this is a quickie expect script to check for changed dns/ip number.

just change the source and target ip's in 'changed' and the 'same'
procedures, and in the 'expect {}' block.

set logname "r:/dns.log"
set begin [clock seconds]
set start [clock format [clock seconds] -format "%c"]
set logid "--"
set newsession 1
set this_long 3600

proc quit {} {
     uptime
     exit
}
proc uptime {} {
     global begin start newsession 
     set uptime [duration 0]

     set end [clock seconds]
     set elapsed [expr $end-$begin]
     set thisrun $elapsed
     set trund [expr ($thisrun / 3600) / 24]
     set trunh [expr ($thisrun / 3600) % 24]
     if {$trunh<1} {
         set trunh "0"
     }
      if {$trunh>=1 && $trunh<10} {
           set trunh "0$trunh"
     }
     set trunm [expr ($thisrun % 3600) / 60]
      if {$trunm<1} {
           set trunm "0"
    }
    logmsg "---------------------------------------------------"
    logmsg "dnstest  running for:  $trund\d $trunh\h $trunm\m"
    logmsg "---------------------------------------------------"
}
proc duration { int_time } {
     global timetowait up
     lappend timeList ""
     if {[set d [expr ($int_time / 3600) / 24]] > 1} {
        lappend timeList "$d\d"
	} else {
	   if {$d<1} {
	      lappend timeList "0d"
	   }
	}
	
	if {[set h [expr ($int_time / 3600) % 24]] > 1} {
	   lappend timeList "$h\h"
	} else {
	  if {$h<1} {
	   lappend timeList "0h"
 	  }
	}
	if {[set m [expr ($int_time % 3600) / 60]] > 1} {
	   if {$m<5 && $up==0} {set timetowait 1}
	   if {$m>5 && $up} {set timetowait 5}
        lappend timeList "$m\m"
     } else {
	  if {$m<1} {
	     lappend timeList "0m"
	  }
	}
	if {[set s [expr ($int_time % 3600) % 60]] > 1} {
	   lappend timeList "$s\s"
	} else {
	  if {$s<=1} {
	     lappend timeList "0s"
	  }
	}
	return [join $timeList]
}
proc logwindow {} {
     wm geometry . +265+285
     wm title . "dns messages"
     wm resizable . 0 0
     wm minsize . 425 100

     frame .logwindow
     text .logwindow.buffer  -yscrollcommand  ".logwindow.sb set"
-width 85 -height 15 -wrap word -bg black -fg green -takefocus 1
     scrollbar .logwindow.sb -command ".logwindow.buffer yview"
     frame .bf
     button .bf.exit -text "Exit" -command {quit}
     button .bf.uptime -text "Uptime" -command {uptime}
     pack .bf -side bottom
     pack .bf.uptime -side left -ipadx 114
     pack .bf.exit -side right -ipadx 114
     pack .logwindow
     pack .logwindow.sb -side right -fill y
     pack .logwindow.buffer -side left
     raise .
}
proc logmsg {msg} {
     global logname logid newsession

     set  timestamp [clock format [clock seconds] -format "%d %b %H:%M:%S"]
     set  logfile [open $logname a+]

     if {$newsession==1} {
         puts $logfile "\n  $timestamp  $logid $msg"
         .logwindow.buffer insert end "\n  $timestamp  $logid $msg\n"
         .logwindow.buffer see end; update idle
     }  else {
         puts $logfile "  $timestamp  $logid $msg"
         .logwindow.buffer insert end "  $timestamp  $logid $msg\n"
         .logwindow.buffer  see end; update idle
     }
     close $logfile
     set newsession 0
}
proc changed  {} {
     logmsg "dns changed to: 192.168.100.2"
     exit 
}
proc same  {} {
     logmsg "dns the same at: 192.168.100.1"
}
proc testnode {} {
     global this_long 
     while {1} {
          spawn ping iblog.us
          set timeout 15
          expect {
            {192.168.100.2}   {changed }
            {192.168.100.1}   {same }
                default     {same}
          }
          sleep $this_long
     }
}
trap {
     set sig [trap -name]
     uptime
     logmsg "--------------------"
     logmsg "Exiting via SIG$sig"
     logmsg "--------------------"
     quit
} {SIGINT SIGTERM SIGQUIT}

logwindow
logmsg "---------------------------------------------------"
logmsg "started testing on: $start"
logmsg "---------------------------------------------------"
testnode
uptime

--- PPoint 3.05 b2