It is also known as the Top-of-Rack (ToR) switch. A three-tier architecture is illustrated as follows. This document provides design guidance for implementing a routed (Layer 3 switched) access layer using EIGRP or OSPF as the campus routing protocol. What's a Layer 1 (L1) Switch? Let's be real—“L1 switch” is kind of a misnomer. It works in our network by simply allowing connected devices that are on the same subnet or virtual LAN (VLAN) to exchange information at lightning speed, just like a switch. Aggregation Layer: This layer connects to the access switches and also provides other services (FW, SLB, etc.