dhcrelay running as both DHCP and DHCPv6 relay agent on CentOS 6.2

Question

I am trying to set up a DHCP relay agent that would relay DHCP requests for both IPv4 and IPv6. I am using CentOS 6.2 and I am using the dhcrelay from the ISC DHCP implementation. I would like to set it up as a service, but the man page for dhcrelay states:

-6   Run dhcrelay as a DHCPv6 relay agent.  Incompatible with the -4 option.

-4   Run  dhcrelay as a DHCPv4/BOOTP relay agent.  This is the default mode of operation, so the argu-
     ment is not necessary, but may be specified for clarity.  Incompatible with -6.

It seems that the -6 and -4 options are incompatible. How would I still make it work for both protocols without rolling my own service wrapper for both cases?

This is the service script (/etc/init.d/dhcrelay):

#!/bin/sh
#
### BEGIN INIT INFO
# Provides: dhcrelay
# Default-Start:
# Default-Stop:
# Should-Start:
# Required-Start: $network
# Required-Stop:
# Short-Description: Start and stop the DHCP relay server
# Description: dhcrelay provides the Dynamic Host Configuration Protocol (DHCP)
#              relay server.  This is required when your DHCP server is on
#              another network segment from the clients.
### END INIT INFO
#
# The fields below are left around for legacy tools (will remove later).
#
# chkconfig: - 65 35
# description: dhcrelay provides a relay for Dynamic Host Control Protocol.
# processname: dhcrelay
# # pidfile: /var/run/dhcrelay.pid

. /etc/rc.d/init.d/functions

RETVAL=0

prog=dhcrelay
exec=/usr/sbin/dhcrelay
lockfile=/var/lock/subsys/dhcrelay
pidfile=/var/run/dhcrelay.pid
config=/etc/sysconfig/dhcrelay

# The dhcrelay daemon uses the sysconfig file for configuration information.
# There is no native configuration file for this program and you must specify
# its settings on the command line.
[ -f /etc/sysconfig/dhcrelay ] && . /etc/sysconfig/dhcrelay

configtest() {
    [ -x $exec ] || exit 5
    [ -f $config ] || exit 6
    [ -z "$DHCPSERVERS" ] && exit 6
    return 0
}

rh_status() {
    status $exec
}

rh_status_q() {
    rh_status >/dev/null 2>&1
}

start() {
    [ `id -u` -eq 0 ] || exit 4
    [ -x $exec ] || exit 5
    [ -f $config ] || exit 6

    rh_status_q && return 0

    echo -n $"Starting $prog: "
    daemon $exec $DHCRELAYARGS $([ -n "$INTERFACES" ] && for int in $INTERFACES ; do echo -n " -i $int" ; done) $DHCPSERVERS 2>/dev/null
    RETVAL=$?
    echo
    [ $RETVAL -eq 0 ] && touch $lockfile
    return $RETVAL
}

stop() {
    [ `id -u` -eq 0 ] || exit 4

    rh_status_q || return 0

    echo -n $"Shutting down $prog: "
    killproc $prog
    RETVAL=$?

    echo
    [ $RETVAL -eq 0 ] && rm -f $lockfile
    return $RETVAL
}

usage() {
    echo $"Usage: $0 {start|stop|restart|force-reload|condrestart|try-restart|configtest|status}"
}

if [ $# -gt 1 ]; then
    exit 2
fi

case "$1" in
    start)
        start
        ;;
    stop)
        stop
        ;;
    restart|force-reload)
        stop ; start
        ;;
    condrestart|try-restart)
        rh_status_q || exit 0
        stop ; start
        ;;
    reload)
        usage
        # unimplemented feature
        exit 3
        ;;
    configtest)
        configtest
        ;;
    status)
        rh_status
        ;;
    *)
        usage
        exit 2
        ;;
esac

exit $?

And the etc/sysconfig/dhcrelay:

DHCRELAYARGS="-4 153.5.240.2"
# DHCPv4 only
INTERFACES=""
# DHCPv4 only
DHCPSERVERS=""

Answer 1

Youd have to make a new init script for an additional IPv6 relay. But it is not so hard.

Copy /etc/init.d/dhcrelay to /etc/init.d/dhcrelay6

Edit /etc/init.d/dhcrelay6 to

#!/bin/sh
#
### BEGIN INIT INFO
# Provides: dhcrelay6
# Default-Start:
# Default-Stop:
# Should-Start:
# Required-Start: $network
# Required-Stop:
# Short-Description: Start and stop the DHCP relay server
# Description: dhcrelay provides the Dynamic Host Configuration Protocol (DHCP)
#              relay server.  This is required when your DHCP server is on
#              another network segment from the clients.
### END INIT INFO
#
# The fields below are left around for legacy tools (will remove later).
#
# chkconfig: - 65 35
# description: dhcrelay provides a relay for Dynamic Host Control Protocol for IPv6.
# processname: dhcrelay6
# # pidfile: /var/run/dhcrelay6.pid

. /etc/rc.d/init.d/functions

RETVAL=0

prog=dhcrelay6
exec=/usr/sbin/dhcrelay6
lockfile=/var/lock/subsys/dhcrelay6
pidfile=/var/run/dhcrelay6.pid
config=/etc/sysconfig/dhcrelay6

# The dhcrelay daemon uses the sysconfig file for configuration information.
# There is no native configuration file for this program and you must specify
# its settings on the command line.
[ -f /etc/sysconfig/dhcrelay6 ] && . /etc/sysconfig/dhcrelay6

configtest() {
    [ -x $exec ] || exit 5
    [ -f $config ] || exit 6
    [ -z "$DHCPSERVERS" ] && exit 6
    return 0
}

rh_status() {
    status $exec
}

rh_status_q() {
    rh_status >/dev/null 2>&1
}

start() {
    [ `id -u` -eq 0 ] || exit 4
    [ -x $exec ] || exit 5
    [ -f $config ] || exit 6

    rh_status_q && return 0

    echo -n $"Starting $prog: "
    daemon $exec -6 $DHCRELAYARGS $([ -n "$LOWER" ] && for int in $LOWER; do echo -n " -l $int" ; done) $([ -n "$UPPER " ] && for int in $UPPER ; do echo -n " -u $int" ; done) 2>/dev/null
    RETVAL=$?
    echo
    [ $RETVAL -eq 0 ] && touch $lockfile
    return $RETVAL
}

stop() {
    [ `id -u` -eq 0 ] || exit 4

    rh_status_q || return 0

    echo -n $"Shutting down $prog: "
    killproc $prog
    RETVAL=$?

    echo
    [ $RETVAL -eq 0 ] && rm -f $lockfile
    return $RETVAL
}

usage() {
    echo $"Usage: $0 {start|stop|restart|force-reload|condrestart|try-restart|configtest|status}"
}

if [ $# -gt 1 ]; then
    exit 2
fi

case "$1" in
    start)
        start
        ;;
    stop)
        stop
        ;;
    restart|force-reload)
        stop ; start
        ;;
    condrestart|try-restart)
        rh_status_q || exit 0
        stop ; start
        ;;
    reload)
        usage
        # unimplemented feature
        exit 3
        ;;
    configtest)
        configtest
        ;;
    status)
        rh_status
        ;;
    *)
        usage
        exit 2
        ;;
esac

exit $?

Copy /etc/sysconfig/dhcrelay to /etc/sysconfig/dhcrelay

Edit /etc/sysconfig/dhcrelay to

DHCRELAYARGS=""
# Downstream interfaces (Clients)
LOWER=""
# Upstream interfaces (Servers)
UPPER=""

Execute

ln -s /usr/sbin/dhcrelay /usr/sbin/dhcrelay6

This is necessary so the service can be stoped independent from the IPv4 relay because it doesn't use a PID-file and is stopped by basename.

This is not tested as I don't have CentOS installed but it SHOULD work. Contact me if it does not and we'll work it out.

Answer 2

You don't need to do the binary linking. You say "it doesn't use a PID-file" - so why is the pid file specified in the init script then?

In actual fact, the dhcprelay daemon spawns a pid file for ipv4 mode, and a different pid file for ipv6 mode, so you just need to specify the correct pid file in each init script, and starting and stopping each instance of the daemon (ipv4 & ipv6) will work fine.