Test connectivity for the web service

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

🌐 Switch language: EN, 漢字

How to connect to the web service edit

If the service is the web server:

(1) Open the browser, (2) Type the address: http://127.0.0.1 or http://the.domain

Linux lynx command:
1. (optional if lynx was not installed) yum install lynx for CentOS / sudo apt-get install lynx for Ubuntu^[1]
2. lynx http://127.0.0.1 ^[2] for Linux

telnet command
1. telnet 127.0.0.1 <PORT> e.g. telnet 127.0.0.1 80 or telnet the.domain 80
2. (after telnet-ed the web 80 port, key in) get + SPACE^[3]

curl^[4]: curl -vL http://IP:Port
- (optional if curl command was not installed) Learn how to install & run cURL on Windows/MacOSX/Linux | Ubidots Help Center
- commands e.g.
  - (1) Write output to <file> instead of stdout using curl -voL https://www.google.com
  - (2) Write output to stdout using curl -vL https://www.google.com or curl -voL /dev/null https://www.google.com
  - (3) Write output to <file> with the remote file name using curl -vOL https://www.google.com/index.html
- If failed. It will show the message: "failed: Connection refused"

Linux wget software e.g. wget https://www.google.com

use the third-party website monitoring the services: Web Ping

If the service is not the web server, use telnet instead

(optional) Install Telnet Client | Microsoft Docs on Win . Bring telnet back on macOS high Sierra – Ayuth Mangmesap (blackSource) – Medium on macOS
telnet 127.0.0.1 <PORT> If failed to connect the web service. It will show the message: "telnet: Unable to connect to remote host: Connection refused"

Using alternative web services if the Python or Node.js was installed

(for python 3.x) python -m http.server [port] (default port: 8000)^[5]
(for Node.js) npx http-server [-p port] (default port: 8080)^[6]

Test connectivity for the local web service edit

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 edit

Linux : (1) Check the IP Address. ifconfig. (2) Re-assign the IP Address and restart the networking service. service network restart for CentOS^[7]
Win : Check the IP Address. ifconfig/all
More on Network problem

Check if web service has started successfully? edit

Apache /etc/init.d/httpd status on CentOS7 ^[8]
nginx sudo service nginx status on CentOS7
Docker container docker ps to check if the container is running & expose the port^[9]

Check if MySQL has started successfully? edit

Using lsof command edit

lsof -i:3306 on macOS or Linux

The command lsof -i:3306 is used in Unix-like operating systems to list open files and the processes that opened them. Let's break down the command:

lsof: This stands for "List Open Files". It's a command-line utility that displays information about files opened by processes. In Unix and Linux, everything is treated as a file (including hardware devices, sockets, and directories), so lsof is a powerful tool for system administrators to monitor and troubleshoot system behavior.

-i: This option tells lsof to show only network files. In Unix and Linux, network connections are treated as files. The -i option can be used to filter connections based on the Internet address or network protocol.

3306: This specifies the port number. Port 3306 is commonly used by MySQL, a popular database management system. By including :3306, you are asking lsof to list all network files (which includes socket connections) that are associated with port 3306.

Example output: localhost:mysql (LISTEN) means the MySQL has started successfully

COMMAND     PID      USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
mysqld    93034 account   29u  IPv4 0xxxx      0t0  TCP localhost:mysql (LISTEN)

Using ps command edit

ps aux | grep mysql on macOS

Example output if MySQL has started successfully:

_mysql           11083   0.3  0.2 409657280  31424   ??  Ss    2:12下午   0:01.07 /usr/local/mysql/bin/mysqld --user=_mysql --basedir=/usr/local/mysql --datadir=/usr/local/mysql/data --plugin-dir=/usr/local/mysql/lib/plugin --log-error=/usr/local/mysql/data/mysqld.local.err --pid-file=/usr/local/mysql/data/mysqld.local.pid --keyring-file-data=/usr/local/mysql/keyring/keyring --early-plugin-load=keyring_file=keyring_file.so
ACCOUNT        12349   0.0  0.0 408645328   1648 s011  S+    2:14下午   0:00.00 grep mysql

Example output if MySQL has NOT started successfully:

ACCOUNT        12349   0.0  0.0 408645328   1648 s011  S+    2:14下午   0:00.00 grep mysql

Check if a port was occupied by other process? edit

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^[10] 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.
- docker port | Docker Documentation

Example output of netstat command

$ netstat -tulpn | grep LISTEN

tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      - 

// means the 80 port service is running

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^[11].

Check if a port is blocked by browser edit

Check if a port is blocked by browser^[12]

Chrome net/base/port_util.cc - chromium/src.git - Git at Google
Fetch Standard 2.9. Port blocking

Is the port opened for external users? edit

Check the OS firewall or protected by antivirus software

- Linux
  - iptables: (1) iptables -L to list all rules^[13] (2) rule with smaller line-number will override the rule with larger line-number^[14]
  - FirewallD rules: (1) sudo firewall-cmd --get-default-zone return 'public' (2) sudo firewall-cmd --list-all --zone=public^[15] (3) Allow port with FirewallD
  - SELinux Policy Management: (1) After installed policycoreutils-python^[16], 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
- Install Telnet Client on Win
- if the local service is web server, you can also try lynx http://127.0.0.1 for Linux
double check the server/service logs

Test connectivity from LAN to the server edit

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.*) and may not have the firewall limit. Private network / Private IP address

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?

Test connectivity from WAN to the remote server edit

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

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

Down for everyone or just me? more on Web Ping
Switch to different ISP? Is hardware firewall enabled?
Is gateway alive?
Is DNS alive?
Is the external IP correct?
- If the firewall rule is IP specified, verify the IP if correct from What Is My IP Address? or web access log.
- Query the IP Address Details - ipinfo.io. e.g. Input the command curl ipinfo.io/ip^[17] for macOS & Linux
Is the port was opened for external users? Open Port Check Tool - Port Forwarding Port Check Tool
Is institutional/ISP firewall enabled? Contact your MIS. (Management information system) of your company or ISP?

other issue:

bandwidth cost too much by certain users
exceed the request limit of (hardware) firewall
the external connection of updated Windows was down until reboot Win
Amazon EC2 security group
refresh browser cache: Refresh your cache - When hitting F5 just isn't enough!

Tools edit

CurrPorts: Monitoring TCP/IP network connections on Windows
PFPortCheck Program: check TCP/UDP port from localhost(where you installed the program) to portforward.com
TCPView for Windows
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 edit

Troubleshooting of ...

Troubleshooting of Excel errors

PHP, cUrl, Python, selenium, HTTP status code errors

Database: SQL syntax debug, MySQL errors, MySQLTuner errors or PostgreSQL errors

Troubleshooting of regular expression

HTML/Javascript: Troubleshooting of javascript, XPath

Software: Mediawiki, Docker, FTP problems, online conference software

Test connectivity for the web service, Web Ping, Network problem, Web user behavior, Web scrape troubleshooting

Template

Bug report template

[1] Install and Use Lynx Browser on Ubuntu

[2] Lynx Users Guide v2.8.7

[3] HTTP Check Port 80 with the Telnet Command

[4] url - How To Use

[5] ttp.server — HTTP servers — Python 3.8.1 documentation

[6] ttp-server: a simple static HTTP server

[7] How to restart the networking service? - Ask Ubuntu

[8] How to check running status of LAMP stack | E2E Networks Knowledgebase

[9] r ps | Docker Documentation

[10] 7 Linux Grep OR, Grep AND, Grep NOT Operator Examples

[11] How to solve WAMP and Skype conflict on Windows 7? - Stack Overflow

[12] 開發與部署網站時需注意不要使用到 ERR_UNSAFE_PORT 不安全的埠號 | The Will Will Web

[13] HowTos/Network/IPTables - CentOS Wiki

[14] How to edit iptables rules - FedoraProject

[15] How To Set Up a Firewall Using FirewallD on CentOS 7 | DigitalOcean

[16] semanage command not found on CentOS 7 and RHEL 7

[17] tworking - Command for determining my public IP? - Ask Ubuntu

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

[16]

[17]