DHCP Server May Be Sending Wrong DNS To Clients

**jlacroix** · October 9th, 2012

I have a strange issue with my DHCP server (which runs Ubuntu Server). When my client machines (also Ubuntu) connect, they get the following in /etc/resolv.conf:

Code:

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 127.0.1.1
search localnet

However, I have the following in /etc/dhcp/dhcpd.conf on the server:

Code:

default-lease-time 86400;
max-lease-time 86400;
option subnet-mask 255.255.255.0;
option broadcast-address 172.16.254.255;
option routers 172.16.254.1;
option domain-name-servers 172.16.254.5, 172.16.254.1;
option domain-name "localnet";

subnet 172.16.254.0 netmask 255.255.255.0 {
range 172.16.254.200 172.16.254.250;
}

It doesn't appear that the hosts are getting applied the DNS servers I declared. Instead, they are getting localhost as the DNS server.

**papibe** · October 9th, 2012

Hi jlacroix.

It looks like the clients are running 12.04, which it has set up by default a dnsmasq plug in.

You can see the actual name servers being used by running (known as 'upstream servers' on dnsmasq's terminology):

Code:

cat /var/run/nm-dns-dnsmasq.conf

Let us know how it goes.
Regards.

**jlacroix** · October 10th, 2012

Originally Posted by papibe

Hi jlacroix.

It looks like the clients are running 12.04, which it has set up by default a dnsmasq plug in.

You can see the actual name servers being used by running (known as 'upstream servers' on dnsmasq's terminology):

Code:

cat /var/run/nm-dns-dnsmasq.conf

Let us know how it goes.
Regards.

There is no output with that command. Why would dnsmasq be a factor? I don't use that. I have a DHCP server running Ubuntu Server 12.04.

The clients are running 12.10.

**pqwoerituytrueiwoq** · October 10th, 2012

i am not running a dhcp server at home but at my moms i am i have the dns server set under the subnet section

Code:

shared-network 224-29 {
    subnet 10.0.0.0 netmask 255.255.0.0 {
        range 10.0.0.100 10.0.0.199;
        option routers 10.0.0.1;
        option domain-name-servers 8.8.8.8,8.8.4.4;
    }
}

when i connect my laptop (running 12.10) it always gives me the right DNS server settings

**jlacroix** · October 10th, 2012

Originally Posted by pqwoerituytrueiwoq

i am not running a dhcp server at home but at my moms i am i have the dns server set under the subnet section

Code:

shared-network 224-29 {
    subnet 10.0.0.0 netmask 255.255.0.0 {
        range 10.0.0.100 10.0.0.199;
        option routers 10.0.0.1;
        option domain-name-servers 8.8.8.8,8.8.4.4;
    }
}

when i connect my laptop (running 12.10) it always gives me the right DNS server settings

I tried that just now and it didn't work. Here is how my file looked after I modified it based on your suggestion:

Code:

default-lease-time 86400;
max-lease-time 86400;
option subnet-mask 255.255.255.0;
option broadcast-address 172.16.254.255;
option domain-name "localnet";

subnet 172.16.254.0 netmask 255.255.255.0 {
range 172.16.254.200 172.16.254.250;
option domain-name-servers 172.16.254.5, 172.16.254.1;
option routers 172.16.254.1;
}