how can I give openvpn clients access to a dns server (bind9) that is located on the same machine as the openvpn server

Question

I currently have a debian server that is running an openvpn server. I also have a dns server (bind9) that I would like give allow access to by the connected openvpn clients, but I am unsure as of how to do this, I already known how to send dns options to the clients using

push "dhcp-option DNS x.x.x.x"

but I am just unsure how give the clients access to the dns server that is located on the same machine as the vpn server, so if anyone could point me in the right direction I would really appreciate it. Also in case this would have anything to do with adding rules to iptables, this is my current configuration for iptables

# Generated by iptables-save v1.4.14 on Thu Oct 18 22:05:33 2012
*nat
:PREROUTING ACCEPT [3831842:462225238]
:INPUT ACCEPT [3820049:461550908]
:OUTPUT ACCEPT [1885011:139487044]
:POSTROUTING ACCEPT [1883834:139415168]
-A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE
COMMIT
# Completed on Thu Oct 18 22:05:33 2012
# Generated by iptables-save v1.4.14 on Thu Oct 18 22:05:33 2012
*filter
:INPUT ACCEPT [45799:10669929]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [45747:10335026]
:fail2ban-apache - [0:0]
:fail2ban-apache-myadmin - [0:0]
:fail2ban-apache-noscript - [0:0]
:fail2ban-ssh - [0:0]
:fail2ban-ssh-ddos - [0:0]
:fail2ban-webserver-w00tw00t - [0:0]
-A INPUT -p tcp -m multiport --dports 80,443 -j fail2ban-apache-myadmin
-A INPUT -p tcp -m multiport --dports 80,443 -j fail2ban-webserver-w00tw00t
-A INPUT -p tcp -m multiport --dports 80,443 -j fail2ban-apache-noscript
-A INPUT -p tcp -m multiport --dports 80,443 -j fail2ban-apache
-A INPUT -p tcp -m multiport --dports 22 -j fail2ban-ssh-ddos
-A INPUT -p tcp -m multiport --dports 22 -j fail2ban-ssh
-A INPUT -i tun+ -j ACCEPT
-A INPUT -i eth0 -p tcp -m tcp --dport 3306 -j ACCEPT
-A FORWARD -i tun+ -j ACCEPT
-A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
-A fail2ban-apache -j RETURN
-A fail2ban-apache-myadmin -s 211.154.213.122/32 -j DROP
-A fail2ban-apache-myadmin -s 201.170.229.96/32 -j DROP
-A fail2ban-apache-myadmin -j RETURN
-A fail2ban-apache-noscript -j RETURN
-A fail2ban-ssh -s 76.9.59.66/32 -j DROP
-A fail2ban-ssh -s 64.13.220.73/32 -j DROP
-A fail2ban-ssh -s 203.69.139.179/32 -j DROP
-A fail2ban-ssh -s 173.10.11.146/32 -j DROP
-A fail2ban-ssh -j RETURN
-A fail2ban-ssh-ddos -j RETURN
-A fail2ban-webserver-w00tw00t -s 217.70.51.154/32 -j DROP
-A fail2ban-webserver-w00tw00t -s 86.35.242.58/32 -j DROP
-A fail2ban-webserver-w00tw00t -j RETURN
COMMIT
# Completed on Thu Oct 18 22:05:33 2012

also here is my openvpn server configuration

port 1194
proto udp
dev tun
ca ca.crt
cert server.crt
key server.key
dh dh1024.pem
server 10.8.0.0 255.255.255.0
ifconfig-pool-persist ipp.txt
keepalive 10 120
comp-lzo
user nobody
group users
persist-key
persist-tun
status /var/log/openvpn/openvpn-status.log
verb 3
push "redirect-gateway def1"
push "dhcp-option DNS 213.133.98.98"
push "dhcp-option DNS 213.133.99.99"
push "dhcp-option DNS 213.133.100.100"
client-to-client

Answer 1

I just had to tell bind9 to list on an ip address that was part of the openvpn subnet

Answer 2

I solved it by adding into my /etc/bind/named.conf.options the subnet of the openvpn in this case, my LAN is 192.168.0.xxx and openvpn is 10.8.0.xxx

listen-on port 53 { localhost; 192.168.0.0/24; 10.8.0.0/24; };
allow-query { localhost; 192.168.0.0/24; 10.8.0.0/24; };

added to my openvpn server config file /etc/openvpn/server.conf in my case 192.168.0.124 is the DNS Server address:

push "dhcp-option DOMAIN mySpecificDomain.local" 
push "dhcp-option DNS 192.168.0.124"
push "dhcp-option DNS 8.8.8.8"
push "dhcp-option DNS 8.8.4.4"

my complete /etc/bind/named.conf.options file is

options {
        directory "/var/cache/bind";

        // If there is a firewall between you and nameservers you want
        // to talk to, you may need to fix the firewall to allow multiple
        // ports to talk.  See http://www.kb.cert.org/vuls/id/800113

        // If your ISP provided one or more IP addresses for stable 
        // nameservers, you probably want to use them as forwarders.  
        // Uncomment the following block, and insert the addresses replacing 
        // the all-0's placeholder.

        forwarders {
                192.168.0.1;
                8.8.8.8;
                8.8.4.4;
        };  

        //========================================================================
        // If BIND logs error messages about the root key being expired,
        // you will need to update your keys.  See https://www.isc.org/bind-keys
        //========================================================================
        //dnssec-validation auto;

        auth-nxdomain no;    # conform to RFC1035
        listen-on-v6 { any; };

        listen-on port 53 { localhost; 192.168.0.0/24; 10.8.0.0/24; };
        allow-query { localhost; 192.168.0.0/24; 10.8.0.0/24; };
        recursion yes;
};