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Solution: Server Cabled to Wrong Switch Port

Triage

  1. Identify where the server is actually connected:
  2. lldpctl or lldptool -t -n -i eno1 on the server
  3. Note the reported switch chassis name and port ID
  4. Compare with the cabling plan:
  5. Expected: sw-tor-c12 Eth1/33 (VLAN 320, production)
  6. Actual (from LLDP): sw-tor-c12 Eth1/9 (VLAN 50, development)
  7. Verify the target port (Eth1/33) is ready:
  8. On the switch: show running-config interface Eth1/33
  9. Confirm it is configured for VLAN 320 and not in use
  10. Check the current IP and DHCP state:
  11. ip addr show eno1 -- note the 172.16.50.x address
  12. This address is from the dev VLAN DHCP scope

Root Cause

The contractor plugged the server's network cable into switch port Eth1/9 instead of Eth1/33. The cable label reads "C12-P33" (correct), but the physical cable follows the wrong path in the cable management tray and terminates at Eth1/9. The ports are in different patch panel sections, and the contractor likely miscounted ports in the dense patch panel.

Port Eth1/9 is an active port configured for VLAN 50 (development). The server received a DHCP address from the dev VLAN scope and came up on the wrong network segment.

Fix

  1. Verify the target port:
  2. On the switch: show interface Eth1/33 brief -- confirm status is "notconnect" (empty port)
  3. show running-config interface Eth1/33 -- confirm VLAN 320 configuration
  4. Move the cable:
  5. Physically trace the cable from the server's NIC to the switch
  6. Unplug from Eth1/9 and plug into Eth1/33
  7. This is a brief network interruption (seconds)
  8. Renew the IP address:
  9. dhclient -r eno1 && dhclient eno1 -- release old, request new
  10. Or if using NetworkManager: nmcli con down eno1 && nmcli con up eno1
  11. Verify connectivity:
  12. ip addr show eno1 -- should now show 10.30.20.x
  13. ping 10.30.20.1 -- gateway reachable
  14. lldpctl -- should now report Eth1/33
  15. Update cable management:
  16. Re-label the cable if the label is misleading
  17. Physically re-route the cable through the correct cable management tray
  18. Take a photo of the final cabling for documentation
  19. Audit the batch:
  20. Check all other servers installed during the same contractor shift
  21. Run lldpctl on each and compare with the cabling plan
  22. Fix any other mismatch before those servers go into production

Rollback / Safety

  • Moving a network cable is non-destructive; the worst case is a few seconds of packet loss.
  • If Eth1/33 turns out to be misconfigured, the server will get no link/IP; just move the cable back and fix the switch config.
  • The server was briefly on the dev VLAN; check if any dev traffic reached the server or if the server's DHCP lease created conflicts on the dev subnet.

Common Traps

  • Reconfiguring the switch instead of moving the cable: Changing Eth1/9 from VLAN 50 to VLAN 320 "fixes" this server but breaks whatever was supposed to be on Eth1/9.
  • Not checking if Eth1/9 is assigned to another server: If another server should be on Eth1/9, you may have displaced it. Verify.
  • Trusting cable labels blindly: Labels can be wrong. Always verify with LLDP or physical trace.
  • Forgetting DHCP lease cleanup: The old DHCP lease on the dev VLAN will persist on the DHCP server until it expires. Not harmful but messy.
  • Not auditing the rest of the batch: If one cable is wrong, others from the same install are suspect.