Troubleshoot Wired Connectivity

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• A client wired connectivity issue means that either:
  • the network adapter does not establish a network link at all (no connectivity)
  • or the connection is unstable or intermittent
• establish that the problem affects a single host only
  • then isolate the precise location of the physical issue

Troubleshoot Cable and Network Adapter Issues

• typical Ethernet link for an office workstation includes the following components:
  • NIC port on the host
  • RJ45 terminated patch cord between the host and a wall port
  • Structured cable between the wall port and a patch panel
    • terminated to insulation displacement connector (IDC) blocks (the permanent link)
  • RJ45 terminated patch cord between the patch panel port and a switch port
  • Network transceiver in the switch port

Info

The link LEDs on network adapter and switch ports will indicate whether the link is active and possibly at what speed the link is working. The LEDs typically flicker to show network activity.

Steps

1. check that the patch cords are properly terminated and connected to the network ports
   • If you suspect a fault, substitute the patch cord with a known good cable
   • verify patch cords using a cable tester
2. If you cannot isolate the problem to the patch cords, test the transceivers
   • use a loopback tool to test for a bad port
3. If you don’t have a loopback tool available, another approach is to substitute known working hosts
   • connect a different computer to the link or swap ports at the switch
   • This method may have adverse impacts on the rest of the network
     • issues such as port security may make it unreliable
4. If you can discount faulty patch cords and bad network ports/NICs, use a cable tester to verify the structured cabling
   • solution may involve installing a new permanent link, but there could also be a termination or external interference problem
   • advanced type of cable tester called a “certifier” can report detailed information about cable performance and interference
5. If there is no issue in the structured cabling, verify the Ethernet speed/duplex configuration on the switch interface and NIC
   • should usually be set to autonegotiate
   • try updating the NIC’s device driver software

Troubleshoot Port Flapping Issues

• Intermittent connectivity might manifest as port flapping
  • the NIC or switch interface transitions continually between up and down states
• often caused by:
  • bad cabling
  • external interference
  • a faulty NIC at the host end
• use the switch configuration interface to report how long a port remains in the up state