4.6 Given a scenario, troubleshoot and resolve common network issues - Paiet/Tech-Journal-for-Everything GitHub Wiki

4.6 Given a scenario, troubleshoot and resolve common network issues

  • Incorrect IP configuration/default gateway
    • Scenario: bad subnet mask, bad ip address
    • Simple Diagram
    • Demo (Mike)
      • Use client01 VM
      • Misconfigure subnet mask
      • Try to connect to \\dc01\corpdocs
  • Broadcast storms/switching loop
    • Scenario: multiple switches connected together an form a loop
    • Simple Diagram
    • Solution: Spanning Tree Protocol
  • Duplicate IP
    • Scenario: Using DHCP and Static IPs on the same network or new lease before old lease expires
    • Demo (Mike)
      • Use client VMs
      • Client02 is using DHCP
      • Client01 statically mapped to same IP address
  • Speed and duplex mismatch
    • Scenario: Human Error to be corrected.
    • Demo (Ronnie)
  • End-to-end connectivity
    • Scenario: assumptions that everything must be working working correctly.
    • Demo (Mike)
      • Disable NIC on client01
  • Incorrect VLAN assignment
    • Scenario: simple misconfiguration, or wrong port plugged in.
    • Simple Diagram
  • Hardware failure
    • Scenario: End of Life, PSU Failure, Flapping NIC
    • replace the equipment on a life cycle rather than at time of failure
  • Misconfigured DHCP
    • Scenario: Rogue DHCP server, wrong IP helper address
    • Demo (Mike)
      • Use dc01
      • Configure DHCP to pass out wrong subnet mask
  • Misconfigured DNS
    • Scenario: Wrong forwarder, wrong DNS, no reverse zone
    • Demo (Mike)
      • Use dc01
      • Configure wrong forwarder
  • Incorrect interface/interface misconfiguration
    • Scenario: User Error
    • Demo (Ronnie)
  • Cable placement
    • Scenario: Structural issues, interior and external walls. UTP implemented close to HVAC or too close to electrical motors or fluorescent lamps.
  • Interface errors
    • Scenario: Physical-wrong cable, Logical-misconfigurations
  • Simultaneous wired/wireless connections
    • Scenario: Wired Network and Wireless are configure for different default gateways
  • Discovering neighboring devices/nodes
    • Scenario: ???
  • Power failure/power anomalies
    • Scenario: Power Outage, power spikes
  • MTU/MTU black hole
    • Scenario: Filtering PTB (Packet to Big) packets and IP fragment. (Firewalls configured this way)
    • Result is that the end user believes this is the fault of the application they're using, the remote server is down or that the path is unreachable.
    • Firewall may be discarding all ICMP packets this prevents path discovery from working correctly.
  • Missing IP routes
    • Scenario: Dynamic routing protocol misconfigured, no Static Route
    • Demo (Ronnie) static routing, configure one but not the other way
  • NIC teaming misconfiguration LBFO (Load Balancing / Failover)
    • Active-active vs active-passive
      • Active-active - load balancing
      • active-passive - one is on standby
    • Multicast vs broadcast
      • NIC team normally uses multicast to transmit and receive.
      • NIC teams can be configured to operate on broadcast
      • Usually both NICS must be set to use the same method