Module 15
Firewalls and ACLs
Deciding what gets through. Write rules, send packets at them, and learn why the order of an access list changes everything.
Start lesson 1
Which rule decides this packet? · 7 min · free, no account
TransportOpen now
What you'll operate
- Stateless and stateful filtering
- Why rule order matters
- Reading an access list
- lessons
- 6
- minutes
- 51
Lessons in this module
- 1Which rule decides this packet?See how a firewall reads its list of rules: from the top, stopping at the first match, with a deny at the end that nobody typed.Free, no account7 min
- 2Why does rule order change everything?See a broad permit swallow a specific deny, then put rules in the order that makes them work.Plus8 min
- 3Why did the reply get blocked?Watch a stateless filter drop the answer to a packet it let out, and weigh the ways to fix that.Plus9 min
- 4How does a firewall remember a connection?Play a handshake through a stateful firewall, read its connection table, and see what it drops that a stateless filter lets in.Plus9 min
- 5Where should the filter go?Split a network into zones, give public servers a zone of their own, and learn what no firewall placement can see.Plus9 min
- 6Is the firewall why it broke?Recognize the faults firewalls cause: a reply on another path, one blocked ICMP message, and silence where an error should be.Plus9 min
Lesson 1 is open to everyone, with no account. The other lessons in this module are part of Plus.