Core Switch Subnet Configuration Scheme

Core switch subnet configuration involves creating VLANs, assigning IP addresses, enabling DHCP relay, and configuring Layer 3 routing for inter-VLAN and upstream connectivity.

VLAN and Subnet Setup

Create VLA

Ns: Define VLANs for each subnet on the core switch. For example, VLAN 10 for R&D wired users and VLAN 20 for management. Assign a descriptive name to each VLAN for easier management.

Assign I

P Addresses: Configure a VLAN interface (SVI) for each VLAN with a static IP address. Example: VLAN 10: 10. 1.

10. 1/24VLAN 20: 10. 1.

20. 1/24 This IP serves as the default gateway for devices in that VLAN.

Enable DHC

P Relay: If DHCP servers are centralized, enable DHCP relay on the VLAN interfaces and specify the DHCP server IP. This allows clients in each VLAN to obtain IP addresses automatically. Layer 3 Routing Between Core and Distribution SwitchesRouted Ports or SVIs: Configure the uplink between the core and distribution switches as a routed port or use a /30 subnet for point-to-point connectivity.

Both ends must be in the same subnet. Example: Core: 10. 10.

10. 2/30Distribution: 10. 10.

10. 1/30. Routing Protocols: Advertise VLAN subnets to the core switch using static routes or a dynamic routing protocol like OSPF.

For multiple VLANs, configure OSPF on both core and distribution switches and mark VLANs as passive if needed. Inter-VLAN Routing: Enable routing on the core switch to allow communication between VLANs.

Each VLAN SV

I acts as a Layer 3 interface for routing traffic.

Connectivity to Firewalls and External Networks

Create Interconnection VLA

Ns: Configure VLANs for links to firewalls or BRAS devices.

Assign VLANI

F interfaces and bind them to a VPN instance if route isolation is required. Static or Default Routes: Configure static routes or default routes pointing to the firewall or upstream router to ensure traffic from user VLANs reaches external networks.

OSP

F Configuration: If using OSPF, include VLAN interfaces and interconnection links in the OSPF process to propagate routes dynamically.

Best Practices

Use descriptive VLAN and interface names for easier management. Keep point-to-point links between core and distribution switches in /30 subnets to conserve IP addresses.

Enable DHC

P relay only on VLANs that require centralized DHCP. Verify routing with commands like show ip route and OSPF neighbor status.

Consider VP

N instances or VRFs to isolate traffic between public and private networks. By following these steps, the core switch will provide Layer 3 connectivity, DHCP services, and inter-VLAN routing, ensuring efficient communication across the campus network.