Re: netstat and dual stack sockets

[Phil Sutter <phil@nwl.cc>]

HGN!

On Mon, Jun 15, 2015 at 11:36:54PM +0200, Hagen Paul Pfeifer wrote:
> On 15 June 2015 at 22:54, Phil Sutter <phil@nwl.cc> wrote:
> 
> > 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.
> 
> Probably a combination of IPV6_V6ONLY(1, 0) and IN6_IS_ADDR_V4MAPPED
> fulfills all user requirements, ... so far. Your proposal is to hand
> over sk->sk_ipv6only?

Not sure if I understand you correctly - of course it is possible to
programmatically determine whether a socket one has opened accepts
v4mapped addresses or a given address is v4mapped. My concern is about
the system administrator's point of view, using system tools to find out
on which IP addresses and ports a machine is accessible. Looking at e.g.
/proc/net/tcp6 does not reveal if a listening socket also accepts
v4mapped addresses, factually acting as AF_INET socket upon request.

Cheers, Phil