Configure DHCP to update DNS records: Difference between revisions

From SambaWiki
m (/* Added 'failover')
(dhcp-dyndns.sh: Read output of dns query directly into array to avoid issues with globs)
 
(35 intermediate revisions by 5 users not shown)
Line 1: Line 1:
= Introduction =
= Introduction =


This HowTo describes how to configure isc DHCP to update a Samba DC BIND DNS backend. See [[Setting_up_a_BIND_DNS_Server]] for how to set up Bind.
This HowTo describes how to configure isc DHCP to update Samba dns records in AD.


It has not been tested with the Samba 4 internal DNS server and it probably will not work with the Samba 4 internal DNS.
It has now been tested with the Samba AD internal DNS server and BIND9_DLZ.


As this HowTo is based on a Debian OS install, the paths given may be different if you use another OS.
This HowTo is based on a Debian OS install, the paths given may be different if you use another OS.

The script has now been modified to use <code>samba-tool</code> instead of <code>nsupdate</code>, it also can optionally add the <code>macAddress</code> attribute to a computers AD object, this attribute will contain the computers MAC address.




Line 11: Line 13:
= Preconditions =
= Preconditions =


* The computer has been provisioned as an AD DC and the samba, smbd and winbindd daemons are running.
* Bind9 is installed and working with the Samba 4 DC, tested with various 9.x versions


* You have created any required reverse zones.
* you are logged into the DC as 'root'

* You are logged into the DC as 'root'

* If using Bind9, Bind9_dlz must be installed and working on the Samba AD DC that you are doing this on. Tested with various 9.x versions.




Line 38: Line 44:
# apt-get install isc-dhcp-server
# apt-get install isc-dhcp-server


Or on FreeBSD:

# pkg install isc-dhcp44-server


= Create a user to carry out the updates =
= Create a user to carry out the updates =
Line 51: Line 58:
# samba-tool group addmembers DnsAdmins dhcpduser
# samba-tool group addmembers DnsAdmins dhcpduser


Now export the required keytab.
Now export the required keytab. On FreeBSD change <code>/etc/dhcpduser.keytab</code> to <code>/usr/local/etc/dhcpduser.keytab</code>

# samba-tool domain exportkeytab --principal=dhcpduser@SAMDOM.EXAMPLE.COM /etc/dhcp/dhcpduser.keytab
# chown root:root /etc/dhcp/dhcpduser.keytab
# chmod 400 /etc/dhcp/dhcpduser.keytab


# samba-tool domain exportkeytab --principal=dhcpduser@SAMDOM.EXAMPLE.COM /etc/dhcpduser.keytab
# chown root:root /etc/dhcpduser.keytab
# chmod 400 /etc/dhcpduser.keytab
{{Imbox
| type = note
| text = In the <code>chown</code> command above <code>root:root</code> is used, you need to check what user & group DHCP runs as on your distro and if different, change <code>root:root</code> to the correct user & group. On FreeBSD this is <code>dhcpd:dhcpd</code>.
}}




= Create the script for the updates =
= Create the script for the updates =


Copy this script to /usr/local/bin/dhcp-dyndns.sh
First make a directory to store the script in.

# mkdir -p /etc/dhcp/bin

Next, copy this script to /etc/dhcp/bin/dhcp-dyndns.sh


#!/bin/bash
#!/bin/bash
# On FreeBSD change the above line to #!/usr/local/bin/bash
#
# /usr/local/bin/dhcp-dyndns.sh
#
# This script is for secure DDNS updates on Samba,
# it can also add the 'macAddress' to the Computers object.
#
# Version: 0.9.6
#
# Copyright (C) Rowland Penny 2020-2022
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
# You may need to ensure that you have a useful path
# /etc/bin/dhcp-dyndns.sh
# If you have 'path' problems, Uncomment the next line and adjust for
# your setup e.g. self-compiled Samba
#export PATH=/usr/local/samba/bin:/usr/local/samba/sbin:/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin
##########################################################################
# #
# You can optionally add the 'macAddress' to the Computers object. #
# Add 'dhcpduser' to the 'Domain Admins' group if used #
# Change the next line to 'yes' to make this happen #
Add_macAddress='no'
# #
##########################################################################
# On FreeBSD change this to /usr/local/etc/dhcpduser.keytab
keytab=/etc/dhcpduser.keytab
usage()
{
cat <<-EOF
USAGE:
$(basename "$0") add ip-address dhcid|mac-address hostname
$(basename "$0") delete ip-address dhcid|mac-address
EOF
}
_KERBEROS()
{
# get current time as a number
test=$(date +%d'-'%m'-'%y' '%H':'%M':'%S)
# Note: there have been problems with this
# check that 'date' returns something like
# Check for valid kerberos ticket
#logger "${test} [dyndns] : Running check for valid kerberos ticket"
klist -c "${KRB5CCNAME}" -s
ret="$?"
if [ $ret -ne 0 ]
then
logger "${test} [dyndns] : Getting new ticket, old one has expired"
# On FreeBSD change the -F to --no-forwardable
kinit -F -k -t $keytab "${SETPRINCIPAL}"
ret="$?"
if [ $ret -ne 0 ]
then
logger "${test} [dyndns] : dhcpd kinit for dynamic DNS failed"
exit 1
fi
fi
}
rev_zone_info()
{
local RevZone="$1"
local IP="$2"
local rzoneip
rzoneip="${RevZone%.in-addr.arpa}"
local rzonenum
rzonenum=$(echo "$rzoneip" | tr '.' '\n')
declare -a words
for n in $rzonenum
do
words+=("$n")
done
local numwords="${#words[@]}"
unset ZoneIP
unset RZIP
unset IP2add
case "$numwords" in
1)
# single ip rev zone '192'
ZoneIP=$(echo "${IP}" | awk -F '.' '{print $1}')
RZIP="${rzoneip}"
IP2add=$(echo "${IP}" | awk -F '.' '{print $4"."$3"."$2}')
;;
2)
# double ip rev zone '168.192'
ZoneIP=$(echo "${IP}" | awk -F '.' '{print $1"."$2}')
RZIP=$(echo "${rzoneip}" | awk -F '.' '{print $2"."$1}')
IP2add=$(echo "${IP}" | awk -F '.' '{print $4"."$3}')
;;
3)
# triple ip rev zone '0.168.192'
ZoneIP=$(echo "${IP}" | awk -F '.' '{print $1"."$2"."$3}')
RZIP=$(echo "${rzoneip}" | awk -F '.' '{print $3"."$2"."$1}')
IP2add=$(echo "${IP}" | awk -F '.' '{print $4}')
;;
*)
# should never happen
exit 1
;;
esac
}
BINDIR=$(samba -b | grep 'BINDIR' | grep -v 'SBINDIR' | awk '{print $NF}')
<nowiki>[[ -z $BINDIR ]] && printf "Cannot find the 'samba' binary, is it installed ?\\nOr is your path set correctly ?\\n"</nowiki>
WBINFO="$BINDIR/wbinfo"
SAMBATOOL=$(command -v samba-tool)
<nowiki>[[ -z $SAMBATOOL ]] && printf "Cannot find the 'samba-tool' binary, is it installed ?\\nOr is your path set correctly ?\\n"</nowiki>
MINVER=$($SAMBATOOL -V | grep -o '[0-9]*' | tr '\n' ' ' | awk '{print $2}')
if [ "$MINVER" -gt '14' ]
then
KTYPE="--use-kerberos=required"
else
KTYPE="-k yes"
fi
# DHCP Server hostname
# This script is for secure DDNS updates on Samba 4
Server=$(hostname -s)
# Version: 0.8.7
# DNS domain
# DNS domain
domain=$(hostname -d)
domain=$(hostname -d)
if [ -z ${domain} ]; then
if [ -z "${domain}" ]
then
echo "Cannot obtain domain name, is DNS set up correctly?"
logger "Cannot obtain domain name, is DNS set up correctly?"
echo "Cannot continue... Exiting."
logger "Cannot obtain domain name, is DNS set up correctly?"
logger "Cannot continue... Exiting."
exit 1
logger "Cannot continue... Exiting."
exit 1
fi
fi
# Samba 4 realm
# Samba realm
REALM=$(echo ${domain^^})
REALM="${domain^^}"
# Additional nsupdate flags (-g already applied), e.g. "-d" for debug
#NSUPDFLAGS="-d"
# krbcc ticket cache
# krbcc ticket cache
Line 95: Line 229:
# Kerberos principal
# Kerberos principal
SETPRINCIPAL="dhcpduser@${REALM}"
SETPRINCIPAL="dhcpduser@${REALM}"
# Kerberos keytab
# Kerberos keytab as above
# krbcc ticket cache : /tmp/dhcp-dyndns.cc
# /etc/dhcpduser.keytab
TESTUSER="$($WBINFO -u | grep 'dhcpduser')"
# krbcc ticket cache
if [ -z "${TESTUSER}" ]
# /tmp/dhcp-dyndns.cc
then
logger "No AD dhcp user exists, need to create it first.. exiting."
TESTUSER=$(wbinfo -u | grep dhcpduser)
logger "you can do this by typing the following commands"
if [ -z "${TESTUSER}" ]; then
logger "kinit Administrator@${REALM}"
echo "No AD dhcp user exists, need to create it first.. exiting."
logger "$SAMBATOOL user create dhcpduser --random-password --description='Unprivileged user for DNS updates via ISC DHCP server'"
echo "you can do this by typing the following commands"
logger "$SAMBATOOL user setexpiry dhcpduser --noexpiry"
echo "kinit Administrator@${REALM}"
logger "$SAMBATOOL group addmembers DnsAdmins dhcpduser"
echo "samba-tool user create dhcpduser --random-password --description=\"Unprivileged user for DNS updates via ISC DHCP server\""
exit 1
echo "samba-tool user setexpiry dhcpduser --noexpiry"
echo "samba-tool group addmembers DnsAdmins dhcpduser"
exit 1
fi
fi
# Check for Kerberos keytab
# Check for Kerberos keytab
if [ ! -f /etc/dhcp/dhcpduser.keytab ]; then
if [ ! -f "$keytab" ]
then
echo "Required keytab /etc/dhcpduser.keytab not found, it needs to be created."
logger "Required keytab $keytab not found, it needs to be created."
echo "Use the following commands as root"
logger "Use the following commands as root"
echo "samba-tool domain exportkeytab --principal=${SETPRINCIPAL} /etc/dhcpduser.keytab"
logger "$SAMBATOOL domain exportkeytab --principal=${SETPRINCIPAL} $keytab"
echo "chown dhcpd:dhcpd /etc/dhcpduser.keytab"
echo "chmod 400 /etc/dhcpduser.keytab"
logger "chown XXXX:XXXX $keytab"
logger "Replace 'XXXX:XXXX' with the user & group that dhcpd runs as on your distro"
exit 1
logger "chmod 400 $keytab"
exit 1
fi
fi
# Variables supplied by dhcpd.conf
# Variables supplied by dhcpd.conf
action=$1
action="$1"
ip=$2
ip="$2"
DHCID=$3
DHCID="$3"
name=${4%%.*}
name="${4%%.*}"
# Exit if no ip address
usage()
if [ -z "${ip}" ]
{
then
echo "USAGE:"
usage
echo " `basename $0` add ip-address dhcid|mac-address hostname"
exit 1
echo " `basename $0` delete ip-address dhcid|mac-address"
}
fi
# Exit if no computer name supplied, unless the action is 'delete'
_KERBEROS () {
if [ -z "${name}" ]
# get current time as a number
then
test=$(date +%d'-'%m'-'%y' '%H':'%M':'%S)
if [ "${action}" = "delete" ]
# Note: there have been problems with this
then
# check that 'date' returns something like
name=$(host -t PTR "${ip}" | awk '{print $NF}' | awk -F '.' '{print $1}')
# 04-09-15 09:38:14
else
usage
# Check for valid kerberos ticket
exit 1
#logger "${test} [dyndns] : Running check for valid kerberos ticket"
fi
klist -c /tmp/dhcp-dyndns.cc -s
if [ "$?" != "0" ]; then
logger "${test} [dyndns] : Getting new ticket, old one has expired"
kinit -F -k -t /etc/dhcp/dhcpduser.keytab -c /tmp/dhcp-dyndns.cc "${SETPRINCIPAL}"
if [ "$?" != "0" ]; then
logger "${test} [dyndns] : dhcpd kinit for dynamic DNS failed"
exit 1;
fi
fi
fi
# exit if name contains a space
}
case ${name} in
*\ * )
logger "Invalid hostname '${name}' ...Exiting"
exit
;;
esac
# if you want computers with a hostname that starts with 'dhcp' in AD
# Exit if no ip address or mac-address
# comment the following block of code.
if [ -z "${ip}" ] || [ -z "${DHCID}" ]; then
<nowiki>if [[ $name == dhcp* ]]</nowiki>
usage
then
exit 1
logger "not updating DNS record in AD, invalid name"
exit 0
fi
fi
## update ##
# Exit if no computer name supplied, unless the action is 'delete'
if [ "${name}" = "" ]; then
case "${action}" in
add)
if [ "${action}" = "delete" ]; then
_KERBEROS
name=$(host -t PTR "${ip}" | awk '{print $NF}' | awk -F '.' '{print $1}')
count=0
else
# does host have an existing 'A' record ?
usage
mapfile -t A_REC < <($SAMBATOOL dns query "${Server}" "${domain}" "${name}" A "$KTYPE" 2>/dev/null | grep 'A:' | awk '{print $2}')
exit 1;
if [ "${#A_REC[@]}" -eq 0 ]
fi
then
fi
# no A record to delete
result1=0
$SAMBATOOL dns add "${Server}" "${domain}" "${name}" A "${ip}" "$KTYPE"
result2="$?"
elif [ "${#A_REC[@]}" -gt 1 ]
then
for i in "${A_REC[@]}"
do
$SAMBATOOL dns delete "${Server}" "${domain}" "${name}" A "${i}" "$KTYPE"
done
# all A records deleted
result1=0
$SAMBATOOL dns add "${Server}" "${domain}" "${name}" A "${ip}" "$KTYPE"
result2="$?"
elif [ "${#A_REC[@]}" -eq 1 ]
then
# turn array into a variable
VAR_A_REC="${A_REC[*]}"
if [ "$VAR_A_REC" = "${ip}" ]
then
# Correct A record exists, do nothing
logger "Correct 'A' record exists, not updating."
result1=0
result2=0
count=$((count+1))
elif [ "$VAR_A_REC" != "${ip}" ]
then
# Wrong A record exists
logger "'A' record changed, updating record."
$SAMBATOOL dns delete "${Server}" "${domain}" "${name}" A "${VAR_A_REC}" "$KTYPE"
result1="$?"
$SAMBATOOL dns add "${Server}" "${domain}" "${name}" A "${ip}" "$KTYPE"
result2="$?"
fi
fi
# get existing reverse zones (if any)
# Set PTR address
ReverseZones=$($SAMBATOOL dns zonelist "${Server}" "$KTYPE" --reverse | grep 'pszZoneName' | awk '{print $NF}')
ptr=$(echo ${ip} | awk -F '.' '{print $4"."$3"."$2"."$1".in-addr.arpa"}')
if [ -z "$ReverseZones" ]; then
logger "No reverse zone found, not updating"
result3='0'
result4='0'
count=$((count+1))
else
for revzone in $ReverseZones
do
rev_zone_info "$revzone" "${ip}"
if [[ ${ip} = $ZoneIP* ]] && [ "$ZoneIP" = "$RZIP" ]
then
# does host have an existing 'PTR' record ?
PTR_REC=$($SAMBATOOL dns query "${Server}" "${revzone}" "${IP2add}" PTR "$KTYPE" 2>/dev/null | grep 'PTR:' | awk '{print $2}' | awk -F '.' '{print $1}')
<nowiki>if [[ -z $PTR_REC ]]</nowiki>
then
# no PTR record to delete
result3=0
$SAMBATOOL dns add "${Server}" "${revzone}" "${IP2add}" PTR "${name}"."${domain}" "$KTYPE"
result4="$?"
break
elif [ "$PTR_REC" = "${name}" ]
then
# Correct PTR record exists, do nothing
logger "Correct 'PTR' record exists, not updating."
result3=0
result4=0
count=$((count+1))
break
elif [ "$PTR_REC" != "${name}" ]
then
# Wrong PTR record exists
# points to wrong host
logger "'PTR' record changed, updating record."
$SAMBATOOL dns delete "${Server}" "${revzone}" "${IP2add}" PTR "${PTR_REC}"."${domain}" "$KTYPE"
result3="$?"
$SAMBATOOL dns add "${Server}" "${revzone}" "${IP2add}" PTR "${name}"."${domain}" "$KTYPE"
result4="$?"
break
fi
else
continue
fi
done
fi
;;
delete)
_KERBEROS
count=0
## nsupdate ##
$SAMBATOOL dns delete "${Server}" "${domain}" "${name}" A "${ip}" "$KTYPE"
result1="$?"
# get existing reverse zones (if any)
ReverseZones=$($SAMBATOOL dns zonelist "${Server}" --reverse "$KTYPE" | grep 'pszZoneName' | awk '{print $NF}')
if [ -z "$ReverseZones" ]
then
logger "No reverse zone found, not updating"
result2='0'
count=$((count+1))
else
for revzone in $ReverseZones
do
rev_zone_info "$revzone" "${ip}"
if [[ ${ip} = $ZoneIP* ]] && [ "$ZoneIP" = "$RZIP" ]
then
host -t PTR "${ip}" > /dev/null 2>&1
ret="$?"
if [ $ret -eq 0 ]
then
$SAMBATOOL dns delete "${Server}" "${revzone}" "${IP2add}" PTR "${name}"."${domain}" "$KTYPE"
result2="$?"
else
result2='0'
count=$((count+1))
fi
break
else
continue
fi
done
fi
result3='0'
result4='0'
;;
*)
logger "Invalid action specified"
exit 103
;;
esac
result="${result1}:${result2}:${result3}:${result4}"
case "${action}" in
add)
_KERBEROS
if [ "$count" -eq 0 ]
nsupdate -g ${NSUPDFLAGS} << UPDATE
then
server 127.0.0.1
if [ "${result}" != "0:0:0:0" ]
realm ${REALM}
then
update delete ${name}.${domain} 3600 A
logger "DHCP-DNS $action failed: ${result}"
update add ${name}.${domain} 3600 A ${ip}
exit 1
send
else
UPDATE
logger "DHCP-DNS $action succeeded"
result1=$?
fi
fi
if [ "$Add_macAddress" != 'no' ]
nsupdate -g ${NSUPDFLAGS} << UPDATE
then
server 127.0.0.1
if [ -n "$DHCID" ]
realm ${REALM}
then
update delete ${ptr} 3600 PTR
Computer_Object=$(ldbsearch "$KTYPE" -H ldap://"$Server" "(&(objectclass=computer)(objectclass=ieee802Device)(cn=$name))" | grep -v '#' | grep -v 'ref:')
update add ${ptr} 3600 PTR ${name}.${domain}
if [ -z "$Computer_Object" ]
send
then
UPDATE
# Computer object not found with the 'ieee802Device' objectclass, does the computer actually exist, it should.
result2=$?
Computer_Object=$(ldbsearch "$KTYPE" -H ldap://"$Server" "(&(objectclass=computer)(cn=$name))" | grep -v '#' | grep -v 'ref:')
;;
if [ -z "$Computer_Object" ]
delete)
then
_KERBEROS
logger "Computer '$name' not found. Exiting."
exit 68
else
DN=$(echo "$Computer_Object" | grep 'dn:')
objldif="$DN
changetype: modify
add: objectclass
objectclass: ieee802Device"
attrldif="$DN
nsupdate -g ${NSUPDFLAGS} << UPDATE
changetype: modify
server 127.0.0.1
add: macAddress
realm ${REALM}
macAddress: $DHCID"
update delete ${name}.${domain} 3600 A
send
UPDATE
result1=$?
nsupdate -g ${NSUPDFLAGS} << UPDATE
server 127.0.0.1
realm ${REALM}
update delete ${ptr} 3600 PTR
send
UPDATE
result2=$?
;;
*)
echo "Invalid action specified"
exit 103
;;
esac
# add the ldif
result="${result1}${result2}"
echo "$objldif" | ldbmodify "$KTYPE" -H ldap://"$Server"
ret="$?"
if [ $ret -ne 0 ]
then
logger "Error modifying Computer objectclass $name in AD."
exit "${ret}"
fi
sleep 2
echo "$attrldif" | ldbmodify "$KTYPE" -H ldap://"$Server"
ret="$?"
if [ "$ret" -ne 0 ]; then
logger "Error modifying Computer attribute $name in AD."
exit "${ret}"
fi
unset objldif
unset attrldif
logger "Successfully modified Computer $name in AD"
fi
else
DN=$(echo "$Computer_Object" | grep 'dn:')
attrldif="$DN
changetype: modify
replace: macAddress
macAddress: $DHCID"
echo "$attrldif" | ldbmodify "$KTYPE" -H ldap://"$Server"
if [ "${result}" != "00" ]; then
ret="$?"
logger "DHCP-DNS Update failed: ${result}"
if [ "$ret" -ne 0 ]
else
then
logger "DHCP-DNS Update succeeded"
logger "Error modifying Computer attribute $name in AD."
exit "${ret}"
fi
unset attrldif
logger "Successfully modified Computer $name in AD"
fi
fi
fi
fi
exit ${result}
exit 0




If you wish to store the computers MAC address in AD, find this line:

Add_macAddress='no'

It is near the top of the script. Change 'no' to 'yes'. Note you will need to grant DomainAdmin privileges to the DNS update user.




Set the permissions on the script.
Set the permissions on the script.


# chmod 755 /etc/dhcp/bin/dhcp-dyndns.sh
# chmod 755 /usr/local/bin/dhcp-dyndns.sh






Line 258: Line 546:
option domain-name "samdom.example.com";
option domain-name "samdom.example.com";
option domain-name-servers 192.168.0.6, 192.168.0.5;
option domain-name-servers 192.168.0.6, 192.168.0.5;
option netbios-name-servers 192.168.0.5, 192.168.0.6;
option ntp-servers 192.168.0.5, 192.168.0.6;
option ntp-servers 192.168.0.5, 192.168.0.6;
pool {
pool {
Line 269: Line 556:
set noname = concat("dhcp-", binary-to-ascii(10, 8, "-", leased-address));
set noname = concat("dhcp-", binary-to-ascii(10, 8, "-", leased-address));
set ClientIP = binary-to-ascii(10, 8, ".", leased-address);
set ClientIP = binary-to-ascii(10, 8, ".", leased-address);
set ClientDHCID = binary-to-ascii(16, 8, ":", hardware);
set ClientDHCID = concat (
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,1,1))),2), ":",
set ClientName = pick-first-value(option host-name, config-option-host-name, client-name, noname);
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,2,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,3,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,4,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,5,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,6,1))),2)
);
set ClientName = pick-first-value(option host-name, config-option host-name, client-name, noname);
log(concat("Commit: IP: ", ClientIP, " DHCID: ", ClientDHCID, " Name: ", ClientName));
log(concat("Commit: IP: ", ClientIP, " DHCID: ", ClientDHCID, " Name: ", ClientName));
execute("/etc/dhcp/bin/dhcp-dyndns.sh", "add", ClientIP, ClientDHCID, ClientName);
execute("/usr/local/bin/dhcp-dyndns.sh", "add", ClientIP, ClientDHCID, ClientName);
}
}
on release {
on release {
set ClientIP = binary-to-ascii(10, 8, ".", leased-address);
set ClientIP = binary-to-ascii(10, 8, ".", leased-address);
set ClientDHCID = binary-to-ascii(16, 8, ":", hardware);
set ClientDHCID = concat (
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,1,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,2,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,3,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,4,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,5,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,6,1))),2)
);
log(concat("Release: IP: ", ClientIP));
log(concat("Release: IP: ", ClientIP));
execute("/etc/dhcp/bin/dhcp-dyndns.sh", "delete", ClientIP, ClientDHCID);
execute("/usr/local/bin/dhcp-dyndns.sh", "delete", ClientIP, ClientDHCID);
}
}
Line 287: Line 588:
log(concat("Expired: IP: ", ClientIP));
log(concat("Expired: IP: ", ClientIP));
# cannot get a ClientName here, for some reason that always fails
# cannot get a ClientName here, for some reason that always fails
# however the dhcp update script will obtain the short hostname.
execute("/etc/dhcp/bin/dhcp-dyndns.sh", "delete", ClientIP, "", "0");
execute("/usr/local/bin/dhcp-dyndns.sh", "delete", ClientIP, "", "0");
}
}






Start the dhcp server and see what happens, don't forget to stop your windows clients trying to update their own records, as this will fail.
Start the dhcp server and see what happens.


: {{Imbox
| type = important
| text = You must stop your windows clients from trying to update their own records, as this will fail and fill your logs with errors.
}}




Line 298: Line 606:
= Add failover =
= Add failover =


Add the following for the failover peers to the /etc/dhcp/dhcpd.conf file on the primary:
Add the following to the /etc/dhcp/dhcpd.conf file on the primary:


failover peer "dhcp-failover" {
failover peer "dhcp-failover" {
primary;
primary;
address dc1.samdom.example.com;
address dc1.samdom.example.com;
port 519;
peer address dc2.samdom.example.com;
peer address dc2.samdom.example.com;
peer port 520;
max-response-delay 60;
max-response-delay 60;
max-unacked-updates 10;
max-unacked-updates 10;
mclt 3600;
mclt 3600;
split 128;
split 255;
load balance max seconds 3;
load balance max seconds 3;
}
}
Line 318: Line 624:
secondary;
secondary;
address dc2.samdom.example.com;
address dc2.samdom.example.com;
port 520;
peer address dc1.samdom.example.com;
peer address dc1.samdom.example.com;
peer port 519;
max-response-delay 60;
max-response-delay 60;
max-unacked-updates 10;
max-unacked-updates 10;
load balance max seconds 3;
load balance max seconds 3;
}
}

: {{Imbox
| type = important
| text = Make sure that you add the failover section, above the 'subnet' section.
}}



Add references for the subnet/pool which will do failover.
Add references for the subnet/pool which will do failover.
Line 343: Line 653:
}
}


Configure OMAPI and define a secret key.
== Configure OMAPI and Define a Secret Key ==

=== BIND 9.12 and earlier ===


Generate a random OMAPI key on the primary, using the dnssec-keygen utility distributed with BIND.
Generate a random OMAPI key on the primary, using the dnssec-keygen utility distributed with BIND.
Line 357: Line 669:
omapi-port 7911;
omapi-port 7911;
omapi-key omapi_key;
omapi-key omapi_key;

key omapi_key {
key omapi_key {
algorithm hmac-md5;
algorithm hmac-md5;
Line 363: Line 675:
}
}


Replace PUT_YOUR_KEY_HERE with the key you extracted from the private key created by the dnssec command
Replace PUT_YOUR_KEY_HERE with the key you extracted from the private key created by the dnssec command.


Continue with [[#All BIND versions]]

=== BIND 9.13 and later ===

Generate a random OMAPI key on either primary or secondary, using the tsig-keygen utility distributed with BIND.

tsig-keygen -a hmac-md5 omapi_key

The command will output text to your screen, similar to this:

key "omapi_key" {
algorithm hmac-md5;
secret "some_secret_text";
};

Add the following lines to dhcpd.conf on both primary and secondary, followed by the text from the previous command:

omapi-port 7911;
omapi-key omapi_key;

key "omapi_key" {
algorithm hmac-md5;
secret "some_secret_text";
};

Continue with [[#All BIND versions]]

=== All BIND versions ===


Restart both servers to apply the configuration changes.
Restart both servers to apply the configuration changes.

You should find lines similar to these, in the system logs on both machines:

Feb 28 17:34:39 dc1 dhcpd: failover peer dhcp-failover: peer moves from recover-done to normal
Feb 28 17:34:39 dc1 dhcpd: failover peer dhcp-failover: Both servers normal


If OMAPI is working properly you can test failover by stopping the primary server.
If OMAPI is working properly you can test failover by stopping the primary server.

If you are using a firewall, you will need to open TCP ports 647 and 7911


Once you are sure everything is working as expected, restart both servers to ensure everything is running correctly.
Once you are sure everything is working as expected, restart both servers to ensure everything is running correctly.


The 'split' value '128' divides responsibility for the clients between the two failover partners.
The 'split' value '255' on the 'primary', makes it responsible for the clients.
If you want the primary to answer all dhcp requests unless it is down (for whatever reason) set the value to '255', use '0' to make the secondary responsible.
With the value set to '255', the primary will answer all dhcp requests unless it is down (for whatever reason), use '0' to make the secondary responsible.

For more information, read the dhcpd.conf manpage <code>man dhcpd.conf</code>.





= Apparmor =

To get DHCP updates working with Apparmor, you need to alter /etc/apparmor.d/usr.sbin.dhcpd to match this.

/etc/dhcp/ r,
/etc/dhcp/** r,
/etc/dhcpd{,6}.conf r,
/etc/dhcpd{,6}_ldap.conf r,
/usr/local/bin/dhcp-dyndns.sh ix,
/bin/grep rix,
/usr/sbin/samba rix,
/usr/bin/gawk rix,
/bin/hostname rix,
/usr/bin/wbinfo rix,
/usr/bin/heimtools rix,
/usr/bin/logger rix,
/usr/bin/kinit.heimdal rix,
/bin/date rix,
/dev/tty wr,
/dev/urandom w,
/proc/** r,
/usr/bin/kinit w,
/run/samba/winbindd/pipe wr,



The first 4 lines are the default, you will need to add everything else.
With these settings the dhcp-server will start and work.

The above settings have been tested on Ubuntu 18.04 and were supplied by Stefan Kania.




Any questions or problems, ask on the Samba mailing list.
Any questions or problems, ask on the Samba mailing list.
{{Imbox
| type = note
| text = Do not log a bug report on Samba bugzilla for any problems you have with this set up, ask on the samba mailing list.
}}



----
[[Category:Active Directory]]
[[Category:DNS]]

Latest revision as of 13:11, 11 August 2023

Introduction

This HowTo describes how to configure isc DHCP to update Samba dns records in AD.

It has now been tested with the Samba AD internal DNS server and BIND9_DLZ.

This HowTo is based on a Debian OS install, the paths given may be different if you use another OS.

The script has now been modified to use samba-tool instead of nsupdate, it also can optionally add the macAddress attribute to a computers AD object, this attribute will contain the computers MAC address.


Preconditions

  • The computer has been provisioned as an AD DC and the samba, smbd and winbindd daemons are running.
  • You have created any required reverse zones.
  • You are logged into the DC as 'root'
  • If using Bind9, Bind9_dlz must be installed and working on the Samba AD DC that you are doing this on. Tested with various 9.x versions.


Names and Addresses used in this howto

  • Realm  : SAMDOM.EXAMPLE.COM
  • Subnet  : 192.168.0.0
  • Netmask  : 255.255.255.0
  • Subnet-mask  : 255.255.255.0
  • Broadcast-address  : 192.168.0.255
  • Gateway  : 192.168.0.1
  • Domain-name  : samdom.example.com
  • Domain-name-servers  : 192.168.0.6, 192.168.0.5
  • Netbios-name-servers : 192.168.0.5, 192.168.0.6
  • Ntp-servers  : 192.168.0.5, 192.168.0.6;
  • Pool range  : 192.168.0.50 192.168.0.229


Install isc DHCP

First install the DHCP server

# apt-get install isc-dhcp-server

Or on FreeBSD:

# pkg install isc-dhcp44-server

Create a user to carry out the updates

You need a user that the script will run as, set a random password because you will never logon as the user.

# samba-tool user create dhcpduser --description="Unprivileged user for TSIG-GSSAPI DNS updates via ISC DHCP server" --random-password

Now set the users password to never expire and add the user to the DnsAdmins group.

# samba-tool user setexpiry dhcpduser --noexpiry
# samba-tool group addmembers DnsAdmins dhcpduser

Now export the required keytab. On FreeBSD change /etc/dhcpduser.keytab to /usr/local/etc/dhcpduser.keytab

# samba-tool domain exportkeytab --principal=dhcpduser@SAMDOM.EXAMPLE.COM /etc/dhcpduser.keytab
# chown root:root  /etc/dhcpduser.keytab
# chmod 400  /etc/dhcpduser.keytab


Create the script for the updates

Copy this script to /usr/local/bin/dhcp-dyndns.sh

#!/bin/bash
# On FreeBSD change the above line to #!/usr/local/bin/bash
#
# /usr/local/bin/dhcp-dyndns.sh
#
# This script is for secure DDNS updates on Samba,
# it can also add the 'macAddress' to the Computers object.
#
# Version: 0.9.6
#
# Copyright (C) Rowland Penny 2020-2022
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

# You may need to ensure that you have a useful path
# If you have 'path' problems, Uncomment the next line and adjust for
# your setup e.g. self-compiled Samba
#export PATH=/usr/local/samba/bin:/usr/local/samba/sbin:/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin

##########################################################################
#                                                                        #
#    You can optionally add the 'macAddress' to the Computers object.    #
#    Add 'dhcpduser' to the 'Domain Admins' group if used                #
#    Change the next line to 'yes' to make this happen                   #
Add_macAddress='no'
#                                                                        #
##########################################################################

# On FreeBSD change this to /usr/local/etc/dhcpduser.keytab
keytab=/etc/dhcpduser.keytab

usage()
{
	cat <<-EOF
	USAGE:
	  $(basename "$0") add ip-address dhcid|mac-address hostname
	  $(basename "$0") delete ip-address dhcid|mac-address
	EOF
}

_KERBEROS()
{
	# get current time as a number
	test=$(date +%d'-'%m'-'%y' '%H':'%M':'%S)
	# Note: there have been problems with this
	# check that 'date' returns something like

	# Check for valid kerberos ticket
	#logger "${test} [dyndns] : Running check for valid kerberos ticket"
	klist -c "${KRB5CCNAME}" -s
	ret="$?"
	if [ $ret -ne 0 ]
	then
		logger "${test} [dyndns] : Getting new ticket, old one has expired"
		# On FreeBSD change the -F to --no-forwardable
		kinit -F -k -t $keytab "${SETPRINCIPAL}"
		ret="$?"
		if [ $ret -ne 0 ]
		then
			logger "${test} [dyndns] : dhcpd kinit for dynamic DNS failed"
			exit 1
		fi
	fi
}

rev_zone_info()
{
	local RevZone="$1"
	local IP="$2"
	local rzoneip
	rzoneip="${RevZone%.in-addr.arpa}"
	local rzonenum
	rzonenum=$(echo "$rzoneip" |  tr '.' '\n')
	declare -a words
	for n in $rzonenum
	do
		words+=("$n")
	done
	local numwords="${#words[@]}"

	unset ZoneIP
	unset RZIP
	unset IP2add

	case "$numwords" in
		1)
			# single ip rev zone '192'
			ZoneIP=$(echo "${IP}" | awk -F '.' '{print $1}')
			RZIP="${rzoneip}"
			IP2add=$(echo "${IP}" | awk -F '.' '{print $4"."$3"."$2}')
			;;
		2)
			# double ip rev zone '168.192'
			ZoneIP=$(echo "${IP}" | awk -F '.' '{print $1"."$2}')
			RZIP=$(echo "${rzoneip}" | awk -F '.' '{print $2"."$1}')
			IP2add=$(echo "${IP}" | awk -F '.' '{print $4"."$3}')
			;;
		3)
			# triple ip rev zone '0.168.192'
			ZoneIP=$(echo "${IP}" | awk -F '.' '{print $1"."$2"."$3}')
			RZIP=$(echo "${rzoneip}" | awk -F '.' '{print $3"."$2"."$1}')
			IP2add=$(echo "${IP}" | awk -F '.' '{print $4}')
			;;
		*)
			# should never happen
			exit 1
			;;
	esac
}

BINDIR=$(samba -b | grep 'BINDIR' | grep -v 'SBINDIR' | awk '{print $NF}')
[[ -z $BINDIR ]] && printf "Cannot find the 'samba' binary, is it installed ?\\nOr is your path set correctly ?\\n"
WBINFO="$BINDIR/wbinfo"

SAMBATOOL=$(command -v samba-tool)
[[ -z $SAMBATOOL ]] && printf "Cannot find the 'samba-tool' binary, is it installed ?\\nOr is your path set correctly ?\\n"

MINVER=$($SAMBATOOL -V | grep -o '[0-9]*' | tr '\n' ' ' | awk '{print $2}')
if [ "$MINVER" -gt '14' ]
then
	KTYPE="--use-kerberos=required"
else
	KTYPE="-k yes"
fi

# DHCP Server hostname
Server=$(hostname -s)

# DNS domain
domain=$(hostname -d)
if [ -z "${domain}" ]
then
	logger "Cannot obtain domain name, is DNS set up correctly?"
	logger "Cannot continue... Exiting."
	exit 1
fi

# Samba realm
REALM="${domain^^}"

# krbcc ticket cache
export KRB5CCNAME="/tmp/dhcp-dyndns.cc"

# Kerberos principal
SETPRINCIPAL="dhcpduser@${REALM}"
# Kerberos keytab as above
# krbcc ticket cache : /tmp/dhcp-dyndns.cc
TESTUSER="$($WBINFO -u | grep 'dhcpduser')"
if [ -z "${TESTUSER}" ]
then
	logger "No AD dhcp user exists, need to create it first.. exiting."
	logger "you can do this by typing the following commands"
	logger "kinit Administrator@${REALM}"
	logger "$SAMBATOOL user create dhcpduser --random-password --description='Unprivileged user for DNS updates via ISC DHCP server'"
	logger "$SAMBATOOL user setexpiry dhcpduser --noexpiry"
	logger "$SAMBATOOL group addmembers DnsAdmins dhcpduser"
	exit 1
fi

# Check for Kerberos keytab
if [ ! -f "$keytab" ]
then
	logger "Required keytab $keytab not found, it needs to be created."
	logger "Use the following commands as root"
	logger "$SAMBATOOL domain exportkeytab --principal=${SETPRINCIPAL} $keytab"
	logger "chown XXXX:XXXX $keytab"
	logger "Replace 'XXXX:XXXX' with the user & group that dhcpd runs as on your distro"
	logger "chmod 400 $keytab"
	exit 1
fi

# Variables supplied by dhcpd.conf
action="$1"
ip="$2"
DHCID="$3"
name="${4%%.*}"

# Exit if no ip address
if [ -z "${ip}" ]
then
	usage
	exit 1
fi

# Exit if no computer name supplied, unless the action is 'delete'
if [ -z "${name}" ]
then
	if [ "${action}" = "delete" ]
	then
		name=$(host -t PTR "${ip}" | awk '{print $NF}' | awk -F '.' '{print $1}')
	else
		usage
		exit 1
	fi
fi

# exit if name contains a space
case ${name} in
	*\ * )
		logger "Invalid hostname '${name}' ...Exiting"
		exit
		;;
esac

# if you want computers with a hostname that starts with 'dhcp' in AD
# comment the following block of code.
if [[ $name == dhcp* ]]
then
	logger "not updating DNS record in AD, invalid name"
	exit 0
fi

## update ##
case "${action}" in
	add)
		_KERBEROS
		count=0
		# does host have an existing 'A' record ?
		mapfile -t A_REC < <($SAMBATOOL dns query "${Server}" "${domain}" "${name}" A "$KTYPE" 2>/dev/null | grep 'A:' | awk '{print $2}')
		if [ "${#A_REC[@]}" -eq 0 ]
		then
			# no A record to delete
			result1=0
			$SAMBATOOL dns add "${Server}" "${domain}" "${name}" A "${ip}" "$KTYPE"
			result2="$?"
		elif [ "${#A_REC[@]}" -gt 1 ]
		then
			for i in "${A_REC[@]}"
			do
				$SAMBATOOL dns delete "${Server}" "${domain}" "${name}" A "${i}" "$KTYPE"
			done
			# all A records deleted
			result1=0
			$SAMBATOOL dns add "${Server}" "${domain}" "${name}" A "${ip}" "$KTYPE"
			result2="$?"
		elif [ "${#A_REC[@]}" -eq 1 ]
		then
			# turn array into a variable
			VAR_A_REC="${A_REC[*]}"
			if [ "$VAR_A_REC" = "${ip}" ]
			then
				# Correct A record exists, do nothing
				logger "Correct 'A' record exists, not updating."
				result1=0
				result2=0
				count=$((count+1))
			elif [ "$VAR_A_REC" != "${ip}" ]
			then
				# Wrong A record exists
				logger "'A' record changed, updating record."
				$SAMBATOOL dns delete "${Server}" "${domain}" "${name}" A "${VAR_A_REC}" "$KTYPE"
				result1="$?"
				$SAMBATOOL dns add "${Server}" "${domain}" "${name}" A "${ip}" "$KTYPE"
				result2="$?"
			fi
		fi

		# get existing reverse zones (if any)
		ReverseZones=$($SAMBATOOL dns zonelist "${Server}" "$KTYPE" --reverse | grep 'pszZoneName' | awk '{print $NF}')
		if [ -z "$ReverseZones" ]; then
			logger "No reverse zone found, not updating"
			result3='0'
			result4='0'
			count=$((count+1))
		else
			for revzone in $ReverseZones
			do
				rev_zone_info "$revzone" "${ip}"
				if [[ ${ip} = $ZoneIP* ]] && [ "$ZoneIP" = "$RZIP" ]
				then
					# does host have an existing 'PTR' record ?
					PTR_REC=$($SAMBATOOL dns query "${Server}" "${revzone}" "${IP2add}" PTR "$KTYPE" 2>/dev/null | grep 'PTR:' | awk '{print $2}' | awk -F '.' '{print $1}')
					if [[ -z $PTR_REC ]]
					then
						# no PTR record to delete
						result3=0
						$SAMBATOOL dns add "${Server}" "${revzone}" "${IP2add}" PTR "${name}"."${domain}" "$KTYPE"
						result4="$?"
						break
					elif [ "$PTR_REC" = "${name}" ]
					then
						# Correct PTR record exists, do nothing
						logger "Correct 'PTR' record exists, not updating."
						result3=0
						result4=0
						count=$((count+1))
						break
					elif [ "$PTR_REC" != "${name}" ]
					then
						# Wrong PTR record exists
						# points to wrong host
						logger "'PTR' record changed, updating record."
						$SAMBATOOL dns delete "${Server}" "${revzone}" "${IP2add}" PTR "${PTR_REC}"."${domain}" "$KTYPE"
						result3="$?"
						$SAMBATOOL dns add "${Server}" "${revzone}" "${IP2add}" PTR "${name}"."${domain}" "$KTYPE"
						result4="$?"
						break
					fi
				else
					continue
				fi
			done
	        fi
		;;
	delete)
		_KERBEROS

		count=0
		$SAMBATOOL dns delete "${Server}" "${domain}" "${name}" A "${ip}" "$KTYPE"
		result1="$?"
		# get existing reverse zones (if any)
		ReverseZones=$($SAMBATOOL dns zonelist "${Server}" --reverse "$KTYPE" | grep 'pszZoneName' | awk '{print $NF}')
		if [ -z "$ReverseZones" ]
		then
			logger "No reverse zone found, not updating"
			result2='0'
			count=$((count+1))
		else
			for revzone in $ReverseZones
			do
				rev_zone_info "$revzone" "${ip}"
				if [[ ${ip} = $ZoneIP* ]] && [ "$ZoneIP" = "$RZIP" ]
				then
					host -t PTR "${ip}" > /dev/null 2>&1
					ret="$?"
					if [ $ret -eq 0 ]
					then
						$SAMBATOOL dns delete "${Server}" "${revzone}" "${IP2add}" PTR "${name}"."${domain}" "$KTYPE"
						result2="$?"
					else
						result2='0'
						count=$((count+1))
					fi
					break
				else
					continue
				fi
			done
		fi
		result3='0'
		result4='0'
		;;
	*)
		logger "Invalid action specified"
		exit 103
	;;
esac

result="${result1}:${result2}:${result3}:${result4}"

if [ "$count" -eq 0 ]
then
	if [ "${result}" != "0:0:0:0" ]
	then
		logger "DHCP-DNS $action failed: ${result}"
		exit 1
	else
		logger "DHCP-DNS $action succeeded"
	fi
fi

if [ "$Add_macAddress" != 'no' ]
then
	if [ -n "$DHCID" ]
	then
		Computer_Object=$(ldbsearch "$KTYPE" -H ldap://"$Server" "(&(objectclass=computer)(objectclass=ieee802Device)(cn=$name))" | grep -v '#' | grep -v 'ref:')
		if [ -z "$Computer_Object" ]
		then
			# Computer object not found with the 'ieee802Device' objectclass, does the computer actually exist, it should.
			Computer_Object=$(ldbsearch "$KTYPE" -H ldap://"$Server" "(&(objectclass=computer)(cn=$name))" | grep -v '#' | grep -v 'ref:')
			if [ -z "$Computer_Object" ]
			then
				logger "Computer '$name' not found. Exiting."
				exit 68
			else
				DN=$(echo "$Computer_Object" | grep 'dn:')
				objldif="$DN
changetype: modify
add: objectclass
objectclass: ieee802Device"

				attrldif="$DN
changetype: modify
add: macAddress
macAddress: $DHCID"

				# add the ldif
				echo "$objldif" | ldbmodify "$KTYPE" -H ldap://"$Server"
				ret="$?"
				if [ $ret -ne 0 ]
				then
					logger "Error modifying Computer objectclass $name in AD."
					exit "${ret}"
				fi
				sleep 2
				echo "$attrldif" | ldbmodify "$KTYPE" -H ldap://"$Server"
				ret="$?"
				if [ "$ret" -ne 0 ]; then
					logger "Error modifying Computer attribute $name in AD."
					exit "${ret}"
				fi
				unset objldif
				unset attrldif
				logger "Successfully modified Computer $name in AD"
			fi
	else
		DN=$(echo "$Computer_Object" | grep 'dn:')
		attrldif="$DN
changetype: modify
replace: macAddress
macAddress: $DHCID"

		echo "$attrldif" | ldbmodify "$KTYPE" -H ldap://"$Server"
		ret="$?"
		if [ "$ret" -ne 0 ]
		then
			logger "Error modifying Computer attribute $name in AD."
			exit "${ret}"
		fi
			unset attrldif
			logger "Successfully modified Computer $name in AD"
		fi
	fi
fi

exit 0


If you wish to store the computers MAC address in AD, find this line:

Add_macAddress='no'

It is near the top of the script. Change 'no' to 'yes'. Note you will need to grant DomainAdmin privileges to the DNS update user.


Set the permissions on the script.

# chmod 755 /usr/local/bin/dhcp-dyndns.sh



Modify the dhcp conf file

First backup the original conf file.

# cp /etc/dhcp/dhcpd.conf /etc/dhcp/dhcpd.conf.orig

Now edit /etc/dhcp/dhcpd.conf and make it look similar to the this.

authoritative;
ddns-update-style none;

subnet 192.168.0.0 netmask 255.255.255.0 {
  option subnet-mask 255.255.255.0;
  option broadcast-address 192.168.0.255;
  option time-offset 0;
  option routers 192.168.0.1;
  option domain-name "samdom.example.com";
  option domain-name-servers 192.168.0.6, 192.168.0.5;
  option ntp-servers 192.168.0.5, 192.168.0.6;
  pool {
    max-lease-time 1800; # 30 minutes
    range 192.168.0.50 192.168.0.229;
  }
}

on commit {
set noname = concat("dhcp-", binary-to-ascii(10, 8, "-", leased-address));
set ClientIP = binary-to-ascii(10, 8, ".", leased-address);
set ClientDHCID = concat (
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,1,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,2,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,3,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,4,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,5,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,6,1))),2)
);
set ClientName = pick-first-value(option host-name, config-option host-name, client-name, noname);
log(concat("Commit: IP: ", ClientIP, " DHCID: ", ClientDHCID, " Name: ", ClientName));
execute("/usr/local/bin/dhcp-dyndns.sh", "add", ClientIP, ClientDHCID, ClientName);
}

on release {
set ClientIP = binary-to-ascii(10, 8, ".", leased-address);
set ClientDHCID = concat (
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,1,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,2,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,3,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,4,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,5,1))),2), ":",
suffix (concat ("0", binary-to-ascii (16, 8, "", substring(hardware,6,1))),2)
);
log(concat("Release: IP: ", ClientIP));
execute("/usr/local/bin/dhcp-dyndns.sh", "delete", ClientIP, ClientDHCID);
}

on expiry {
set ClientIP = binary-to-ascii(10, 8, ".", leased-address);
# cannot get a ClientMac here, apparently this only works when actually receiving a packet
log(concat("Expired: IP: ", ClientIP));
# cannot get a ClientName here, for some reason that always fails
# however the dhcp update script will obtain the short hostname.
execute("/usr/local/bin/dhcp-dyndns.sh", "delete", ClientIP, "", "0");
}


Start the dhcp server and see what happens.



Add failover

Add the following to the /etc/dhcp/dhcpd.conf file on the primary:

failover peer "dhcp-failover" {
  primary;
  address dc1.samdom.example.com;
  peer address dc2.samdom.example.com;
  max-response-delay 60;
  max-unacked-updates 10;
  mclt 3600;
  split 255;
  load balance max seconds 3;
}

..and secondary:

failover peer "dhcp-failover" {
  secondary;
  address dc2.samdom.example.com;
  peer address dc1.samdom.example.com;
  max-response-delay 60;
  max-unacked-updates 10;
  load balance max seconds 3;
}


Add references for the subnet/pool which will do failover.

subnet 192.168.0.0 netmask 255.255.255.0 {
  option subnet-mask 255.255.255.0;
  option broadcast-address 192.168.0.255;
  option time-offset 0;
  option routers 192.168.0.1;
  option domain-name "samdom.example.com";
  option domain-name-servers 192.168.0.5, 192.168.0.6;
  option ntp-servers 192.168.0.5, 192.168.0.6;
  pool {
    failover peer "dhcp-failover";
    max-lease-time 1800; # 30 minutes
    range 192.168.0.50 192.168.0.229;
  }
}

Configure OMAPI and Define a Secret Key

BIND 9.12 and earlier

Generate a random OMAPI key on the primary, using the dnssec-keygen utility distributed with BIND.

dnssec‐keygen ‐a HMAC‐MD5 ‐b 512 ‐n USER DHCP_OMAPI

Now extract the actual key:

cat Kdhcp_omapi.+*.private |grep ^Key|cut -d ' ' -f2-

Add the following to dhcpd.conf on both primary and secondary.

omapi-port 7911;
omapi-key omapi_key;

key omapi_key {
     algorithm hmac-md5;
     secret "PUT_YOUR_KEY_HERE";
}

Replace PUT_YOUR_KEY_HERE with the key you extracted from the private key created by the dnssec command.

Continue with #All BIND versions

BIND 9.13 and later

Generate a random OMAPI key on either primary or secondary, using the tsig-keygen utility distributed with BIND.

tsig-keygen -a hmac-md5 omapi_key

The command will output text to your screen, similar to this:

key "omapi_key" {
    algorithm hmac-md5;
    secret "some_secret_text";
};

Add the following lines to dhcpd.conf on both primary and secondary, followed by the text from the previous command:

omapi-port 7911;
omapi-key omapi_key;
key "omapi_key" {
    algorithm hmac-md5;
    secret "some_secret_text";
};

Continue with #All BIND versions

All BIND versions

Restart both servers to apply the configuration changes.

You should find lines similar to these, in the system logs on both machines:

Feb 28 17:34:39 dc1 dhcpd: failover peer dhcp-failover: peer moves from recover-done to normal
Feb 28 17:34:39 dc1 dhcpd: failover peer dhcp-failover: Both servers normal

If OMAPI is working properly you can test failover by stopping the primary server.

If you are using a firewall, you will need to open TCP ports 647 and 7911

Once you are sure everything is working as expected, restart both servers to ensure everything is running correctly.

The 'split' value '255' on the 'primary', makes it responsible for the clients. With the value set to '255', the primary will answer all dhcp requests unless it is down (for whatever reason), use '0' to make the secondary responsible.

For more information, read the dhcpd.conf manpage man dhcpd.conf.



Apparmor

To get DHCP updates working with Apparmor, you need to alter /etc/apparmor.d/usr.sbin.dhcpd to match this.

/etc/dhcp/ r,
/etc/dhcp/** r,
/etc/dhcpd{,6}.conf r,
/etc/dhcpd{,6}_ldap.conf r,
/usr/local/bin/dhcp-dyndns.sh ix,
/bin/grep rix,
/usr/sbin/samba rix,
/usr/bin/gawk rix,
/bin/hostname rix,
/usr/bin/wbinfo rix,
/usr/bin/heimtools rix,
/usr/bin/logger rix,
/usr/bin/kinit.heimdal rix,
/bin/date rix,
/dev/tty wr,
/dev/urandom w,
/proc/** r,
/usr/bin/kinit w,
/run/samba/winbindd/pipe wr,


The first 4 lines are the default, you will need to add everything else. With these settings the dhcp-server will start and work.

The above settings have been tested on Ubuntu 18.04 and were supplied by Stefan Kania.


Any questions or problems, ask on the Samba mailing list.