[TechNotes] Troubleshooting Internet Access Failures

【Introduction】

As the Internet is booming nowadays, Internet access has become an essential part of our life. Hundreds of millions of people access the Internet anytime and anywhere. However, most people do not understand Internet access technologies, except for some network professionals. This document focuses on troubleshooting Internet access failures. Before troubleshooting, you need to get insights into basic Internet access concepts, process, and modes, which will help you better locate and handle faults.

【Contents】

As mentioned above, ARs play an important role in the Internet access process of enterprise users. This document describes how to troubleshoot faults of enterprise routers that may cause Internet access failures. WAN-side and terminal-side faults are not described in this document. The troubleshooting methods and solutions in this document are summarized based on actual cases on the live network, regardless of Internet access modes.

Scenario	Scenario Description	Possible Causes	Troubleshooting Method
Failure to access the Internet after deployment	Internet access failures occur in the deployment phase when an AR is connected to the Internet for the first time. After deployment personnel configure the Internet access function on the AR for the first time, users cannot access the Internet.	This is mostly because Internet access configurations are incorrect. For example, NAT is not enabled, the default route is not configured, or the DHCP configuration is incorrect.	Check whether the corresponding configurations are correct by referring to 1.6 .
Failure to access the Internet during AR running	Internet access failures occur when the AR has been successfully deployed and running properly for a period of time. At a certain time point or during a certain period of time, users cannot access the Internet.	This is mostly because unexpected events occur, such as hardware faults, public DNS exceptions, ARP attacks, IP address conflicts, and route unreachability.	Check whether the corresponding configurations are correct by referring to 1.7 .