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List:       dhcp-client
Subject:    FreeBSD (and perhaps other) dhclient-script bugs
From:       "Michael C. Adler" <madler () vssad ! hlo ! dec ! com>
Date:       1999-12-07 4:49:01
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At least on FreeBSD I've encountered some dhclient-script bugs.  I'm
using V2.0 but the script for the current version is basically the same
and still has bugs.

The basic problem is that there are a number of cases in which dhclient
may invoke dhclient-script with $old_ip_address empty in spite of the
fact that the script has already been invoked and the interface is
actually configured.  I can get both BOUND and REBOOT to be called in
different circumstances.  I believe BOUND is called when the DHCP server
changes and offers a different IP address.  I believe REBOOT is called
if dhclient is killed and restarted.  In neither case was
$old_ip_address set for me.

In any event, it is relatively simple to change dhclient-script to
handle this case as long as no aliases have been declared and the
routing table only has a default root.  For those cases, I now delete
the default root and clear the arp table whenever ifconfig is invoked to
set up an IP address.

There is also a race condition in the existing dhclient-script.  For
BOUND, REBOUND, etc., the arp table is cleared when old_ip_address
exists BEFORE ifconfig is invoked to rebind the interface.  There is a
short window between the two in which the arp table could be repopulated
with soon to be invalid entries.

I've also found the route add $new_ip_address 127.1 lines to cause
nothing but trouble for me on FreeBSD 3.3 and commented them out.  Are
they necessary?

Am I misunderstanding something?  I've attached my patch file for V2.0.

-Michael

-- Attached file included as plaintext by Listar --
-- File: freebsd.patch

*** freebsd.orig	Mon Dec  6 23:29:44 1999
--- freebsd	Mon Dec  6 23:29:41 1999
***************
*** 61,68 ****
--- 61,72 ----
      ifconfig $interface inet -alias $alias_ip_address > /dev/null 2>&1
      route delete $alias_ip_address 127.0.0.1 > /dev/null 2>&1
    fi
+   if [ `netstat -nr | grep -c default` -gt 0 ]; then
+     route delete default
+   fi
    ifconfig $interface inet 0.0.0.0 netmask 0.0.0.0 \
  		broadcast 255.255.255.255 up
+   arp -n -a | sed -n -e 's/^.*(\(.*\)) at .*$/arp -n -d \1/p' |sh
    exit_with_hooks 0
  fi
  
***************
*** 90,102 ****
  	shift; shift
        done
      fi
-     arp -n -a | sed -n -e 's/^.*(\(.*\)) at .*$/arp -n -d \1/p' |sh
    fi
    if [ x$old_ip_address = x ] || [ x$old_ip_address != x$new_ip_address ] || \
       [ x$reason = xBOUND ] || [ x$reason = xREBOOT ]; then
      ifconfig $interface inet $new_ip_address $new_netmask_arg \
  					$new_broadcast_arg $medium
!     route add $new_ip_address 127.1 >/dev/null 2>&1
      for router in $new_routers; do
        route add default $router >/dev/null 2>&1
      done
--- 94,108 ----
  	shift; shift
        done
      fi
    fi
    if [ x$old_ip_address = x ] || [ x$old_ip_address != x$new_ip_address ] || \
       [ x$reason = xBOUND ] || [ x$reason = xREBOOT ]; then
+     if [ `netstat -nr | grep -c default` -gt 0 ]; then
+       route delete default
+     fi
      ifconfig $interface inet $new_ip_address $new_netmask_arg \
  					$new_broadcast_arg $medium
! #    route add $new_ip_address 127.1 >/dev/null 2>&1
      for router in $new_routers; do
        route add default $router >/dev/null 2>&1
      done
***************
*** 107,112 ****
--- 113,119 ----
  	shift; shift
        done
      fi
+     arp -n -a | sed -n -e 's/^.*(\(.*\)) at .*$/arp -n -d \1/p' |sh
    fi
    if [ x$new_ip_address != x$alias_ip_address ] && [ x$alias_ip_address != x ];
     then
***************
*** 164,170 ****
  	ifconfig $interface inet alias $alias_ip_address $alias_subnet_arg
  	route add $alias_ip_address 127.0.0.1
        fi
!       route add $new_ip_address 127.1 >/dev/null 2>&1
        for router in $new_routers; do
  	route add default $router >/dev/null 2>&1
        done
--- 171,177 ----
  	ifconfig $interface inet alias $alias_ip_address $alias_subnet_arg
  	route add $alias_ip_address 127.0.0.1
        fi
! #      route add $new_ip_address 127.1 >/dev/null 2>&1
        for router in $new_routers; do
  	route add default $router >/dev/null 2>&1
        done


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