The so-called software problems, the majority of IP parameter settings are wrong Ah, routing is not ah, there are DNS IP settings errors and so on, these problems are software settings! As long as the setting changes, using some detection software to find out, you know where the problem is! The basic questions are:
- Ip/netmask setting error on the network card:
For example: The same IP in the same network segment resulting in IP collisions, subnet mask set errors, network card driver use errors, network card IRQ, I/O Address settings conflict, etc.;
- Routing problem (route table):
The most common is the default gateway setting error! Or the routing interface does not match the problem caused by the data packet is not able to send out smoothly.
- Communication protocol does not match:
The most common communication transmission between different operating systems, such as "Net Fang" between the early Windows 98 and Windows 2000 to reach communication, Windows 98 must be installed NetBEUI this communication protocol. Another example of two Linux hosts to transmit data through the NFS communication protocol, both sides have to support rpcbind the RPC protocol to start the program only line! These communication protocols will be presented separately in the following chapters.
- Network load problem (loading):
When there are a large number of packets flooding the Server or the Hub or the same domain, it is possible to cause network pauses or even hang points! In addition, if someone in the network uses BT (peer software) or someone poisoning causes the worm to fill the whole area network, it will also cause the network pause problem;
- Other questions:
For example, some ports are blocked by firewalls, which can prevent certain network resources from being executed, bugs in the application itself, errors in the user's network settings in the application, compatibility issues with different operating systems, and so on.
Handling of the problem
Now that the problem has happened, we have to deal with him! So how do you deal with it? Take the Star online diagram above as an example to grasp two principles:
- First by their own environment detection, can be from the network card on their own PC, to the network line, to the hub and then to the modem and so on the hardware first check out. In this step, the best software is ping, and you'd better have more than two hosts to test online;
- Determine the hardware is no problem, and then to consider the software setup problem!
In fact, if the network is not working, you can do this in sequence:
- understand the question : Is this problem just happening? Or is it because of what I did before I couldn't get online? For example, before brother Bird has updated a core, the core does not drive the new network card of Brother Bird ...
- confirm IP: First look at your network card has no driver? Can I get the correct IP-related parameters to come online?
- Confirm Area Network connection : Use ping to communicate two host (router or IP share), determine network line and relay Hub/switch work properly;
- confirm the external online : Look at the host or IP-sharing device can be based on the fourth chapter of the method to obtain IP parameters, and ping method to determine the external connection can be successful (such as Ping 168.95.1.1);
- Confirm DNS Query : Check www.google.com with nslookup or host or dig;
- Confirm Internet Nodes : Can I use traceroute to check each node for no problem?
- confirm the normal service of the other server : is the other server busy? Or is his machine hung up?
- confirm our server : If it is not connected to my host, then check the host some of the services correctly started no? can be checked with netstat. or whether certain security mechanisms of the software are not set up, such as the SELinux mechanism;
- firewall or permissions issue : Is it due to permission set error? Is it because your machine has a firewall that forgets to enable a port that can be brought online? This can be handled through tcpdump!
After these processing actions, generally speaking, you should be able to solve the problem you can not access the internet! Of course, if it's a hardware problem, what you probably need most is ... "Get it repaired, kid!" "
Linux Network debug: Unable to online cause analysis
