Network of dry goods, whether it is operation or development are to know the Network Knowledge Series (ix)

Troubleshooting Network and Services

Example: Check the company's website for any problems.

1, you are the OPS personnel, the customer said to open the site slow, please analyze the possible reasons

A.ping www.muyuchen.com  ICMP protocol, (Freeway has no repair pass), Linux prohibit ICMP. ping-c3-i2-s512 www.baidu.comb.traceroute www.baidu.com  Basic inspection, each high-speed node has no repair pass. 　　 C.telnet www.etiatian.org Check the server Web is not open, the service is open   , and the firewall has no stall, (let not let this service through, so that you do not run to ride). Nmap 10.0.0.25-p  NC  : 1, 80 service is not open or port does not exist.

　　

2, FW Firewall blocked.

3. The port on which the service listens is not on the connected IP (127.0.0.1:25).

4, the ISP operator does not open the port by default, application opening port.

D.win: Trace Route

Tracert-d www.baidu.com

C:\users\oldboy>tracert-d www.qq.com

Up to 30 hops tracking

Routes to www.qq.com [182.254.18.159]:

  1     5 ms     1 MS     1 ms  10.0.0.254  2     8 ms     8 Ms    MS  115.33.32.1  3     5 ms     8 Ms     9 Ms  218.241.253.145  4 ms   4 ms  14.197.242.17  5     6 ms     8 Ms     7 MS  14.197.245.2  6     9 Ms    ten Ms  10.200.5.69  7    ms One    Ms  10.200.7.241  8 ms     8 ms     9 MS  10.200.5.82  9    each MS    MS  10.200.111.154 8 ms,     8 ms, 10.218.101.154     Ms  182.254.18.159

The trace is complete.

Grab Bag Scanning Tool

tcpdump command tcpdump-n icmp-i eth0nmapwindows:wireshark,sniffer, Koreb network analysis of several software

LAN machine is unable to solve the internet?

Interview questions: As the Enterprise network management, a local area network machine can not access the Internet, please give out the wrong idea?

Take Win32 Client as an example: how to Troubleshoot

Hint: Basic check idea, execute on Win32 client

(a) A single machine cannot access the Internet, others can

   A.ping www.baidu.com High-speed there is no repair pass     , but still can't surf the internet: may be browser, poisoning, agent and other issues.   the b.ping 10.0.0.254 Gateway is designed to exclude physical links (network cables, network cards, drivers, IP settings, etc.).    If the ping gateway does not work, view the IP settings, and then ping your own IP or ping the other machine IP in the network.            If the ping itself is out of IP: Check the IP settings, NIC drivers, physical links.            if the other machine IP in the ping network is on, the gateway does not allow you to network, or the gateway is wrong.   C.ping Gateway to the case, check the DNS settings are correct         1, check the method is, ping public IP, see patency (usually to remember a few external IP) ping 203.81.19.1.         2, host/dig/nslookup check the domain name resolution.   d. Internet router issues (configuration and hardware) and ISP line issues.     log in to route, check the superior line, call the ISP technology.   E. Auxiliary troubleshooting: Other people can surf the Internet, IP address conflict, ARP virus, core switch bad, switch loop (see log).　　

(b) The idea of a large area on the net

Routers, ISPs, core switches, ARP virus spoofing gateways, Gateway addresses are occupied, ldns problems.

The core switch is broken and the switch loops. The switch Mac/arp pool is full.

How to troubleshoot Web site opening slowly (80%)

Interview question: As a Linux operation, the customer reflects that opening your website server is very slow, how to debug (operation).

1, the website bandwidth problem. 2, the server CPU is too high. 3, the content resources are too large. 4, the user's bandwidth overload. 5, the website code has the problem. 6, the user line and the site line is not a problem. 7, the website server is attacked.

8. The total egress bandwidth or the associated server traffic (MRTG) of the hosted IDC room is not full. The 9.web server is not a high load. Io is high and the CPU is 10 high. is not the HTTP connection number to the upper limit, Apache default 150, you can see the error log. 11. Look at the backend database server is not load high load. The IO is high and the CPU is high. 12. Log in to the database to see if there are slow query statements show proceslist, adjust the MySQL configuration, and optimize the SQL statement. 13. Is the storage server, such as NFS,MFS load and disk IO high? 

Example: Check mu Yu Chen's website whether there is a problem.

(a) The user case, or all.

Oneself as the user to test, if no problem, from the customer's point of view to think. If you have a problem with your own test, follow the ideas below.

1 , the road is not a problem.

a.ping Www.muyuchen.org, the expressway has not been repaired.  If the ping is a pass, do not drop the packet. HTTP Service issues (service outage, service overloaded).  If the ping is a pass, drop the packet. The room bandwidth is not stable. Each line is unstable.    All sections of the-D www.oldboy.me are not repaired. Each line from the client to the server. Let the computer room cooperate to check.

First: User case, or all.

oneself as the user to test, if no problem, from the customer's point of view to think. If you have a problem with your own tests, follow the same line of thinking below. Line is normal problem a. Ping www.baidu.com               detects whether the ping line is normal if the ping is on, do not drop the packet. The problem with the HTTP service (the service is down, the service is overloaded) if the ping is on, but drops the packet. The room bandwidth is not stable. Each line is unstable. If Ping is not working, ping other URLs, if: computer room downtime, HTTP service problems (Service outage service overload)           -D www.baidu.com      Check trace parsing path is normal

Machine Room business is normal

the www.baidu.comor wget www.badu.com corresponds to the browser access D. Whether the server providing the service is overloaded with resources,         Excessive server and service connections, high load, high CPU, high IO

External issues

E. Whether the website purchase bandwidth is full, through the traffic monitoring service to view F. Chain outside chain (calling external Web site URL is problematic) tools for debugging the front-end of a Web site:1. Google Chrome                         F122 . Firefox firebug yslow                          3. IE HttpWatch

Other questions:

Individual customer problems, eg: the line of the user and the line of the website bandwidth does not match

Cluster architecture issues: (hundreds of servers serving)

G. Web service problem H. Database issues, log in to the database. See if there are slow query statements show proceslist, adjust MySQL configuration, optimize SQL statement I. Storage, and so on. is not a storage server, such as NFS MFS load and disk IO high

The network foundation must be written, oral, interview:

1, the TCP/IP protocol three handshake and four break process. 2. How the HTTP protocol works. 3, LAN machine can not be online troubleshooting. 4, the website opens slowly to troubleshoot (as Operation Dimension). 5, DNS and intelligent DNS resolution 6, OSI7 layer network model and each layer corresponding to the protocol 7, how to see the known port corresponding service name? 8. How does the route add a network route? 9, tcpdump capture Packet Troubleshooting (understanding) 10, IP Classification and subnetting (understanding) 11, Netstat output network status information, and the transition between different states. 12, the network connection by IP number of visits, the site IP corresponding PV access number. 13, timewait too much to solve.

　　

Disclaimer: As this article is based on books written blog, if you have a similar article blog, please contact me, I will be in the Declaration of origin.

Network of dry goods, whether it is operation or development are to know the Network Knowledge Series (ix)