How to use the Online Detection feature to test the WAN link?

The Online Detection feature is used to test specific WAN link is online or not, and talking about ‘online’, there are two circumstances of ‘online’ on the Online Detection feature:

1.    Whether a specific WAN port could get through its front-end gateway

2.    Whether a specific WAN port could get through some specific address

 

Besides, there are two modes of Online Detection:Auto mode&Manual Mode

 

Let’s take an example of the scenario below:

The topology describes a most commonly used network environment in our daily life. Three users’ PCs connect to the LAN ports of TL-ER6120, aiming to use two WAN links to access the Internet through two front-end gateways.

We assume the links from WAN1 gateway and WAN2 gateway to Internet are both broken, and in order to use our router to detect the status of the two links, and illustrate what’s the difference between them, here we configure WAN1 as Auto mode and WAN2 as Manual mode.

 

Step 1 From main menu, select “Maintenance”---“Diagnostics”---“Online Detection”

 

 

Step 2 Choose Port as “WAN1”, select Detecting as “Activate”, and Mode as “Auto”, here you may see the “Ping” and “DNS Lookup” are set in gray, you are unable to modify them here.Click on Save, the entry will be added.

 

 

Step 3 Choose Port as “WAN2”, select Detecting as “Activate”, and Mode as “Manual”, and you can set an IP address in “ping” and another IP address in“DNS Lookup”, here we both set 8.8.8.8 as an example, which is the address of Google DNS server and needs Internet to get access. Click on Save, the entry will be added.

 

 

OK let’s see the result of Status:

 

 

The status of the two entries displayed on WAN1 and WAN2 are different. The router is using the same kind of link for accessing Internet attached to the WAN ports but why the results are different?

 

It is the working principle of “Online Detection” that matters:

 

1.    Auto mode means the WAN port will detect the way to the front-end gateway, no further routing detection. See the picture below,the way between WAN1 gateway to Internet has been broken, but for WAN1 port, it can ping WAN1 gateway successfully, and it will receive DNS lookup replying from WAN1 gateway, so the “ping” and “DNS lookup” to front-end gateway are both available, that’s why WAN1 is considered as “Online”

 

 

2.    Manual mode means the WAN port will detect the way to a specific IP address you set, no matter whatever you set, the WAN port will detect the link to the IP address by two methods: 1. Ping 2. DNS Lookup

In this case, we both set 8.8.8.8 for ping and DNS lookup, so the router will send ICMP ping packet to 8.8.8.8 and DNS lookup packets to 8.8.8.8, as the Internet link is broken, the ping and DNS lookup will be both absolutely failed, that’s why “Online Detection” shows WAN2 as“failed”.

 

Explanation the result of link Status:

 

Online: Either ping or DNS lookup, if either of them get success, the WAN link will be judged as “Online”

Failed: Only if both ping and DNS lookup are failed, the WAN link will be judged as “Failed”

 

 

When should we use Auto mode or Manual mode?

 

It depends on destination IP address you would like to ping and DNS lookup.

When you want to make sure the WAN port could get through its front-end gateway, you can select Auto mode without setting any specific destination IP address; when you want to make sure the WAN port can get through a specific IP address or get internet access, you can select Manual mode and set the specific IP Address or public IP Address like the example above.Of particular note is only if both ping and DNS lookup are failed, the WAN link will be judged as “Failed”