Implicit or Explicit, Allow or Deny?

About this interactive

Access control lists behave differently depending on where they are used, and the Access Control lesson uses a firewall to show implicit and explicit behavior. Implicit means nobody had to write it down: it is what the firewall does by default. Explicit means an administrator wrote a rule for it. The lesson's firewall treats the inside of the network as trusted and the internet as untrusted. From the inside out there is an implicit allow, so a laptop can browse with no rule written for it, and blocking something takes an explicit deny. From the outside in there is an implicit deny, so nothing gets in unless an explicit allow lets it. Rules are read from the top, and the first one that matches decides, so an explicit allow placed above a block can make an exception (and the other way round). Not every device has these defaults. Many router access lists, and many firewalls, end with an implicit deny for each direction, so outbound traffic needs explicit allows too. Always check how the device in front of you behaves. The cards here use the lesson's firewall, as the subtitle says. A quick test for each card: did someone write a rule for this traffic? If not, which way is it going?

What you'll learn

Decide what a firewall does with traffic and why: an implicit allow or deny from its default behavior, or an explicit allow or deny from a rule an administrator wrote
Apply the lesson's firewall defaults: from the trusted inside out is implicitly allowed, from the untrusted outside in is implicitly denied, and explicit rules make the exceptions

Aligned to

CompTIA Security+

4.5 Given a scenario, modify enterprise capabilities to enhance security.

NIST 800-53

AC-3 Access Enforcement

Key terms

Explicit Allow: An ACL rule that specifically and intentionally permits a defined type of traffic or access to a resource.
Explicit Rule: An access control rule that is directly stated and deliberately configured by an administrator.
Implicit Rule: An access control rule that is not directly stated but is automatically applied by default, such as a deny at the end of an ACL.
Access Control List: A set of rules that defines which users or systems are granted or denied access to a resource.
Access Control: A security mechanism that restricts access to resources based on policies, roles, or identity.

Topics

Access Control Firewall Interactive Categorize

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