Firewall

A firewall is a security control that inspects network traffic and permits or denies it according to a rule set. Rules typically match source and destination IP, port and protocol, and stateful firewalls also track whether a packet belongs to an established connection.

Why it matters

A firewall reduces the attack surface by exposing only the services you intend, such as ports 80 and 443 on a web server, and by hiding everything else. Cloud providers call them security groups. A firewall is also a common cause of unexplained connection timeouts when a rule silently drops traffic.

Example

# ufw on a Linux web server
ufw default deny incoming
ufw allow 22/tcp
ufw allow 443/tcp
ufw enable

Only SSH and HTTPS are reachable. A port check against port 3306 would now time out rather than get a refusal.

Common mistakes

• Locking yourself out by enabling a deny-all policy before allowing SSH.
• Opening a database port to 0.0.0.0/0 for convenience.
• Confusing a network firewall with a web application firewall, which inspects HTTP requests.

Related

• WAF
• Port
• NAT
• DMZ
• टूल: Port checker

यह पेज सामान्य जानकारी है, जिसे हमारी संपादकीय टीम ने लिखा है और दस्तावेज़ीकरण बदलने पर अपडेट किया जाता है। सर्वर और प्रदाता अलग-अलग होते हैं, इसलिए बदलाव पहले सुरक्षित तरीके से जाँचें। देखें: संपादकीय नीति और अस्वीकरण.