Network Troubleshooting for Linux

First, the hardware problem
1, the problem of network cable
Class A type B straight line and crossover
Network cable is truncated
Bad signal due to excessive distortion of network cable
Poor quality of homemade network interface
Poor network interface and device contact

2, Nic, Hub, and router network equipment problems
Network card instability, poor quality, compatibility issues
Network Equipment Connector Poor quality, poor contact, resulting in model attenuation
Network equipment is in a bad environment causing downtime
Poor use of network equipment, resulting in device function attenuation

3. Rules for device configuration
Using the wrong network cable
Erection of the cable is too long
Interference of other noises
Too many nodes or other devices on the LAN

Second, software problems
1. Ip/netmask setting error of NIC
2. Routing problems (Router Table)
3, communication protocol does not match
4, the problem of Network load
5. Other issues

Third, problem-handling
1, understand the problem: whether a wrong operation caused the network is not working.
2, Confirm IP: Network card is working properly, whether to obtain the correct IP
3. Confirm LAN Connection: use Ping to test
4. Confirm External connection: Ping gateway
5. Confirm DNS query: nslookup, host, dig
6. Confirm Internet node: traceroute
7, confirm the other server: whether the other server is too busy or downtime
8, confirm our server: Check whether the service is working properly, netstat
9. Firewall or permissions issues: Iptables, rwx, SELinux, tcpdump

Network Troubleshooting for Linux