The core idea: encryption isn’t the same as control
A VPN and a firewall solve different problems in the same “security pipeline.” A VPN mainly protects data as it travels by creating an encrypted tunnel between your device and the VPN endpoint. A firewall controls connectivity—deciding which incoming and outgoing connections are allowed, blocked, or restricted based on rules.
Even if your traffic is encrypted inside the VPN tunnel, you can still have risks if the wrong kinds of connections are allowed on your device, on your router, or on the network segment where the VPN terminates. In other words: encryption helps protect the contents of traffic; a firewall helps manage which traffic is permitted.
A simple model: what happens without firewall rules
Imagine your device is connected to a network where you can reach services (or where services can be reached). Without appropriate firewall filtering, there may be unnecessary exposure—open ports, permissive inbound rules, or services that accept connections you didn’t intend to allow.
A VPN doesn’t automatically “fix” these conditions. If your firewall posture is too open, an attacker may still attempt to reach reachable services. A firewall can reduce the reachable surface by blocking unsolicited inbound connections and constraining outbound access where it makes sense.
Where firewalling matters most in a VPN setup
- Inbound access to your device or LAN: Firewalls can block unsolicited incoming connections from the wider network, even when your VPN is active.
- Outbound control from your device: Some environments benefit from limiting which destinations and ports the device can reach, reducing the chance that malware communicates with unexpected endpoints.
- Segmenting trust at the VPN boundary: When a VPN connects remote devices to a local network, the firewall can enforce “only what you need” between those zones.
- Fail-safe behavior during VPN disconnects: Without firewall restrictions, a VPN disconnect or route change may leave connectivity gaps or unexpected paths. Well-chosen firewall rules can prevent accidental exposure.
Because VPN behavior can vary by setup, it’s worth treating this as a general principle rather than a guarantee for every configuration.
Differences and limits: when you might feel the firewall is “less important”
A firewall may feel optional if your environment is already tightly locked down—e.g., default-deny inbound rules, no exposed services, and conservative outbound restrictions. In that case, the practical risk reduction from additional firewall tuning may be smaller.
Also, a firewall is not a substitute for correct VPN configuration, strong authentication, and safe device practices. And a VPN is not a substitute for firewall rules: encryption alone doesn’t ensure that unwanted traffic won’t be allowed by your network policies.
Finally, some VPN implementations handle routing and traffic selection differently, so exact behavior depends on your platform and configuration. Treat “VPN + firewall” as complementary components, not a single combined feature.
Practical use: how to check your own setup
You can validate the idea with a few checks:
- Verify inbound policy: Make sure unsolicited inbound connections to your device or network are blocked unless you explicitly need them.
- Review allowed ports/services: Confirm you only permit the services required for your use case.
- Check behavior during changes: Consider what happens when the VPN connects, disconnects, or reconnects—ensure firewall rules still prevent unwanted exposure.
- Confirm traffic direction intent: If you need remote access to a service, allow that explicitly; otherwise keep inbound and lateral movement constrained.
If you share what kind of VPN setup you have (remote-access VPN to a device, or site-to-site into a LAN) and which platform/router you use, you can reason more precisely about which firewall rules are most relevant—without relying on assumptions.