ACL (Access Control List) in Networking
An ACL is a rule list that permits/denies traffic based on matching criteria.
Updated: 2026-03-05
Definition
Networking ACLs are ordered rules applied to interfaces to filter traffic by IP, protocol, and ports.
They are commonly used for basic traffic control, segmentation, and restricting management access.
Key points
- Order matters (first match wins)
- Implicit deny at the end in many systems
- Can be standard (source-only) or extended (more fields)
Common mistakes
- Forgetting rule order and locking yourself out of management access.
- Not documenting intent and creating overlapping rules.
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