Core Switch VLANs

VLANs should generally be configured on the core switch, especially if it is Layer 3 capable, to enable efficient inter-VLAN routing and centralized management.Core Switch Role and VLAN PlacementA core switch serves as the high-capacity backbone of a network, aggregating traffic from distribution and access switches and routing data between VLANs and external networks . Whether VLANs need to be configured on the core switch depends on the switch type and network design:Layer 2 Core Switch: VLANs must be defined on the core switch if it participates in VLAN trunking between access/distribution switches. The core acts as a pass-through for VLAN traffic, so all VLANs that traverse the core need to exist there .Layer 3 Core Switch: VLANs are typically configured with SVI (Switch Virtual Interfaces) to enable inter-VLAN routing at line speed. Only VLANs that require routing or act as gateways need SVIs; other VLANs may exist only on access/distribution switches .Configuration ConsiderationsTrunking: If multiple switches share VLANs, configure trunk ports on the core switch to carry all relevant VLANs between switches .Routing: For Layer 3 cores, create SVI interfaces for each routed VLAN and assign IP addresses to serve as the default gateway for devices in that VLAN .Security and Segmentation: VLANs on the core switch allow centralized enforcement of ACLs and routing policies. High-security VLANs may still route through a firewall for stateful inspection .Management: Best practice is to manage VLANs from a single location (usually the core switch) to avoid configuration inconsistencies .Practical ExampleVoice VLANs: If deploying a new voice VLAN, it should be configured on the core switch if the core is Layer 2 or Layer 3 and participates in trunking or routing for that VLAN .Interconnection VLANs: VLANs connecting the core to firewalls, BRAS, or other network devices should be created on the core switch and associated with the appropriate interfaces or VPN instances .SummaryAlways define VLANs where they are used: access/distribution switches for end devices, core switch for aggregation and routing.Layer 3 cores: configure SVIs for VLANs that require routing.Layer 2 cores: configure VLANs for trunking and pass-through.Centralized management: maintain VLANs primarily on the core switch to simplify administration and ensure consistent network behavior .