Fault 1: Unable to obtain IP address

Symptom: The network does not appear to be available. The operating system may warn that it is unable to obtain an IP address from the DHCP server. After checking the network card, I did not get an IP address.

the reason:

1. The DHCP server may lack the available IP address.

2. The server's DHCP service may be down.

3. The terminal device uses a static IP address instead of automatically obtaining an IP address.

4. The DHCP request of the terminal device is not transmitted to the server. This problem often occurs when configuring a new device for a VLAN. At this time, no VLAN is set to forward the DHCP request to the DHCP server.

Solution:

The key issue is that this type of failure is limited to one user or multiple users. If only one user is affected, check the NIC settings to make sure it uses the DHCP service. Next, check the switch and look at the ports and VLANs to see if VLAN members are configured. Check if other devices on this VLAN can obtain an IP address. If these devices are unable to obtain an address, the problem may be caused by the router not forwarding the DHCP request to the DHCP server. If multiple devices on multiple subnets have this problem, the problem may be caused by the server itself. The server may not be running the DHCP service, or it may not have enough IP addresses to allocate.

Fault 2: DNS problem

Symptom: Users cannot access the Internet or critical applications. The network seems to have been "smashed".

Reason: It may be the reason for DNS. The client computer cannot resolve the server's name with the IP address of the accessed server, so it will not be able to send connection requests. This is usually due to a misconfiguration of the DNS server on the client. When the client sends a DNS request, the DNS server cannot find the record in the database or a packet loss occurs. DNS is a UDP-based protocol, so lost packets cannot be forwarded, causing DNS failures.

Solution:

Check the client's configuration to see what DNS server it is using. If the server is misconfigured, adjust this setting in the client or in the DHCP server. Tests are repeated over the client connection to determine if the response is delayed due to packet loss.

If the packet is lost, you should look for an Ethernet error between the client and the server. Capture failed DNS requests and decide whether there is a response from the server based on the information obtained. Ideally, managers can set up a tool that can continuously test DNS servers, which can warn you when problems occur.

Here, we only look at two common network problems that technicians may encounter. In many cases, the scope of the fault can be further reduced and further resolved. In addition, the right tools are used to help isolate and resolve problems quickly and to improve network performance in the shortest possible time.