VPN ISIMA / LIMOS✯
We provide 2 .ovpn files - Which one to choose? 👇 CLICK HERE 👇
Overview✯
Our OpenVPN servers allow you to connect to ISIMA/LIMOS resources from outside the establishment. This service is intended for teacher-researchers, administrative staff, PhD students, and students.
The documentation has been validated for the following systems:
- Windows 10
- Debian 11/12
- Ubuntu 18.04, 20.04, 22.04
- Mac OS X Ventura
The OpenVPN service for students does not allow outgoing internet access. This is a decision by the ISIMA Management due to security incidents.
The setup is done in 3 steps:
Client installation✯
An up-to-date version of OpenVPN is recommended. We advise you to update your client if you experience connection issues. As of today, the latest client version is 2.6.6
Do not download OpenVPN Connect, which is not the same product
Retrieving OpenVPN configuration files✯
Log in to https://my.isima.fr/ovpn with your account and download the .ovpn files:
You can download all .ovpn files you are authorized to access by taking the ZIP. Alternatively, you can simply download the specific file you need.
You will find 2 versions of this OVPN file. One uses a TCP connection, the other UDP. It is advisable to have both installed on your machine to choose which one to use based on what you plan to do on the network or the conditions under which you connect to the internet.
If you experience issues with one file, start by testing the other. Please verify that you have the latest version of your OpenVPN client.
TCP or UDP - How to choose?
Too long; didn’t read:
| TCP | UDP | |
|---|---|---|
| My connection is stable (high-quality home connection, good Wi-Fi or wired) | X | |
| I am connected to a low-speed or unstable network (phone hotspot, poor Wi-Fi reception, old internet setup) | X | |
| I am in a hotel, airport, train station, or on public Wi-Fi | X |
For more precise guidance:
TCP✯
Advantages✯
- High reliability: TCP’s error control ensures successful downloads and prevents connection interruptions.
- High compatibility: Most networks and firewalls work well with it, ensuring broad compatibility, even in highly controlled networks.
Disadvantages✯
- Lower speed: TCP’s error correction mechanism comes at the cost of speed. For each packet sent, the sender must receive an acknowledgment from the recipient before sending more data. This creates overhead and significant delays in a VPN connection.
- Latency/Lag: If your internet connection is somewhat unstable, delays may occur. For most static data (websites, file downloads, etc.), this delay is both acceptable and preferable. However, for time-sensitive applications like VoIP, video streaming, or audio streaming, it is better to use the VPN in UDP mode.
UDP✯
Advantages✯
- Handling slow connections: In some cases, the overhead from VPN encryption can result in very poor connection performance. Using UDP instead of TCP can speed things up by reducing additional processing and error correction delays.
- Transmitting time-sensitive data: If you send or receive VoIP traffic (phone calls) or live video (videoconferencing) via your VPN connection, UDP is the preferred choice. The same applies to video and audio streaming. In all these cases, the UDP protocol is perfectly suited.
Disadvantages✯
- Less reliability: Sending information using UDP carries the risk of missing or corrupted data when network conditions are not ideal. This can lead to download failures or connection interruptions as errors accumulate to an unmanageable level.
- Compatibility issues: In some network environments, incoming and outgoing traffic is restricted to maintain network security. The UDP protocol is generally more restricted than TCP. Using it in such environments may result in OpenVPN connection failures (hotels, public Wi-Fi, etc.).