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A technician troubleshooting a network problem has used CLI commands to determine that a computer has not been allocated a correct IP address from the DHCP server. Which command can the technician use to solve this problem?

A technician troubleshooting a network problem has used CLI commands to determine that a computer has not been allocated a correct IP address from the DHCP server. Which command can the technician use to solve this problem?

  • ping
  • ipconfig /release
  • tracert
  • ipconfig /renew

The correct answer is ipconfig /renew. This command is used by a technician to solve the problem where a computer has not been allocated a correct IP address from the DHCP server. It forces the computer to request a new IP address from the DHCP server, potentially resolving issues related to improper IP allocation.

Let’s explore in detail how the ipconfig /renew command works, why it’s used, and how it fits into the troubleshooting process, especially in relation to DHCP-related network problems.

Understanding the DHCP Process

Dynamic Host Configuration Protocol (DHCP) is a network management protocol that automatically assigns IP addresses and other essential network settings (such as subnet mask, default gateway, and DNS servers) to devices on a network. When a device connects to a network, it acts as a DHCP client, requesting an IP address from a DHCP server.

Here’s a brief overview of the DHCP process:

  1. DHCP Discover: The client sends a broadcast message requesting an IP address.
  2. DHCP Offer: The DHCP server responds with an available IP address.
  3. DHCP Request: The client requests to lease the offered IP address.
  4. DHCP Acknowledge: The server acknowledges the lease and assigns the IP address to the client.

If the DHCP process fails or if the computer is unable to obtain a proper IP address, it can result in network connectivity issues. A common symptom of this problem is that the device receives an Automatic Private IP Address (APIPA) (usually in the range 169.254.x.x), which prevents it from communicating with other devices on the network.

Troubleshooting DHCP-Related IP Allocation Problems

When troubleshooting a network problem where a computer has not been allocated a correct IP address, a technician can use various Command Line Interface (CLI) commands to diagnose and solve the issue. The most common issue is that the computer either has not received an IP address from the DHCP server or has an incorrect or outdated IP address.

To address this problem, the ipconfig /renew command is particularly useful. This command forces the DHCP client on the computer to send a new request to the DHCP server, asking for a fresh IP address. The server then assigns a new address if one is available, along with the relevant network configuration settings.

How to Use the ipconfig /renew Command

To run the ipconfig /renew command, follow these steps:

  1. Open the Command Prompt:
    • In Windows, press Windows + R, type cmd, and press Enter.
  2. Enter the command:
    • Type ipconfig /renew and press Enter.

The command will send a request to the DHCP server for a new IP address. If the computer is able to communicate with the DHCP server, the server will respond by assigning a new IP address to the computer.

Why the ipconfig /renew Command is Effective

  1. Forces a New DHCP Lease: Sometimes, a computer may hold on to an old or invalid IP address, preventing proper network communication. By using ipconfig /renew, the device releases its current IP address and requests a new one from the DHCP server, ensuring it gets a valid IP address.
  2. Resolves APIPA Issues: When a computer is unable to contact the DHCP server, it may automatically assign itself an APIPA address in the 169.254.x.x range. This is a clear indication that something is wrong with the DHCP process. Running ipconfig /renew will attempt to obtain a correct IP address from the DHCP server, resolving the issue.
  3. Dynamic Networks: In networks where devices frequently join and leave, DHCP is essential for dynamically assigning IP addresses. The ipconfig /renew command helps ensure that devices get updated IP addresses and configurations, particularly when there are changes in the network infrastructure, such as a new router or DHCP server.

Example Scenario

Let’s consider an example where a technician is troubleshooting a network issue:

  • The user reports that they cannot access the internet or the company’s internal network.
  • The technician checks the IP address using the ipconfig command and sees that the computer has an APIPA address (169.254.x.x).
  • This suggests that the computer was unable to contact the DHCP server to obtain a valid IP address.

At this point, the technician can use the ipconfig /renew command to attempt to obtain a new IP address from the DHCP server. Here’s how the process works:

  1. The command forces the computer to release its current IP address (if any) and sends a new DHCP request.
  2. The DHCP server responds by offering an available IP address along with other necessary network configurations (such as DNS servers and gateway settings).
  3. The computer then applies this new IP address, allowing it to communicate with the network and regain access to resources like the internet or internal servers.

If the ipconfig /renew command succeeds, the technician can verify that the computer now has a valid IP address (e.g., 192.168.1.x or 10.0.0.x, depending on the network). The user should be able to access the network resources and the internet without further issues.

When to Use Other Commands

In troubleshooting, various CLI commands are useful for different scenarios. Here’s how the other commands mentioned in the options compare to ipconfig /renew:

  1. Ping: The ping command is used to test connectivity between the client computer and another device (such as a router or server) by sending ICMP echo requests. While useful for diagnosing connectivity issues, it does not help in renewing the IP address from the DHCP server.
  2. Ipconfig /release: This command is used to release the current DHCP lease, meaning it tells the computer to give up its current IP address. It is often used in combination with ipconfig /renew. For example, a technician might first use ipconfig /release to force the computer to relinquish its current IP address, followed by ipconfig /renew to obtain a new one.
  3. Tracert: The tracert (trace route) command is used to trace the path that packets take from the client computer to a destination (such as a remote server). It’s useful for identifying where along the route a connectivity issue might be occurring, but it does not address DHCP-related problems or incorrect IP addresses.

Preventing DHCP Issues

To minimize future DHCP-related problems, network administrators can take the following steps:

  1. Ensure DHCP Server Availability: Verify that the DHCP server is properly configured and available to all clients on the network. This may involve checking server settings, IP address ranges, and lease durations.
  2. Configure Backup DHCP Servers: In larger networks, having multiple DHCP servers (with different scopes) can provide redundancy in case one server fails. This ensures continuous IP address assignment for devices.
  3. Check Network Connectivity: Ensure that clients can communicate with the DHCP server by verifying network cabling, switch configurations, and wireless access points.

Conclusion

The ipconfig /renew command is a powerful tool for network troubleshooting, particularly when a computer has not been allocated a correct IP address from the DHCP server. It forces the DHCP client to request a new IP address, which can resolve issues such as the assignment of an APIPA address or an outdated lease. Using this command, technicians can quickly restore proper network connectivity for users, ensuring that their devices have valid IP addresses and can communicate effectively with other devices on the network.