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I have two ethernet interfaces, eth0, and eth1 on ubuntu 17.04. eth0 is configured for DHCP and obtains an IP address, gateway, and DNS servers. This is a mobile PC so these change everytime.

eth1 is a local network where I would like to provide a DHCP server with the basic features of supplying an IP (static or dynamic), gateway, search domain, and a primary and secondary DNS. I'd like to pass on eth0's DNS servers and not some static pre-known option. How is this accomplished?

Once I connect eth0, dnsmasq seems to be doing the resolving and I can't seem to find (a) where the two servers are stored and (b) dynamically instruct a DHCP server either isc-dhcp or dnsmasq or whatever to use those in the offers.

Much appreciated!

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I wonder if you need to pass DNS servers for the second interface, because I'm pretty sure that there is only one system resolver. But you can check your DNS-servers with:

$ nmcli connection show <CONNECTION_NAME> | egrep "DNS|\sdomain_name_servers"

You can list your active connection name with:

$ nmcli connection show --active

You can set new DNS-servers (8.8.8.8 and 8.8.4.4 in this case) with:

$ sudo dbus-send --system --print-reply --dest=org.freedesktop.NetworkManager.dnsmasq /uk/org/thekelleys/dnsmasq uk.org.thekelleys.SetDomainServers "array:string:8.8.8.8,8.8.4.4"

And check if it is succeed with:

$ journalctl -n -b _COMM=dnsmasq

and

$ sudo kill -USR1 `cat /var/run/NetworkManager/dnsmasq.pid` && sleep .5; journalctl -n -b _COMM=dnsmasq

Update: If you want to provide your own DHCP server which offer DNS records it's better to let your dnmasq instanse serve DNS queries. So let dnsmasq listen on your eth0 interface:

$ sudo tee <<< "interface=eth0" /etc/NetworkManager/dnsmasq.d/bind-eth0.conf
$ sudo systemctl reload NetworkManager

And set your DHCP server to offer eth0's IP address as the DNS-server.

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