--with-ipv4-default and sshd IPv4/6 dual bind hack

Pekka Savola pekkas at netcore.fi
Tue Mar 6 07:15:04 EST 2001

On Mon, 5 Mar 2001, Damien Miller wrote:

> On Mon, 5 Mar 2001, Pekka Savola wrote:
> > Hello all,
> >
> > I just found a bug a nice bug that can be turned into a real feature on
> > systems (usually Linux) that are built with --with-ipv4-default.
> >
> > If you enable IPv6 in kernel, and enable both listenaddress and
> > ::, sshd will error out 'address family not supported'.
> >
> > However, you can work around this error by starting sshd with 'sshd -4 -6'.
> >
> > As far as man page is concerned, I'm getting the impression that you
> > should be able to use only  -4 or -6, not both.
> It may be that the reason for the hack has been fixed. Can someone
> with a recent Linux kernel with IPv6 compiled in (or module loaded)
> build OpenSSH without the --with-ipv4-default hack and see whether
> it still waits ages for nameserver lookups at connect?

Is there some design reason why sshd couldn't bind to both address
families if specified to do so (non-default behaviour) even without

Most people will probably want to use IPv4 by default.  But some would
enable IPv6 in packages as far as possible in case it doesn't hurt anyone
not using it.

Pekka Savola                  "Tell me of difficulties surmounted,
Netcore Oy                    not those you stumble over and fall"
Systems. Networks. Security.   -- Robert Jordan: A Crown of Swords

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