Re: wpa_supplicant before dhcpcd

["Steven M. Bellovin" <smb%cs.columbia.edu@localhost>]

On Tue, 02 Sep 2008 17:37:47 +0100
Roy Marples <roy%marples.name@localhost> wrote:

> On Sat, 2008-08-23 at 09:39 +1000, Daniel Carosone wrote:
> > Why can you have only one instance?  Because dhclient has a control
> > socket, and multiple instances started using the same default socket
> > collide. 
> > 
> > Why does dhclient have a control socket?  So that the running
> > instance can have changes made to it, like adding and removing
> > interfaces, releasing and restarting leases, etc.
> 
> I can't see anything in the omshell manpage about adding/removing
> interfaces from a running dhclient. Are you sure this can be done?
> IIRC, the real reason only one client can be run is because they all
> want to bind a UDP port to INADDR_ANY which BSD only allows one
> instance of due to the lack of the SO_BINDTODEVICE ioctl.
> 
It speaks of creating and destroying objects, but I have no idea if
interfaces are among the objects one can deal with that way.  But note
this text from dhclient(8):


        The DHCP client normally exits if it isn't able to identify
        any network interfaces to configure.   On laptop computers
        and other computers with hot-swappable I/O buses, it is
        possible that a broadcast interface  may be  added  after
        system startup.   The -w flag can be used to cause the
        client not to exit when it doesn't  find  any  such
        interfaces.    The omshell  (1)  program can then be used
        to notify the client when a net- work interface has been
        added  or  removed,  so that  the  client  can attempt to
        configure an IP address on that interface.


                --Steve Bellovin, http://www.cs.columbia.edu/~smb