Configuring a trunk on a switch s optical port

To configure a Cisco switch optical port as a trunk, set the interface to trunk mode, specify 802.1Q encapsulation, and define allowed VLANs.Step-by-Step ConfigurationAccess the Switch CLIConnect via console, SSH, or Telnet.Enter privileged EXEC mode:CodeCopyenable Enter global configuration mode:CodeCopyconfigure terminal Select the Optical InterfaceIdentify the optical port (e.g., GigabitEthernet1/1 or TenGigabitEthernet1/1):CodeCopyinterface GigabitEthernet1/1 Specify Trunk EncapsulationSet the encapsulation to IEEE 802.1Q (industry standard):CodeCopyswitchport trunk encapsulation dot1q Note: Some older switches may require enabling dot1q explicitly before trunking.Set the Port to Trunk ModeConfigure the interface as a permanent trunk:CodeCopyswitchport mode trunk Avoid dynamic modes (dynamic auto or dynamic desirable) for security and predictability.Configure Allowed VLANsSpecify which VLANs can traverse the trunk:CodeCopyswitchport trunk allowed vlan 10,20,30 This ensures only required VLAN traffic passes through the trunk.Set the Native VLANFor security, assign a native VLAN that is unused:CodeCopyswitchport trunk native vlan 1001 Frames without a VLAN tag will be assigned to this VLAN.Verify the ConfigurationExit interface configuration mode:CodeCopyend Check trunk status:CodeCopyshow interfaces trunkshow running-config Save the ConfigurationCodeCopywrite memory orCodeCopycopy running-config startup-config Best PracticesDisable DTP if connecting to non-Cisco devices to prevent unwanted trunk negotiation.Ensure VLAN consistency on both ends of the trunk to avoid spanning-tree loops.Use 802.1Q instead of ISL for interoperability with modern devices.Verify loop-free topology before enabling trunking on production networks. By following these steps, the optical port will carry traffic for multiple VLANs, enabling efficient inter-switch communication and VLAN extension across the network .