On Fri, Nov 22, 2002 at 10:57:18AM -0500, Steve Bellovin wrote:
  | I want to ensure that dhclient only runs on certain interfaces, to 
  | prevent it from overwriting the static address for vmnet1.  I can't set 
  | dhclient_flags, because wi0 is sometimes present and sometimes not.  
  | Instead, I wrote the following script, which I put into
  | /etc/rc.conf.d/dhclient (though it could -- should? -- go into
  | /etc/rc.d/dhclient.

There's an easier way; just list the interfaces you want dhclient to
attempt to use in /etc/dhclient.conf.  For example, on my laptop I have:

	interface "wi0" {
		media "-mediaopt adhoc nwid SOMETHING nwkey SOMETHINGELSE";
		media "-mediaopt adhoc nwid '' -nwkey";
		media "mediaopt adhoc -nwkey";
	}

	interface "tlp0" {
	}

dhclient only tries wi0 (if present), cycling through the media
options on each retry, and tlp0 (if present); it doesn't try other 
"broadcast capable" interfaces that may be available.

I'd be curious to know if this solution works for you or not.

Luke.



  | 
  | 
  | 
  | #!/bin/sh
  | 
  | dhclient_precmd()
  | {
  |         if [ "x$dhclient_flags" = x -a -f /etc/dhcpinterface ]
  |         then
  |                 iface="/"
  |                 for i in `ifconfig -l`
  |                 do
  |                         iface="$iface$i/"
  |                 done
  | 
  |                 rc_flags=""
  |                 while read x
  |                 do
  |                         if expr "$x" : "#" >/dev/null
  |                         then
  |                                 continue
  |                         fi
  |                         if expr "$iface" : ".*/$x/" >/dev/null
  |                         then
  |                                 rc_flags="$rc_flags $x"
  |                         fi
  |                 done </etc/dhcpinterface
  |                 echo $rc_flags
  |         fi
  | }
  | 
  | start_precmd=dhclient_precmd
  | restart_precmd=dhclient_precmd
  | 
  | 
  | The file /etc/dhcpinterface lists the allowable dhcp interfaces; 
  | however, only those that actually exist are passed in.  There are some 
  | obvious and easy ways to accomplish the match more easily; however, I 
  | needed something that only used commands in /bin, because at boot time 
  | dhclient runs before /usr is mounted.  (Let's not dredge up *that* 
  | argument again....)
  | 
  | The script is skipped if dhclient_flags has been set explicitly by the 
  | user.  (Should I be checking rc_flags there?)
  | 
  | In my /etc/apm/resume script, I invoked '/etc/rc.d/dhclient restart'.
  | 
  | 
  | 		--Steve Bellovin, http://www.research.att.com/~smb (me)
  | 		http://www.wilyhacker.com ("Firewalls" book)
  |