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A computer is assigned an IP address of 169.254.33.16. What can be said about the computer, based on the assigned address?

A computer is assigned an IP address of 169.254.33.16. What can be said about the computer, based on the assigned address?

  • It can communicate with networks inside a particular company with subnets.
  • It can communicate on the local network as well as on the Internet.
  • It has a public IP address that has been translated to a private IP address.
  • It cannot communicate outside its own network.

The correct answer is:

“It cannot communicate outside its own network.”

Explanation:

The IP address assigned to the computer, 169.254.33.16, belongs to a specific range of addresses known as the Link-Local Address Range. This range, from 169.254.0.0 to 169.254.255.255, is defined by the Internet Assigned Numbers Authority (IANA) for use in automatic private IP addressing (APIPA). The primary purpose of APIPA is to provide an IP address to a device when it cannot obtain one through a standard process, like through a DHCP (Dynamic Host Configuration Protocol) server.

What is an APIPA Address?

APIPA (Automatic Private IP Addressing) addresses are a subset of private IP addresses designed to facilitate local network connectivity in the absence of a DHCP server or when DHCP services are temporarily unavailable. The address range 169.254.0.0/16 has a subnet mask of 255.255.0.0, which means it covers addresses from 169.254.0.1 to 169.254.255.254. Devices configured with APIPA addresses are intended to communicate only within the local subnet or local network they are physically connected to. As a result, an APIPA-assigned IP address does not enable communication outside the immediate local network.

When Does a Computer Get an APIPA Address?

A computer is assigned an IP address in the 169.254.x.x range under the following circumstances:

  1. DHCP Server is Unreachable or Unavailable: When a computer or device is set to automatically receive an IP address (i.e., it is configured to use DHCP) but cannot connect to a DHCP server, it will assign itself an address from the 169.254.x.x range.
  2. Network Connectivity Issue: There could be issues with physical or network connectivity. For example, a disconnected Ethernet cable, faulty network switch, or incorrectly configured Wi-Fi settings might prevent the device from reaching the DHCP server.
  3. Configuration Problem: The DHCP server may be improperly configured or may have run out of addresses in its pool, causing devices on the network to fail in acquiring valid IP addresses.

When a computer receives an address from this range, it generally indicates that it cannot connect to the larger network infrastructure, like routers or gateways, that would provide access to other subnets or the Internet.

Characteristics and Limitations of Link-Local (APIPA) Addresses

  1. Local Network Only: A device with an APIPA address can only communicate with other devices on the same subnet that also have an APIPA address. In other words, the device can interact only within the local network and cannot access external networks, such as the Internet or other subnets.
  2. Non-Routable: APIPA addresses are non-routable. Routers, by design, do not forward packets from these addresses, making it impossible for the device to connect to devices outside of the local network.
  3. Temporary Measure: APIPA is typically a temporary solution. It is used by systems to establish local communication until the DHCP server becomes available again, at which point the device will request and, if successful, receive a valid IP address for broader network communication.
  4. No Communication Outside Local Network: Since APIPA addresses are non-routable, any services that rely on Internet or WAN access will not be available to devices with these addresses.

Why the Other Options are Incorrect

  1. “It can communicate with networks inside a particular company with subnets.”
    • This statement is incorrect because a device with an APIPA address (169.254.x.x) is limited to communicating within its local subnet only. APIPA addresses are not routable, which means they cannot be forwarded by routers or communicate with other subnets, even if they belong to the same company network. This restriction means that APIPA addresses only work within the local network segment or subnet that the device is directly connected to.
  2. “It can communicate on the local network as well as on the Internet.”
    • This statement is also incorrect. A device with an APIPA address cannot access the Internet because APIPA addresses are non-routable and are designed solely for local network communication. Devices with 169.254.x.x addresses can communicate with each other on the same local network segment, but they are effectively isolated from external networks, including the Internet.
  3. “It has a public IP address that has been translated to a private IP address.”
    • This is also incorrect. An APIPA address is inherently a private address and is not related to any public IP address. There is no network address translation (NAT) or conversion taking place in this scenario. Instead, the device assigns itself a 169.254.x.x address due to the lack of DHCP server connectivity or configuration. The purpose of APIPA is not to translate or link public and private IPs but to allow limited communication within a local network.

Use Cases and Practical Scenarios of APIPA Addresses

While APIPA addresses are usually seen as a fallback mechanism, they do have practical applications:

  1. Simple Peer-to-Peer Networking: APIPA allows computers to establish a local network without the need for a DHCP server. This feature can be useful in settings where users need to set up a small network without the complexities of network administration, such as for quick file sharing or printing within a small group of devices.
  2. Network Troubleshooting: If a computer displays an APIPA address, it often signals to network administrators that there might be a problem with the DHCP server or with connectivity to the server. By identifying APIPA addresses, technicians can troubleshoot and isolate network issues more quickly, focusing on DHCP-related configurations or connectivity issues.
  3. Limited Local Connectivity: In cases where only local network resources are needed, APIPA addresses can still allow limited functionality, such as sharing local files, printing, or accessing devices within the same subnet. However, this functionality is minimal and lacks the ability to connect to external networks or services.

How APIPA Impacts Network Performance and User Experience

While APIPA provides a valuable fallback mechanism, relying on APIPA addresses can lead to a suboptimal user experience, especially in environments where external network connectivity is essential. Users with APIPA-assigned devices may find themselves isolated from essential network resources, such as web applications, databases, or cloud services. In enterprise settings, APIPA can disrupt workflow and productivity, as it may prevent users from accessing necessary resources hosted on other subnets or in the cloud.

How to Resolve an APIPA Address Issue

  1. Verify DHCP Server Availability: Network administrators should check if the DHCP server is functioning properly. They can inspect server logs, check for IP pool availability, and verify network connectivity between devices and the DHCP server.
  2. Check Network Connectivity: Physical connections, such as Ethernet cables, switches, and Wi-Fi configurations, should be tested to ensure devices can connect to the network and reach the DHCP server.
  3. Reboot or Reconnect the Device: In some cases, restarting the device or disconnecting and reconnecting to the network can trigger a new DHCP request, allowing the device to obtain a valid IP address.
  4. Configure Static IP (If Appropriate): For environments that rely on consistent local network connectivity, manually assigning static IP addresses within the correct private IP range (such as 192.168.x.x or 10.x.x.x) can prevent the device from needing to rely on DHCP.

Conclusion

A computer assigned an IP address of 169.254.33.16 has received an APIPA address due to the lack of a DHCP response. This assignment restricts it to local network communication only, meaning it cannot communicate outside its own network. The APIPA range is a valuable tool for maintaining minimal connectivity within a local subnet, but it lacks broader network communication capabilities, making it unsuitable for accessing the Internet or other network subnets.