hi,

A socket listening on any AF_INET6 address will receive IPv4 traffic as
well, as long as it does not set IPV6_V6ONLY (or sysctl
net.ipv6.bindv6only is set). Apache APR e.g. explicitly disables
IPV6_V6ONLY for listening sockets.

As I see it, a user has no way of detecting the listening socket in this
address family: it does not show in /proc/net/{tcp,udp} nor do
'netstat', 'ss' or 'lsof' print any additional information about those
sockets over pure IPv6 ones.

Is this correct? If so, are there any intentions to export the missing
information to userspace?

Phil
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