Skip to content
AI Security

Interview question · Network Security & Protocols

How do firewalls work underneath: stateless vs stateful filtering, connection tracking, the netfilter path, and failing rule sets?

A firewall is a list of match conditions evaluated in order against fields it can see, plus a table that remembers connections. Almost every firewall failure is in one of those three words: order, fields, remember.

mediumEssentialNewPreparation tags: Palo Alto Networks, Check Point, CiscoUpdated Nov 2026

A firewall is a list of match conditions evaluated in order against fields it can see, plus a table that remembers connections. Almost every firewall failure is in one of those three words: order, fields, remember.

Make your first attempt

What would you say before reading the answer?

  1. 01 State the assumptions your answer depends on.
  2. 02 Explain the mechanism and choose a control.
  3. 03 Name a condition that would change your decision.

The worked answer includes an approach, scoring criteria and follow-up questions. Compare the reasoning with your own.

10 answers per topic instead of 5, plus saved progress and bookmarks · costs nothingor unlock all 529 remaining answers · $25

Every worked answer in all 17 topics, every lesson in every course, the full concept curriculum, the complete practice-test bank, and the downloadable security field guides.

6 months · One payment · No auto-renewal

What if · the follow-ups in this answer

The answer works through 6 follow-ups like an interviewer would

You inherit a perimeter firewall with a rule set nobody fully understands, protecting a web application and an internal network.

  1. How do stateless and stateful firewalls differ?
  2. Why is 'allow established' usually first?
  3. How would you review the unknown rule set?
  4. What should the target policy be?
  5. How do you change it safely?
  6. How would you take ownership of the firewall?

Each rung has a nudge, a model answer, the principle that carries over and the weak answer to avoid. Premium opens every answer and ladder.

UP NEXT ON YOUR JOURNEY
Next in this trackForward proxies, reverse proxies and WAFs: how each works, which headers you can trust behind them, and how WAFs get bypassed.Next in this trackHow do ARP spoofing, MAC flooding, VLAN hopping and rogue DHCP work on a local network, and which switch and protocol controls stop them?Next in this trackHow does IPsec work: IKEv2 negotiation, security associations, ESP versus AH, tunnel versus transport mode, and NAT traversal?
DISCUSSION · 0

No comments yet. Share a correction or a different way to answer it.