Public bug reported:

On freshly installed and fully updated Ubuntu 24.04.2 there is a
regression that prevents VPN connections to Meraki MX firewalls using
with the following configuration (which worked perfectly in Ubuntu 22.04
and prior releases):

https://community.meraki.com/t5/Security-SD-WAN/Guide-Client-VPN-on-
Linux-Debian/m-p/72315

This is the permanent error from the logs:

level=debug tunnel_name=t1 function=transport message=recv 
message_type=avpMsgTypeSli
level=error tunnel_name=t1 message="bad control message" 
message_type=avpMsgTypeSli error="no specification for v2 message avpMsgTypeSli"

The connection process shows:

1. The IPsec tunnel establishes successfully
2. The L2TP tunnel starts to establish
3. Then there's a failure when receiving a "Set Link Info" (SLI) message from 
the Meraki server

The local L2TP client doesn't understand this message type and
disconnects

This appears to be a compatibility issue between the L2TP implementation
in fresh Ubuntu 24.04.2 and the Meraki MX firewall. Interestingly, this
same issue does not occur on fresh Debian 12 installs or on systems
upgraded from previous versions.

The L2TP protocol implementation may have changed in Ubuntu 24.04.2

There might be a version mismatch between packages in fresh vs. upgraded
installations.

Some configuration file or setting that handles these message types
properly might be preserved during upgrades but not set correctly in
fresh installations

Since fresh Debian 12 installations are now working, this narrows down
the issue specifically to Ubuntu 24.04.2 fresh installations, which
should help in identifying and resolving the regression.

Workaround:

sudo add-apt-repository ppa:nm-l2tp/network-manager-l2tp && sudo apt
update && sudo apt install network-manager-l2tp network-manager-l2tp-
gnome go-l2tp && sudo systemctl restart NetworkManager

After adding the repository above and replacing the packages from Ubunu
24.04.2 with the ones from this repository (and restarting
NetworkManager. The created VPN profile immediately begins to work as
expected.

This work-around was provided by Douglas Kosovic during this bug report:
https://github.com/nm-l2tp/NetworkManager-l2tp/issues/237

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: network-manager-l2tp-gnome 1.20.12-1build2
ProcVersionSignature: Ubuntu 6.11.0-21.21~24.04.1-generic 6.11.11
Uname: Linux 6.11.0-21-generic x86_64
ApportVersion: 2.28.1-0ubuntu3.5
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Sat Apr 12 22:39:02 2025
InstallationDate: Installed on 2025-04-13 (0 days ago)
InstallationMedia: Ubuntu 24.04.2 LTS "Noble Numbat" - Release amd64 (20250215)
ProcEnviron:
 LANG=en_US.UTF-8
 PATH=(custom, no user)
 SHELL=/bin/bash
 TERM=xterm-256color
 XDG_RUNTIME_DIR=<set>
SourcePackage: network-manager-l2tp
UpgradeStatus: No upgrade log present (probably fresh install)

** Affects: network-manager-l2tp (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug noble wayland-session

** Attachment added: "vpn-debug.log"
   
https://bugs.launchpad.net/bugs/2107270/+attachment/5871463/+files/vpn-debug.log

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https://bugs.launchpad.net/bugs/2107270

Title:
  Regression Preventing VPN to Meraki MX

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