Your Own Domain Name with External DHCP for Slackware on a Gateway

This article assumes the reader is familiar with the contents of owndomain.html.

In this scenario we are running Slackware Linux on an Internet gateway, obtaining its dynamic external IP address using DHCP.

Ideally, choose dynamic DNS services that do not themselves have dynamic IP addresses, and whose name server names are inside there own domains. This will give more efficiency, and some resolver programs will choke on two many levels of indirection, despite what the RFC-s say.

The zone file would contain something like:

$TTL 1D
you.ca.     SOA   you.ca. root.you.ca. (
                    20020101      ;serial
                    3600          ;refresh
                    1800          ;retry
                    604800        ;expiration
                    0             ;TTL for NACK
                    )
you.ca.     NS    you.dyndnservice1.ca.
you.ca.     NS    you.dyndnservice2.ca.
$ORIGIN you.ca.
$INCLUDE /etc/bind/IP-address

Make sure that the gateway will boot (to the point where there is a login prompt on the gateway console) with the DSL or cable modem unplugged! This means named has to be restarted again right after booting, but makes things much simpler and grief free.

Start a script that uses ISC dhlient in background using "&" after everything is up using /etc/rc.d/rc.local:

#!/bin/sh
#
# /etc/rc.d/rc.local:  Local system initialization script.
#
# Put any local setup commands in here:

# set up external interface
echo "Attempting to configure eth1 by contacting a DHCP server..."
/bin/touch /var/log/dhclient-at-boot
/usr/local/dhcp/sbin/dhclient eth1 &> /dev/null 2>&1 &

echo Starting fetchmail daemon ...
/etc/rc.d/rc.fetchmail 2>&1 | /usr/bin/logger -t rc.fetchmail -s &

Provide an "enter hooks" script for dhclient - /etc/dhclient-enter-hooks:

#!/bin/sh

# enter hooks for dhclient-script

# do not overwrite /etc/resolv.conf
function make_resolv_conf() { return; }

Provide an "exit hooks" script for dhclient - /etc/dhclient-exit-hooks:

#!/bin/sh

# exit hooks for dhclient-script

# for debugging
#( \
#  echo ==== start of debug dump ==== ; \
#  echo parms: $* ; \
#  env ; \
#  echo ====  end of debug dump  ==== ; \
#  ) | /usr/bin/logger -t rc.dhclient-exit-hooks

# call our setup script if dhclient has set up interface
if [ x$reason = xBOUND   ] || [ x$reason = xRENEW  ] || \
   [ x$reason = xREBIND  ] || [ x$reason = xREBOOT ] || \
   [ x$reason = xTIMEOUT ]; then
  /etc/rc.d/rc.dhclient_exit 2>&1 | /usr/bin/logger -t rc.dhclient_exit &
  exit
fi

# set up interface ourselves and call our setup script
if [ x$reason = xEXPIRE  ] || [ x$reason = xFAIL ] || \
   [ x$reason = xRELEASE ] || [ x$reason = xSTOP ]; then
  if [ x$old_ip_address = x ]; then
    if [ -r /var/log/dhclient-addresses ]; then
      read zzz old_ip_address < /var/log/dhclient-addresses
    fi
  fi
  if [ x$old_ip_address = x ]; then
    # provide a last ditch default? comment out exit
    old_ip_address=10.10.10.10
    exit
  fi
  ifconfig $interface inet $old_ip_address
  export new_ip_address=$old_ip_address
  /etc/rc.d/rc.dhclient_exit 2>&1 | /usr/bin/logger -t rc.dhclient_exit &
  exit
fi

You may also want to replace the call to the "ping" command in the "TIMEOUT" section of the "sbin/dhclient-script" script (part of ISC DHCP) with a call to the "true" command. Without this, if your ISP's router is down, the "ping" command may run indefinitely.

The "exit hooks" script for dhclient calls /etc/rc.d/rc.dhclient_exit:

#!/bin/sh

# read old IP address
if [ -r /var/log/dhclient-addresses ]
then
  read zzz old_ip_address < /var/log/dhclient-addresses
fi
if [ "$old_ip_address" == "" ]
then
  old_ip_address="0.0.0.0"
fi

# (re)erect firewall if address changed or boot time
if [ "$old_ip_address" != "$new_ip_address" ] ||
   [ -e /var/log/dhclient-at-boot ]
then
  # ensure kernel had time to set up interface
  #/usr/bin/sleep 1
  # reset firewall
  /bin/echo \(re\)setting firewall ...
  /etc/rc.d/rc.firewall
fi

# record old and new IP addresses
/bin/echo -n $old_ip_address $new_ip_address &> /var/log/dhclient-addresses

# say whether or not IP address changed
if [ "$old_ip_address" == "$new_ip_address" ]
then
  /bin/echo IP address has not changed
else
  /bin/echo IP address has changed from $old_ip_address to $new_ip_address
fi

# configure BIND
/bin/echo mail     IN  CNAME mail.$new_domain_name. >  /etc/bind/services
/bin/echo news     IN  CNAME news.$new_domain_name. >> /etc/bind/services
/bin/echo www      IN  CNAME www.$new_domain_name.  >> /etc/bind/services
#
/bin/echo "@  IN A" $new_ip_address > /etc/bind/IP-address
#
/bin/echo zone \"$new_domain_name\" { type forward\; forwarders { > /etc/bind/forward
for nameserver in $new_domain_name_servers
do
  /bin/echo $nameserver\; >> /etc/bind/forward
done
/bin/echo }\; }\; >>  /etc/bind/forward
#
/bin/echo BIND has been configured
# IP address changed?
if [ "$old_ip_address" != "$new_ip_address" ]
then

  # update address in local dynamic zones
  /bin/echo Updating addresses for dynamic zones to $new_ip_address
  /usr/local/bind/bin/nsupdate -v -k \
    /usr/local/gnudip/etc/Kgnudip-key.+157+41184.private << EOF
server localhost
update delete dyn.you.ca.    A
update add    dyn.you.ca. 60 A $new_ip_address

update delete dyn2.you.ca.    A
update add    dyn2.you.ca. 60 A $new_ip_address

EOF
  /bin/echo
  /usr/local/bind/bin/host dyn.you.ca.
  /usr/local/bind/bin/host dyn2.you.ca.

fi

# restart affected daemons if address changed or boot time
if [ "$old_ip_address" != "$new_ip_address" ] ||
   [ -e /var/log/dhclient-at-boot ]
then

  # restart named
  if /bin/ps -C named &> /dev/null
  then
    /bin/echo Stopping named ...
    /bin/killall named
  fi
  /bin/echo Starting named ...
  /etc/rc.d/rc.named

  # (re)start ntpd
  if /bin/ps -C ntpd &> /dev/null
  then
    /bin/echo Stopping ntpd ...
    /bin/killall ntpd
  else
    /bin/echo Calling ntpdate ...
    /usr/local/ntp/bin/ntpdate ddd.ddd.ddd.ddd
  fi
  /bin/echo Starting ntpd ...
  /usr/local/ntp/bin/ntpd

  # (re)start iplog
  if /bin/ps -C iplog &> /dev/null
  then
    /bin/echo Stopping iplog ...
    /bin/killall iplog
  fi
  /bin/echo Starting iplog ...
  /usr/local/iplog/sbin/iplog

fi

# no longer boot time
/bin/rm /var/log/dhclient-at-boot &> /dev/null

# update dynamic DNS services?
/etc/rc.d/rc.dyndns

And /etc/rc.d/rc.dhclient_exit calls /etc/rc.d/rc.dyndns:

#!/bin/sh
#
# rc.dyndns
#
# update dynamic DNS services if needed

echo Updating IP address at GnuDIP servers ...
/usr/local/gdipc/bin/gdipc.pl -f /etc/gdipc/gdipc.conf

echo Updating IP address at notgnudip.org ...
/usr/local/ez-ipupdate/bin/notgnudip.org.conf

Some daemons have to be restarted when the address changes, because they are listening on specific IP addresses, and will not automatically listen on the new address (use "netstat -ap | less -S" to see which). This applies to named. Also you may want to supply named with information from DHCP which has to go in named.conf. So named has to be restarted. You could make the zones for your internal machines and you.ca dynamic, but you may find it more convenient to be able to edit the files (and use $INCLUDE).