Network troubleshooting - Step by step (Why is the server not connected to the network?)
| F.A.Q.Network troubleshooting - Step by step
- Why is the server not connected to the network?
- Why isn't the Internet working?
Before you call the NOC check..
Diagnostic tools needed
- ipconfig (Windows)
- ip (Linux)
- ping (Windows i Linux)
- arp (Windows i Linux)
- arp-scan (Linux)
- tracert (Windows)
- traceroute (Linux)
- mtr (Linux - mtr acts as a real-time traceroute)
- netstat (Windows i Linux)
- tcpdump (Windows i Linux)
- wireshark (Windows i Linux)
How does the Internet work?
- HTTP is based on TCP,
- TCP is based on the IP protocol
- IP is based on the Ethernet protocol,
- and Ethernet requires a network cable.
- IP is based on the Ethernet protocol,
- TCP is based on the IP protocol
Diagnostics
Start the analysis from the lowest or highest layer of the stack (ISO/OSI Model)
- Are the wires plugged in correctly and is the link control LED on to confirm that the connection has been set up?
- Is the network interface configured correctly?
-
ipconfig /all(Windows)ip a(Linux)
- Do the arp tables contain information about other hosts?
arp a(Windows)arp(Linux)
- Is a firewall running on the machine?
- Windows Defender
iptables -nvL(Linux)
- Is there a firewall running between the client and the target host?
- Do firewalls allow ICMP packets (ping)
iptables -A INPUT -p icmp -i eth0 -j ACCEPT(Linux)
- Does the ping 127.0.0.1 command work?
- Does the ping command to other hosts on the local network by their name work?
- Is DNS working properly?
tracert www.serverparts.pl(Windows)mtr www.serverparts.pl(Linux)
- Does the ping command to other hosts on the local network by their IP address work?
- Does the ping command to hosts on another network work?
- Are higher network layer services SSH (22), WWW (80) working)?
- Wireshark (Windows)
tcpdump -i eno1 tcp port 22(Linux)tcpdump -i eno1 tcp port 80(Linux)
- Has the firewall configuration been checked?
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