DNS settings on Ubuntu 22.04 and FortiClient VPN 7.0.0.0018

[no_one]

I have a strange problem when I connect to a company VPN with forticlient application. First, I did not know what was wrong. After spending some time, I figured out that DNS is not working as it should have. Unfortunately, I have no idea, who's fault is that. It may be FortiClient VPN, systemd-resolved, or something else. I am using Ubuntu 22.04, which is not an official version yet, but I have doubts it will get any better until official release in a week or two.

This is output from resolvectl before VPN is established:

username@hostname:~$ resolvectl
Global
       Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: stub

Link 2 (enp2s0)
Current Scopes: none
     Protocols: -DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported

Link 3 (wlp1s0)
    Current Scopes: DNS
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 192.168.1.1
       DNS Servers: 192.168.1.1 2a00:ee0:d::13 2a00:ee0:e::13
        DNS Domain: --

After VPN is established resolvectl reports additional link called vpn:

username@hostname:~$ resolvectl
Global
       Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: stub

Link 2 (enp2s0)
Current Scopes: none
     Protocols: -DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported

Link 3 (wlp1s0)
    Current Scopes: DNS
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS 
DNSSEC=no/unsupported
Current DNS Server: 172.20.1.21
       DNS Servers: 172.20.1.16 172.20.1.21 2a00:ee0:d::13 2a00:ee0:e::13
        DNS Domain: company.com

Link 5 (vpn)
Current Scopes: none
     Protocols: -DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported

As you can see additional DNS servers are added to Link 3, which should help me resolve internal names when connected to VPN. Strange thing is that when I write

username@hostname:~$ resolvectl query name.company.com
name.company.com: resolve call failed: 'name.company.com' not found

I do not get anything. If I try with nslookup like this

username@hostname:~$ nslookup
> server 172.20.1.16
Default server: 172.20.1.16
Address: 171.20.1.16#53
> name.company.com
Server:     172.20.1.16
Address:    172.20.1.16#53

Name:   name.company.com
Address: 172.20.38.251

I get the correct answer. Since this was strange I traced network traffic to see what does nslookup differently than resolvectl query.

It turned out that nslookup uses a VPN assigned address for the source IP when asking DNS for a name. On the other hand, resolvectl query uses all other addresses for source IP except the one assigned by VPN. Because of that I guess DNS server does not have the route to send back an answer correctly to my computer, or DNS queries may even not reach the newly added DNS servers.

Because of that none of the programs I need can resolve the names correctly. The result is that I cannot connect anywhere within a VPN with a domain name.

Does anybody have an idea how to make resolvectl realize there is newly assigned VPN address, and it should use it as the source IP. Should FortiClient do some additional configutation on establishing a connection? Probably not.

I tried to restart systemd-resolved after VPN is established, but it does not help. Should I restart some other service? Which one?

I have checked how DNS is setup in network settings, and they are correct. Without VPN the network interface wlp1s0 shows:

username@hostname:~$ nmcli device show wlp1s0 | grep DNS
IP4.DNS[1]:                             192.168.1.1
IP6.DNS[1]:                             2a00:ee0:d::13
IP6.DNS[2]:                             2a00:ee0:e::13

After VPN is connected:

username@hostname:~$ nmcli device show wlp1s0 | grep DNS
IP4.DNS[1]:                             172.20.1.16
IP4.DNS[2]:                             172.20.1.21
username@hostname:~$ nmcli device show vpn | grep DNS
IP4.DNS[1]:                             172.20.1.16
IP4.DNS[2]:                             172.20.1.21

[Ghandalf-82]

Hi,

are there any news on this?

We are using FCT 7.0.9 with EMS license and also have this issue.

Also 7.2.1 is not solving this.

What I have found out: it is only not working when a IPv6 DNS server is used from the ISP.

I have created a ticket at Fortinet support, but as this issue is not solved for about a year now, I have not very much confidence, that it will be fixed soon...

Regarding this workaround from f_sfetea:

I have completely different interface names.

2: enp2s0f0 -> local laptop rj45 port

4: wlp3s0 -> WiFi

6: enx34298f721425 -> docking station rj45 port

11: vpn0090df7b1e -> FCT

It would be nice, when someone can clarify this.

BR

[danielmora]

This is my temporal workaround to set the DNS server.

I am using Ubuntu 22.04 and forticlient_vpn_7.0.7.0246_amd64.deb

1)Connect to the VPN using forticlient

2)Get the name of the VPN connection in your system by using:

$ resolvectl

In my case I get

"Link 20 (vpn000170bb2a)"

3)Use the vpn name connection to manually set the organization DNS (for example 10.10.10.10)

$sudo resolvectl dns vpn000170bb2a 10.10.10.10
$sudo resolvectl domain vpn000170bb2a ~.

4)To verify run again :

$resolvectl

Link 20 (vpn000170bb2a)
Current Scopes: DNS
Protocols: -DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 10.10.10.10
DNS Servers: 10.10.10.10
DNS Domain: ~.

This has to be executed every time you connect to the VPN. If anyone has a better and permanent solution please help.

[SlavaS]

Hi, tried this?

need to edit NM config:
sudo vi /etc/NetworkManager/NetworkManager.conf

and append the
[keyfile]
unmanaged-devices=interface-name:vpn*,except:interface-name:enp0s3;interface-name:wlan*

then restart your service
$ sudo systemctl restart NetworkManager.service

Another option:

Fix DNS on ubuntu and Forticlient VPN:
sudo vim /etc/systemd/resolved.conf

DNS=8.8.8.8 8.8.4.4
FallbackDNS=100.10.0.1  ### add your DNS here
##Domains
#DNSSEC=no
#DNSOverTLS=no
#MulticastDNS=no
#LLMNR=no
#Cache=no-negative
#CacheFromLocalhost=no
#DNSStubListener=yes
#DNSStubListenerExtra=
ReadEtcHosts=yes
#ResolveUnicastSingleLabel=no

systemctl restart systemd-resolved.service

[danielmora]

Thank you very much, FallbackDNS didnt work for me, I had to add the vpn dns as the first one in the list:

sudo vim /etc/systemd/resolved.conf

DNS=100.10.0.1 8.8.8.8 8.8.4.4
FallbackDNS=100.10.0.1
ReadEtcHosts=yes