Can perimeter firewalls prevent attacks on internal networks?

Perimeter firewalls can help prevent attacks on internal networks to a certain extent, but they are not foolproof.

A perimeter firewall acts as a barrier between an organization's internal network and external networks (like the internet). It monitors and controls incoming and outgoing traffic based on predefined security rules. By blocking unauthorized access, malicious traffic, and known attack patterns, perimeter firewalls reduce the risk of external threats reaching internal systems.

Example:
If an attacker tries to scan your internal network ports from the internet, a perimeter firewall can block those attempts if they violate the configured rules. Similarly, it can prevent malware-infected downloads or phishing-related connections from reaching internal users.

However, perimeter firewalls have limitations:

1. Internal Threats: They cannot protect against attacks originating from within the internal network (e.g., a compromised employee device or insider threats).
2. Advanced Attacks: Sophisticated attacks like zero-day exploits or lateral movement by attackers who bypass the firewall may still reach internal systems.
3. Encrypted Traffic: If encrypted traffic (HTTPS) is not inspected, threats hidden inside can pass through undetected.

To enhance protection, organizations should combine perimeter firewalls with additional security measures such as intrusion detection/prevention systems (IDS/IPS), endpoint security, network segmentation, and internal firewalls.

For cloud environments, Tencent Cloud provides solutions like the Tencent Cloud Firewall (CFW) and Virtual Private Cloud (VPC) with security groups and network ACLs to help secure both perimeter and internal traffic. These services allow fine-grained control over traffic flow and threat prevention.