FortiClient VPN bytes received 0

[francescobalatti]

Hi, I'm using FortiClient VPN for conneticting to a customer's VPN but I can't receive any bytes:

Same username and password on other PC work and every username and password on my PC don't work.

I tried disabling/closing: firewall, antivirus, teams, onedrive, ...

I have the default settings of Windows 11 and I'm using FortiClient 7.0.7.0345.

VPN configuration is correct.

Could someone help me please?

Thanks in advance

Francesco

MAS Consulting

[luizf29]

I had the msm problem and I managed to download a version of forticlient_vpn_7.0.7.0246_amd64.deb from this website, https://aur.archlinux.org/packages/forticlient-vpn, I solved my problem and now I can finally use a vpn

[mlarramendi]

Hello, I was recently having the same problem, but we realized that we had a conflict between the IPsec subnet range and the DMZ interface, maybe the problem is because some interface is in conflict with the IPSec subnet.

[ps-support]

Experienced the same issue this morning.
FortiClient: 7.0.7.0345
Windows 11

What worked for me was disabling IPv6 on the FortiClient SSL VPN virtual network adapter. 

[Tahsin]

Hi francescobalatti,

Do you use any endpoint protection application like symantec,mcafee?

[Cyn0wn]

Hi everyone,

This is my first post in this community, and I’d like to share a solution that worked for us. I found the root of the problem and have a few tips that might help others.

First of all, it's important to note that this is purely an IPv6-related issue.
When connecting via IPv4, there were no problems at all with any version of FortiClient.
Also, we did not have an EMS server at the time of testing.

Version	IPv4	IPv6
FortiClient 7.0 - 7.2.1.0779	yes	yes
7.2.2 - 7.2.9	yes	no (connection established but 0byte received) After a few seconds connection drop because of Dead-Peer-Detection
7.2.10	yes	yes
7.4.0 - 7.4.3	yes	no (connection established but 0byte received) After a few seconds connection drop because of Dead-Peer-Detection

Other versions were not tested because, as is often the case, admins tend to do only as much as needed to make things work.

After purchasing an EMS server, we noticed the following setting:

Here's what we did:

• Configured the EMS server

• Created the invitation

• Set up endpoint profiles (including VPN tunnels and other settings)

• Created the installation package

• Disabled the “Block IPv6” setting under Remote Access

• Deployed FortiClient version 7.4.3 (latest at the time) to users

Result: IPv6 connections began working normally again.

Out of curiosity, we re-enabled “Block IPv6” — and the issue immediately returned: 0 bytes received, just like in every version after 7.2.2.
We could hardly believe that this small checkbox was the root cause of such a frustrating issue.

Our theory:
This behavior is likely intentional. Most companies use EMS and can easily disable this setting. However, when upgrading FortiClient without EMS, you're stuck with this “feature” enabled by default — and there’s no obvious way to know that it even exists.

Prerequisites to Avoid This Issue:

1. Avoid the following Windows Updates:

   • KB2693643

   • KB5026372

2. Install Microsoft Visual C++ 2015–2022 Redistributable

   • Microsoft Download 
3. Use an EMS server to disable “Block IPv6” if upgrading to FortiClient versions above 7.2.2

I hope this helps someone out there — especially since, at the time of writing, nobody seems to be talking about this checkbox. Not on Google, Reddit, or any forums.

That’s why I wanted to share it with you.