Network Troubleshooting Commands

Layer 1: The Physical Layer

  • Show interface status:

    1
2
3

    ip link show
ip link set eth0 up
ip -br link show

  • Show interface statistics:

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    ip -s -h l show dev enp1s0

  • Check interface speed with ethtool:

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    ethtool eth0

  • Address Resolution Protocol (ARP):

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    ip neighbor show

  • Delete ARP entry:

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    ip neighbor delete 192.168.122.170 dev eth0

Layer 3: The Network/Internet Layer

  • Show IP addresses:

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    ip -br address show

  • Ping utility for testing connectivity:

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    ping 192.168.122.1

  • Trace the route to a host:

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    tracepath -n sat65server

  • Show routing table:

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2

    ip route show
ip route show 10.0.0.0/8

Layer 4: The Transport Layer

  • Check listening ports and associated processes:

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2

    ss -tunlp4
sudo ss -tnlp

  • Check TCP connections:

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    ss dst 192.168.122.1

  • Test UDP port with netcat:

    1

    nc 192.168.122.1 -u 80

Notes:

  • The tracepath command is used to display the network connectivity path between the local host and a remote host, identifying all routers in the path.
  • ARP helps resolve IP addresses to MAC addresses, and the ARP table can be manipulated using the ip neighbor command.
  • Tools like ping and traceroute are crucial for testing network connectivity and identifying routes between hosts.