Layer3Switches

Layer3 switches are network devices that combine switching and routing functions in a single device. Unlike traditional layer 2 switches, which forward frames within VLANs, Layer3 switches can route packets between VLANs and other networks, enabling inter-VLAN communication at high speed. They are commonly used in enterprise networks to provide fast, scalable inter-VLAN routing and to serve as edge devices that connect LAN segments to external networks.

Key capabilities include IP routing, switching between VLANs via SVIs (switched virtual interfaces), and support for static routes as well as dynamic routing protocols such as OSPF, EIGRP, RIP, and BGP on many platforms. Layer3 switches typically handle VLAN creation, trunking, port channels, and quality of service. They also offer features such as access control lists, multicast filtering, IPv6 support, and sometimes virtual routing and forwarding (VRF) for route isolation. Many devices implement routing in hardware (ASICs) for fast forwarding, while the control plane runs an operating system that manages policies and routing tables.

Deployment considerations: Layer3 switches are well suited for campus networks and data centers that require fast inter-VLAN routing and simplified network design. They can replace separate routers for internal routing or function as edge devices toward WAN links. However, they may not offer the same breadth of advanced features or scalability for large-scale external routing as dedicated routers, depending on the model and vendor.

Configuration basics typically include creating VLANs, assigning access ports, configuring SVI interfaces with IP addresses, enabling IP routing, and configuring static routes or dynamic routing protocols. Many devices also provide VRFs, ACLs, QoS, and multicast controls, with management through CLI, web UI, or APIs.