The topic was originally posted by Clive_A in Troubleshooting Techniques for Laymen

Background:

 

We hope this article can guide network troubleshooting, determining internal and external network issues, and offering a mind note when you troubleshoot the network when or before asking on the forum.

 

This Article Applies to:

 

All networking devices.

 

Contents:

 

1. How to determine internal(LAN) and external(WAN or ISP) network issues (via ping). Why this is important?
2. How to troubleshoot and compare test results for problem identification
3. How to identify the network storm or loop. Common symptoms.
4. How to detect WAN exit rules (using traceroute command)
5. How to use Wireshark

 

Common Techniques:

 

1. How to determine internal(LAN) and external(WAN or ISP) network issues (via ping). Why this is important?

 

Step 1, ping a device on the same LAN as the computer you are using:

• Open the Command Prompt (Windows) or Terminal (Mac/Linux) and type "ping device_IP_address -t" (e.g., "ping 192.168.0.1 -t").

We usually recommend you ping the gateway IP address to verify whether the connection from LAN > Gateway is stable or not.

• If the device is on the same LAN and the connection is stable, you should see a response with a low latency (usually around 1-2 ms). 

 

Step 2, ping a device on the external network (WAN or ISP):

• Type "ping device_IP_address -t" (e.g., "ping 8.8.8.8 -t") and press Enter.
• If there is no loss, it represents your network is quite stable and LAN > WAN is stable. LAN > Gateway is stable as well.

 

This is important because it can allow you to quickly focus troubleshooting efforts on the either internal(LAN) or external(WAN/ISP) network. It also helps to isolate the source of the problem, which can reduce the time and effort required to resolve the issue.

If it is a WAN problem, you should check with your ISP or the WAN line. Likewise, if it is LAN, you should focus on the energy on the LAN parameters or physical connections/hardware.

 

2. How to troubleshoot and compare test results for problem identification

 

Commonly, you should bear these in mind. This not only helps you resolve the issue timely without back-and-forth messages but also makes it easier for us to locate and report or fix the issue for you.

1. Eliminate common causes: Restart networking equipment (routers/switches). Test with alternative cables. Disable unnecessary services/applications consuming bandwidth or might have an impact on the test results. Remove any recently added hardware/software that could be causing conflicts.
2. Update firmware from our official website. This might fix some problems you are experiencing. Also, make sure your device's driver is up-to-date.
3. Recall if there are any changes made to your system before an issue starts. Identify the pattern of the problem and look for commonalities in each test. Compare the results if you indeed make a change. If there is something abnormal, you should bring this up so we can quickly locate if this is a firmware issue or not.
4. Isolate the problem and monitor if this only happens to a single piece of equipment or device and record its behavior. And give patterns or information about the issue later on when you post a new thread or look for the related solution.

 

3. How to identify the network storm or loop. Common symptoms.

 

Network storms, also known as network floods or traffic storms, refer to a situation where a network is overwhelmed by a large amount of traffic, leading to degraded performance or even complete failure.

Usually, your computer will lose Internet or become extremely slow with overloaded CPU usage if you take a look at the Task Manager.

 

Use filter eth[0] & 1, you might see tons of mDNS or ARP when it is experiencing the network storm. This will flood into your network and eventually cause a shutdown. When you run a ping, you would like to see a surge in the ping response time and timeout eventually.

 

(There is also a surge in the Packet percentage on the Wirehskar page(down right on the capturing page). It will increase quickly to 80-90% and slowly close to a higher percentage.)

 

4. How to detect WAN exit rules (using traceroute command)

 

Tracert (short for "Trace Route") is a network diagnostic command-line tool used to trace the path that an IP packet takes from your computer or device to a destination IP address. It provides information about each hop (intermediate router) along the route, including their IP addresses and response times.

 

 

You might find out your WAN IP address when you use this to identify your traffic. It would be very helpful when you want to identify your traffic under load balancing or policy routing scenarios.

 

(The first hop is my gateway. Next is forwarded to the WAN 10.24.7.253 which is my router's WAN side. So you can use this to identify based on your WAN status and IP address, which port is used. But this might vary based on your parameters.)

5. How to use Wireshark

 

When you use Wireshark, you might refer to the following guides on our official websites.

How to capture packets using Wireshark on SMB router or switch

How to Use Port Mirror to Capture Packets in the Controller

 

Common filters for newbies:

 

Filter Type	Syntax
IP Address Filter	ip.addr == IP-Address
Protocol Filter	tcp
	udp
Port Filter (TCP)	tcp.port == Port-Number
Port Filter (UDP)	udp.port == Port-Number
Source/Destination IP Filter	ip.src == Source-IP-Address
	ip.dst == Destination-IP-Address
Multiple filters	and
	or
Exclude	!(syntax)

 

Self-help and find out official troubleshooting guides: Routers > Label=Troubleshooting

If you encounter an issue, please follow the troubleshooting to check your settings. Besides, ensure your Omada Controller and Gateway are running with the latest firmware.

If the issue still exists after you try the suggestion above, please feel free to comment below or contact our support team with a detailed description of your issue and the steps you have tried.

 

 

Update Log:

 

Jan 11th, 2024:

Update the format. Optimize the order for a better reading experience.

 

Recommended Threads:

 

Troubleshooting Online Detection and Link Backup (Failover) Don't Take Effect

Troubleshooting Custom DDNS Is Not Working

Common Questions About the Load Balancing & Link Backup(Failover)

Configuration Guide How to Set Up Policy Routing

 

Feedback:

 

• If this was helpful, welcome to give us Kudos by clicking the upward triangle below.
• If there is anything unclear in this solution post, please feel free to comment below.

 

Thank you in advance for your valuable feedback!

 

------------------------------------------------------------------------------------------------

Have other off-topic issues to report? 

Welcome to > Start a New Thread < and elaborate on the issue for assistance.