Test connectivity for the web service

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find the problem occurred: (1) local service at the server (localhost) (2) from LAN to server (3) from WAN to server


Connecting from the local machine to web service at the same server

WAN ○ -------> ○ LAN -------> ● server

  If you has administrative permission to log into the server via SSH or Remote desktop service.

Check if your computer/server Is being assigned the IP Address

  • Linux   : (1) Check the IP Address. ifconfig. (2) Re-assign the IP Address and restart the networking service. service network restart for CentOS[1]
  • Win   : Check the IP Address. ifconfig/all
  • More on Network problem

Is the service alive or the port was occupied by other process?

Check the port if used by other protocol

Find process running on port

  • Linux  
    • nmap "Network exploration tool and security / port scanner." e.g. nmap -p 80,443 ip
    • ss "utility to investigate sockets" e.g. ss -tnlp | grep 80 or using OR operator[2] ss -tnlp | grep '80\|443'
    • ps List the current processes. Input ps -aux | grep "PORT_NUMBER" e.g. ps -aux | grep 443
    • netstat Command netstat -tulpn | grep LISTEN e.g.
  • Win   Using the software CurrPorts to check the process and port. e.g. Apache will not running if the 80 port was occupied by skype[3].
$ netstat -tulpn | grep LISTEN

tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      - 

// means the 80 port service is running

Is the port opened for external users?

Check the OS firewall or protected by antivirus software

    • Linux  
      • iptables: (1) iptables -L to list all rules[4] (2) rule with smaller line-number will override the rule with larger line-number[5]
      • FirewallD rules: (1) sudo firewall-cmd --get-default-zone return 'public' (2) sudo firewall-cmd --list-all --zone=public[6] (3) Allow port with FirewallD
      • SELinux Policy Management: (1) After installed policycoreutils-python[7], input semanage port -l to list open ports. (2) Allow port with semanage.
    • Win   Windows Firewall with Advanced Security -> configure firewall rules
    • protected by antivirus software?
  • connect to localhost ex: telnet 127.0.0.1 23 where 23 is the port number where the service running
  • double check the server/service logs

Connecting from LAN to the server

WAN ○ -------> ● LAN -------> ● server

Testing on LAN (local network, subnet scope): The different servers between LAN or with the same ip class (ex: 1.2.3.*) may not have the firewall limit.

  • Is the service alive?
  • Connect to the internal IP eg: telnet 172.18.0.1 23 (1) IP start with 172.18... is Private IP Network Numbers (2) where 23 is the port number where the service running
  • If the local service is web server, you can also try to connect the internal IP e.g. lynx http://172.18.0.1 for Linux  
  • Double check the server/service logs
  • Is the internal IP correct?

Connecting from WAN to the server

WAN ● -------> ● LAN -------> ● server

How to connect to remote web service

Open the browser from outside network ex: Wide Area Network (WAN) or Local Area Network (LAN)

  • and type the address: http://the.domain Icon_exclaim.gif Note: Not Private network / Private IP address
  • or use the remote website monitoring services: Web Ping

Using alternative web services if the Python was installed

  • (for python 2.x) python -m SimpleHTTPServer <port>[8]
  • (for python 3.x) python -m http.server <port>[9]

Using telnet client

curl

  • curl -v -o /dev/null http://IP:Port If failed. It will show the message: "failed: Connection refused"

other issues

We met the trouble on WAN (wide area network). If we do no have the administrative permission, the tests we can do as follows:

other issue:

Tools

  1. Good.gif CurrPorts: Monitoring TCP/IP network connections on Windows
  2. PFPortCheck Program: check TCP/UDP port from localhost(where you installed the program) to portforward.com
  3. TCPView for Windows
  4. Check server: Check host - online website monitoring, Check IP "checks the possibility of a TCP connection to host's specified port from different locations around the world." quoted from website. [Last visited: 2015-08-02]

References

  1. ↑ How to restart the networking service? - Ask Ubuntu
  2. ↑ 7 Linux Grep OR, Grep AND, Grep NOT Operator Examples
  3. ↑ How to solve WAMP and Skype conflict on Windows 7? - Stack Overflow
  4. ↑ HowTos/Network/IPTables - CentOS Wiki
  5. ↑ How to edit iptables rules - FedoraProject
  6. ↑ How To Set Up a Firewall Using FirewallD on CentOS 7 | DigitalOcean
  7. ↑ semanage command not found on CentOS 7 and RHEL 7
  8. ↑ 20.19. SimpleHTTPServer — Simple HTTP request handler — Python 2.7.17 documentation
  9. ↑ http.server — HTTP servers — Python 3.8.1 documentation
  10. ↑ networking - Command for determining my public IP? - Ask Ubuntu


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