[RESOLVED]No internet on ubuntu when disable dhcp

Farisse · Jul 10, 2020, 5:42 PM

@kiokoman Thank you i will take a look at the post :)

Farisse · Jul 11, 2020, 1:26 PM

Update !

So i reinstalled my ubuntu machine and deactivated netplan and ... It didn't work.

The simple reason is, i am working on a private network they have their own DNS servers.

So when i am using the DHCP server there is apparently an automatic DNS forwarding to my machine. The DNS of my school but its hidden in the ubuntu settings. (ofc)

So now when i tried to put the dns of my school in my /etc/systemd/resolved.conf document. It worked.

Now i'm wondering if you may help me to understand how i could make it work without adding the dns of my school in the /resolved.conf ?

I thought about dns forwarding, but not sure about the working.

If someone can help it would be great. If not, moderator can close the subject and mark it as solved.

Thank you for your help ! :)

Farisse

bmeeks · Jul 11, 2020, 1:28 PM

@Farisse said in No internet on ubuntu when disable dhcp:

Update !

So i reinstalled my ubuntu machine and deactivated netplan and ... It didn't work.

The simple reason is, i am working on a private network they have their own DNS servers.

So when i am using the DHCP server there is apparently an automatic DNS forwarding to my machine. The DNS of my school but its hidden in the ubuntu settings. (ofc)

So now when i tried to put the dns of my school in my /etc/systemd/resolved.conf document. It worked.

Now i'm wondering if you may help me to understand how i could make it work without adding the dns of my school in the /resolved.conf ?

I thought about dns forwarding, but not sure about the working.

If someone can help it would be great. If not, moderator can close the subject and mark it as solved.

Thank you for your help ! :)

Farisse

It is a fairly common practice for schools to intercept DNS requests and redirect/force them to a school-maintained DNS server. The school's DHCP server is giving all machines on the network the proper DNS server to use. This is done to monitor for and/or prevent access to inappropriate content. It also allows the school to have DNS entries they maintain for local servers and services. If your school network is doing this, then you won't be able to use another DNS server unless you perhaps can get something running over a VPN.

Farisse · Jul 11, 2020, 3:06 PM

@bmeeks
Thank you for your answer
Indeed, i have to use the dns of the school. But what i don't understand is, i don't put anything on my windows machine except the static ip, gateway that's all and it works. But on my ubuntu machine it doesn't work. So i don't understand how it works in pfsense to let my windows machine use the dns i entered in pfsense and not my ubuntu machine. It's not logic for me :/

bmeeks · Jul 11, 2020, 3:19 PM

@Farisse said in No internet on ubuntu when disable dhcp:

@bmeeks
Thank you for your answer
Indeed, i have to use the dns of the school. But what i don't understand is, i don't put anything on my windows machine except the static ip, gateway that's all and it works. But on my ubuntu machine it doesn't work. So i don't understand how it works in pfsense to let my windows machine use the dns i entered in pfsense and not my ubuntu machine. It's not logic for me :/

Is your Windows machine a member of an AD domain? If so, the AD domain controller is the DNS server, and it probably forwards to the school's DNS server (or it may actually be the school's DNS server).

Farisse · Jul 11, 2020, 4:00 PM

@bmeeks Nope its not :(
I just tried but my windows machine is not member of AD domain.
here is a little video : https://streamable.com/6mznjo
even with the schools dns it doesn't work anymore. Really strange things are happening here :/

bmeeks · Jul 11, 2020, 4:04 PM

@Farisse said in No internet on ubuntu when disable dhcp:

@bmeeks Nope its not :(
I just tried but my windows machine is not member of AD domain.
here is a little video : https://streamable.com/6mznjo
even with the schools dns it doesn't work anymore. Really strange things are happening here :/

I am not a user of Hyper-V. I am an ESXi user. One place I would concentrate my research is within the networking configuration of Hyper-V.

Are you running Hyper-V on hardware by itself, or are you running Hyper-V on say a Windows desktop? There will be substantial changes to some of the networking in one installation versus the other.

Farisse · Jul 11, 2020, 4:14 PM

@bmeeks
I don't think the problem should come from the hyper v configuration. I think this because all the other machines are working, and its only ubuntu machines that doesn't work. (Maybe i should go to an ubuntu forum sorry for that). I work on a windows desktop.
So i have a VPN connection to the windows machine where is installed windows server and hyper-v manager.
I think the problem should be something like resolving he dns between the ubuntu machine and pfsense but idk where to search :/

Farisse · Jul 11, 2020, 11:38 PM

After a lot of research i'm asking myself if someone could maybe tell me where i could find any information about the changes that are made when the dhcp server is enabled.

I searched in the pfsense book, but it is not written how it works. If i find what changes are made i would be able to find where the problem is with my server.

Thank you guys !

johnpoz · Jul 12, 2020, 12:27 AM

And again - The dhcp server being on or off has ZERO to do with whatever issue your having.

The only changes that happen that you might not see when you enable a dhcp server on a specific interface, is some hidden rules get added to allow for dhcp to reach the server running on pfsense..

bmeeks · Jul 12, 2020, 1:21 AM

Okay, going back and reading your original post one more time, this is what I am hearing you say:

When you turn on or enable the DHCP server in pfSense and you enable DHCP in your Ubuntu machine, you have Internet access. But when you turn off the DHCP server in pfSense and try a static IP with no DHCP configured in Ubuntu, you have no Internet access.

If the above is correct, then this is what I think is happening. You are never actually disabling the DHCP client on the Ubuntu machine even though you might think you are. So when you turn off the DHCP server in pfSense, the DHCP client on Ubuntu can't get a proper IP address and thus you have no connectivity. With the DHCP server running on pfSense, the Ubuntu DHCP client can get the info it needs and the Internet works on the Ubuntu machine.

That's what I believe is happening. You think you are turning off DHCP on the Ubuntu machine and switching to a static IP, but I'm thinking perhaps you are not actually doing that. I know that it can be a real pain to re-plumb the network in modern Linux distros with their fancy GUIs. They really, really want to use the DHCP client.

Farisse · Jul 12, 2020, 12:05 PM

@johnpoz You are right, but where could i find these rules ? My firewall rules are empty (or everything is open). There is something i am missing in this configuration. It makes me sick of not understanding why sometimes it works and sometimes not with the same configuration.

@bmeeks i actually don't even know when it's working or not. I had a few minutes ago an internet connection on my machine and, a few minutes later nothing anymore.

How could i get more details about this ? Logs ?

johnpoz · Jul 12, 2020, 12:30 PM

@Farisse said in No internet on ubuntu when disable dhcp:

My firewall rules are empty (or everything is open)

If your firewall rules are EMPTY then everything is blocked!

Farisse · Jul 12, 2020, 12:46 PM

@johnpoz No sorry I mean everything is open

johnpoz · Jul 12, 2020, 1:02 PM

And clearly you have 13 states currently open using that rule, and have moved 63.18 MB of traffic.

How about some actual info... Lets see you ping the DMZ address from this client.. Lets see you do a dns query to what the dmz address, some other dns server?

Lets see the ifconfig output from this client. When you say it doesn't work, and then when you say it works if you turn on dhcp on pfsense.

Farisse · Jul 12, 2020, 1:02 PM

@johnpoz said in No internet on ubuntu when disable dhcp:

How about some actual info... Lets see you ping the DMZ address from this client.. Lets see you do a dns query to what the dmz address, some other dns server?
Lets see the ifconfig output from this client. When you say it doesn't work, and then when you say it works if you turn on dhcp on pfsense.

i am not sure about understanding the questions do you mean that i show the results of the commands you said ?

There are 2 dns servers. One one the schools network and the other in my lan network.

johnpoz · Jul 12, 2020, 1:09 PM

Yes lets see the output of the commands.. Not just you saying something doesn't work via what a browser? ping pfsense dmz address, if you can't then your never getting anywhere.. If you can not query dns then your never going to get anywhere via fqdn.

Lets see say a traceroute when it works, and when it doesn't work to both an IP say 8.8.8.8 and then say via a fqdn like www.google.com

Your not doing something like static arps are you in pfsense?

If you setup a static arp say for 1.2.3.4 mac xyz so that what the client gets when dhcp is on, and then you setup IP on the machine to be 1.2.3.5 then no it wouldn't work.

Farisse · Jul 12, 2020, 1:30 PM

@johnpoz
the video is uploading i'll add screenshots in a few minutes
https://streamable.com/j30bzs

Ping from Windows Hyper-v to DMZ network

Ping from Ubuntu to DNS/DMZ network + ifconfig

Do you need more info ?

johnpoz · Jul 12, 2020, 2:05 PM

And that is with dhcp or static? And where is your dns query?

Farisse · Jul 12, 2020, 2:17 PM

This is Static the video is when internet was functional and then after reboot ... nothing anymore

here is the dns query: