The "3-layer rule" has multiple meanings depending on the context. It can refer to clothing layers for hiking or to network firewall rules.
1. The 3-Layer Clothing Technique for Hiking
This refers to a method of dressing for hiking to stay warm, dry, and comfortable in variable weather conditions. The three layers are designed to work together:
- Base Layer: A moisture-wicking layer (e.g., synthetic or merino wool t-shirt) that pulls sweat away from your skin.
- Mid Layer: An insulating layer (e.g., fleece or sweater) that traps heat and provides warmth.
- Outer Layer: A waterproof and windproof shell (e.g., rain jacket) that protects you from the elements.
This layering system allows you to adjust your clothing based on the intensity of your activity and the changing weather. As stated in Quechua's guide and Salomon's advice, this is a fundamental rule for hikers.
2. Layer 3 Firewall Rules in Networking
In networking, particularly with Cisco Meraki devices, the "3-layer rule" refers to Layer 3 firewall rules. As detailed in the Meraki documentation, these rules operate at the network layer (IP addresses and ports) to control network traffic. These rules are stateful, unlike Layer 7 rules, which are stateless, as noted in Meraki's documentation on processing order. Examples of Layer 3 rules include allowing or denying traffic based on source and destination IP addresses. This Meraki community post discusses using multiple CIDRs in a single rule.
