Network Communication Failure and Troubleshooting Guide

In today’s networked environments, reliable connectivity is crucial for seamless communication and data sharing. However, various issues can lead to Network Communication Failure, impacting both network performance and user productivity. This guide covers common causes and solutions for network communication problems, from managed switch configurations and limited port availability to resource sharing errors and IP address conflicts. Understanding these issues and their resolutions helps maintain a stable network and minimize downtime.

1. Network communication Failure when the switch is powered on

【Failure phenomenon】

Network communication failure occurs when devices cannot connect properly upon startup. Network Communication Failure may cause delays and slowdowns in accessing networked computers, requiring attention to resolve network loops and other related issues effectively.

【Failure Analysis】

Since this switch is a managed switch, in order to avoid topological loops in the network, which may lead to network paralysis, the managed switch enables the spanning tree protocol by default. In this way, even if there is a loop in the network, only one path will be retained, and other links will be automatically cut off. Therefore, when the switch is powered on, each port needs to enter the monitoring, learning and forwarding states in turn, and this process takes about 3 to 5 minutes.

If you need to start the switch quickly, you can start “PortFast” on the port directly connected to the computer, so that the port will be immediately and permanently switched to the forwarding state. In this way, the device can be connected to the network immediately, avoiding the waiting time required for the port to transition from the listening and learning state to the forwarding state.

【Troubleshooting】

If you need to quickly forward data after the switch is powered on, you can disable the Spanning Tree Protocol or set the port to PortFast mode. However, it should be noted that although these two methods omit the port detection process, once a topology loop is generated between network devices, network communication will be paralyzed.

2. Fault 2: Only 4 ports of a 5-port switch can be used

【Failure phenomenon】

The office setup includes four computers but only one network socket, so a 5-port switch with one designated UpLink port was chosen. Initially, the plan was to connect each of the four computers to the switch’s four available ports, reserving the UpLink port to link to the LAN. However, upon connection, Network Communication Failure occurred, preventing normal operation on port 1, which is adjacent to the UpLink port.

【Failure Analysis】

The UpLink port cannot be considered as a separate port because it is actually the same port as the adjacent port, but it is used to connect different objects. With the UpLink port, a hub device can be connected to a normal port of another hub device using a straight-through cable, eliminating the need for a crossover cable.

The chips of switches and hubs are usually ×4, so the ports of hub devices are mostly 4-port, 8-port, 16-port, 24-port, etc. If it is made into 5-port, 3 modules will be wasted, thus increasing the cost.

【Troubleshooting】

Replacing the 4-port switch with an 8-port switch can solve the problem.

3. Network Communication Failure in Server Resource Sharing

3.1 Unable to assign access rights to users:

【Failure phenomenon】

The network operates within a Windows domain, with clients running Windows 2000 Professional. The server is assigned an IP of 192.168.0.1, DNS is set to 127.0.0.1, and the router’s internal IP matches the server at 192.168.0.1. All clients automatically acquire IP addresses and are part of the DomainUser group. However, when configuring shared files on the server, Network Communication Failure arises, as specified permissions are set but access remains restricted.

【Failure Analysis】

In Windows domain, NTFS permissions and share permissions are used to set access rights for shared folders. However, NTFS permissions are higher than share folder permissions, which means that you must first set NTFS permissions for the folder you want to share, and then set share folder permissions for it. If there is a conflict between the two, the NTFS permissions will prevail.

【Troubleshooting】

First, specify NTFS permissions for users, and then specify shared folder permissions. For example, if you need to create a shared folder TESTA for user A, so that the shared folder can be fully controlled by user A and accessed by any other user, you must first set the access rights of TESTA, specify “full control” permissions for user A, and set “read-only” permissions for Everyone. Similarly, you should also set the permissions for shared folders in the same way.

3.2 Shared folders cannot be displayed in “My Network Places”

【Failure phenomenon】

Some folders have been shared, but cannot be viewed in “My Network Places”, but some shared files on the same computer can be seen.

【Failure Analysis】

Since some shared folders can be seen, it means that the network configuration and connection of the computer are basically normal. And this is not a fault, but a configuration type of sharing properties. In Windows system, there are two main types of shared files, one is for system call; the other is for other users to access. Shared files for system call do not appear in “My Network Places”, but can be displayed by commands such as “Net View”; shared files for other users to access can be seen in “My Network Places”.

So how do you configure an invisible shared folder? Just add a dollar sign “$” after the shared folder name. For example, in Windows Server 2003, the folder automatically created for each user is such a shared folder. Each user can only see his own user folder, but cannot see other people’s user folders. There are also some disks that are shared in Windows Server 2003 after installation, but their shared file names all have a “$” sign after them, so client users cannot see them.

【Troubleshooting】

Delete the “$” sign after the shared file name, and the shared file that cannot be displayed will appear in “My Network Places”.

4. Hub and router cannot share Internet access

【Failure phenomenon】

Multiple computers use broadband routers and hubs to share the Internet through the hub expansion port. After the connection is completed, the three machines directly connected to the broadband router LAN port can access the Internet, but the computer connected through the hub cannot access the Internet. Whether the router and the hub are connected by a crossover cable or a parallel cable, it does not work, and the light on the hub connected to the router LAN port is not on. In addition, the computer on the hub cannot ping the router or other computers. What is the reason?

【Failure Analysis】

1. Hub itself is faulty

The fault phenomenon is that the computers on the hub cannot ping each other, let alone the router. This fault can only affect all computers connected to the hub.

2. Cascading failures

For example, the cascade jumper between the router and the hub uses an incorrect line sequence, or the jumper connectivity is faulty, or an incorrect cascade port is used. The fault phenomenon is that the computers on the hub can ping each other, but the router cannot be pinged. However, the Internet access of the computer directly connected to the router LAN port will not be affected.

3. Broadband router failure

If it is a LAN port failure, the result will be similar to a cascading failure: if it is a routing failure, the result will be that no computer within the network can access the Internet, whether connected to the router’s LAN port or to the router.

【Troubleshooting】

From the fault phenomenon, the computer connected to the hub can neither ping the router nor other computers. It is preliminarily determined that there is a connection failure between the computer and the hub. At this time, you can try to replace a network cable. If the fault still cannot be eliminated, you can replace the hub to solve it.

5. Network Communication Failure Due to IP Address Conflicts

【Failure phenomenon】

All machines have unique IP addresses in the network. There are always two machines that have an address conflict with an IP address and a string of addresses when they are started. The problem persists after changing the IP address. And when there is a conflict, only one machine can access the Internet.

【Failure Analysis】

I carefully looked at the conflict prompt, which was a string of addresses. Could it be a physical address conflict, that is, a MAC address conflict? But I couldn’t search each machine one by one. I used IPbook Super Network Neighborhood to scan the entire network segment, and found that the MAC addresses of the network cards of the two machines were exactly the same.

Troubleshooting

Replace the network card. After replacing the network card, the problem is solved. All network devices working in the network, including network cards, switches, and routers, have a physical address called a MAC address. The MAC address contains the manufacturer of the network device and a unique serial number in the global network device. All network data exchanges are based on MAC address exchanges, not IP address exchanges. Therefore, if there is a MAC address conflict and the IP address does not conflict, it will also cause network interruption because the data cannot find the end point. Therefore, when buying a network card, you must buy a genuine product and don’t buy a defective product for the sake of cheapness. If it is a network card MAC address conflict, it is still a small matter to replace one. If the switch has a MAC address conflict, then you will be in big trouble.

6. Summarize

In conclusion, addressing Network Communication Failure requires a thorough understanding of network protocols, configurations, and equipment compatibility. By following best practices—such as enabling PortFast on switches, correctly configuring permissions for shared resources, and ensuring unique MAC addresses—network reliability and performance can be significantly improved. Taking proactive steps to resolve these issues helps create a more efficient and accessible network environment for all users.