We are using a dhcp server configured with isc-dhcp-server on debian 8 in a small office network. The server has two network adapters one is connected to a pppoe modem and the other is connected to the local network.


# WAN network adapter
auto dsl-provider
iface dsl-provider inet ppp
pre-up /bin/ip link set wan0 up # line maintained by pppoeconf
provider dsl-provider

auto wan0
iface wan0 inet manual

# WLAN network adapter
auto wlan1
iface wlan1 inet static


ddns-update-style none;
log-facility local7;

option subnet-mask;
option broadcast-address;
option routers;
option domain-name-servers,,;
option domain-name "altfel.local";
option netbios-name-servers;

subnet netmask {
    interface wlan1;
    deny unknown-clients;

update-static-leases true;
# hosts after this line...

To give internet access to local computers we used iptables.


# By default this script does nothing.

# Enable  access to internet
iptables --table nat -A POSTROUTING -o wan0 -j MASQUERADE
iptables --table nat -A POSTROUTING -o ppp0 -j MASQUERADE

# Black list
iptables -A FORWARD -s -j DROP
# the list continues...

If I use the options to obtain IP address and DNS server automatically on a windows computer all works ok. If I write the IP address and the DNS server then I have access to the local network but I don't have internet.

The problem is that I need to manually specify a AD DC server as preferred DNS server for the client computers. The domain server ( is added in dhcpd.conf but I cant join the domain. I can only join the domain if is manually set as preferred.

  • Your DC should be forwarding DNS queries on the local network to the internet provider DNS servers. I would drop the 193.x and 213.x domain-name-servers options. Then ensure you have DNS correctly working on your DC. – albal Aug 10 '15 at 2:22

The problem was on the AD DC server.

I had to edit smb.conf:

dns forwarder =

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