When a cloud server experiences network disruption or websites hosted on the cloud server become inaccessible, there can be multiple reasons behind it. Everyday, we surf the internet without realizing the many steps involved in successfully accessing a website. A problem in any of these steps can lead to website accessibility issues. Below, we analyze these issues from the inside out, providing a reference for troubleshooting.

Layer 1: Reasons Pertaining to the Website Itself

• Errors in website program design.
• Website hacked due to program vulnerabilities or lack of updates.
• Abnormal domain name resolution.
• Domestic servers without proper domain registration.

Layer 2: Internal Reasons within the Cloud Server

• Network card disabled due to misoperation.
• Incorrect settings of IP address, subnet mask, default gateway, etc.
• Incorrect settings for routing and remote access.
• Improper configuration of third-party security software, such as 'Safety Dog'.
• Operating system hacked, website infected with trojans.
• High CPU usage, load, or memory usage on the cloud server.
• The cloud server is under external DDoS or CC attacks.
• Serious legal violations by the cloud server, leading to disconnection or IP blocking by the data center.

Layer 3: Reasons Related to the Cloud Server's Data Center

• Other servers in the data center under DDOS attacks, consuming significant bandwidth.
• Data center relocation, routine maintenance, and other foreseeable factors.
• Data center power outages, floods, earthquakes, and other force majeure events.

Layer 4: Reasons Involving Basic Telecommunications Operators

• Foreign IP addresses blocked by national firewalls.
• Telecommunications department network maintenance or cable cutting.
• Network failures due to routing node issues or submarine cable problems.

Layer 5: Reasons Related to the Customer's Own Computer

• Customer's computer infected with a virus, leading to abnormal access to most websites.
• Slow website access due to the customer's computer using software like Xunlei for downloading.
• Problems in the line between the customer's broadband and the data center, which can also be attributed to the basic telecommunications operator.