Configure the connection between two switch optical ports

To connect two switches via fiber, ensure compatible SFP/SFP+ modules, matching fiber type, proper connectors, and configure interfaces correctly, optionally using EtherChannel for redundancy.

Step 1: Choose the Right Fiber and SFP Modules

• Fiber Type: Use multimode fiber for short runs (under 1000 feet / ~300 meters) and single-mode fiber for longer distances (over 1000 feet) .
• SFP/SFP+ Modules: Select modules that match the fiber type and desired speed. 1G modules are SFP, 10G modules are SFP+, and higher speeds use QSFP .
• Wavelength and Duplex: Ensure both switches use the same wavelength and duplex mode. For duplex fiber, connect send on one port to receive on the other .

Step 2: Connect the Fiber

• Use LC-LC connectors for most modern SFP modules .
• Verify that the fiber strands are correctly crossed: transmit (TX) on switch A to receive (RX) on switch B.
• Check that the fiber length does not exceed the module's maximum transmission distance .

Step 3: Configure Switch Interfaces

• Enable the SFP interfaces:

  interface GigabitEthernet1/0/1no shutdown

• Assign VLANs if needed. By default, VLAN 1 is used, but you can configure trunking for multiple VLANs:

  switchport mode trunkswitchport trunk allowed vlan 10,20

• Verify the link status with show interface status or show ip interface brief .

Step 4: Redundancy and Aggregation

• For redundancy, run two fiber links between switches and configure EtherChannel (port-channel) to prevent loops and increase bandwidth:

  interface range GigabitEthernet1/0/1 - 2channel-group 1 mode active

• Avoid connecting multiple switches in a full mesh without proper spanning-tree configuration to prevent loops .

Step 5: Troubleshooting

• If the link does not come up, check:
  • SFP module compatibility (Cisco devices may reject third-party SFPs) .
  • Fiber type and connector correctness.
  • Duplex and speed settings match on both ends.
• Replace faulty SFPs or patch cords if necessary .

Best Practices

• Use matching SFP modules and fiber types for both switches.
• Keep fiber runs within recommended distances.
• Use EtherChannel for redundancy rather than multiple independent links to avoid loops.
• Document the topology and label fiber connections for maintenance. By following these steps, you can establish a reliable, high-speed optical interconnection between two switches, supporting VLANs, redundancy, and future scalability.