How to configure the core switch for three networks

To configure a core switch for three networks, you need to create VLANs for each network, assign IP addresses to VLAN interfaces, configure inter-VLAN routing, and connect access switches or routers appropriately.

Step 1: Plan VLANs and IP Subnets

• Assign a unique VLAN ID for each network (e.g., VLAN 10, VLAN 20, VLAN 30).
• Allocate an IP subnet for each VLAN (e.g., 192.168.10.0/24, 192.168.20.0/24, 192.168.30.0/24).
• Decide on a management VLAN separate from user VLANs (e.g., VLAN 5) and assign a management IP address for switch administration .

Step 2: Configure VLANs on the Core Switch

• Enter global configuration mode: configure terminal
• Create VLANs:

  vlan 10name NetworkAexitvlan 20name NetworkBexitvlan 30name NetworkCexit

• Assign ports to VLANs as access ports for connected devices:

  interface GigabitEthernet0/1switchport mode accessswitchport access vlan 10exitinterface GigabitEthernet0/2switchport mode accessswitchport access vlan 20exitinterface GigabitEthernet0/3switchport mode accessswitchport access vlan 30exit

Step 3: Configure VLAN Interfaces for Routing

• Enable Layer 3 routing on the switch if supported:

  interface vlan 10ip address 192.168.10.1 255.255.255.0no shutdownexitinterface vlan 20ip address 192.168.20.1 255.255.255.0no shutdownexitinterface vlan 30ip address 192.168.30.1 255.255.255.0no shutdownexit

• Enable IP routing: ip routing

Step 4: Configure DHCP (Optional)

• If the core switch will provide DHCP for each VLAN:

  ip dhcp pool VLAN10network 192.168.10.0 255.255.255.0default-router 192.168.10.1exitip dhcp pool VLAN20network 192.168.20.0 255.255.255.0default-router 192.168.20.1exitip dhcp pool VLAN30network 192.168.30.0 255.255.255.0default-router 192.168.30.1exit

Step 5: Connect Access Switches or Routers

• Use trunk ports to connect access switches carrying multiple VLANs:

  interface GigabitEthernet0/24switchport mode trunkswitchport trunk allowed vlan 10,20,30exit

• If connecting to a router for Internet access, configure a VLAN interface as the default gateway and set a default route:

  ip route 0.0.0.0 0.0.0.0 <router-ip>

Step 6: Configure Redundancy and Port Channels (Optional)

• For higher availability, bundle multiple uplink ports using EtherChannel or LAG:

  interface range GigabitEthernet0/48-49channel-group 1 mode activeexitinterface Port-channel1switchport mode trunkswitchport trunk allowed vlan 10,20,30exit

• Enable Spanning Tree Protocol to prevent loops if multiple paths exist .

Step 7: Verify Configuration

• Check VLANs: show vlan brief
• Check IP interfaces: show ip interface brief
• Test inter-VLAN connectivity with ping between VLAN interfaces. By following these steps, your core switch will be configured to handle three separate networks with proper VLAN segmentation, routing, and optional DHCP services, ensuring efficient traffic management and scalability for future expansion .