CompTIA Network+ (N10-009)Network TroubleshootingMedium
Several new employees at a branch office report that their laptops receive IP addresses in the 169.254.0.0/16 range and cannot access any network resources. Other existing devices on the same subnet are functioning normally. What is the MOST likely cause?
- AThe DNS server is unreachable
- BThe DHCP server's scope has been exhausted
- CThe default gateway is misconfigured
- DA duplicate IP address conflict exists
Show answer & explanationAnswer & explanation
Correct answer: B. The DHCP server's scope has been exhausted
An APIPA address (169.254.x.x) is assigned by a client when it cannot reach a DHCP server, commonly because the DHCP scope has run out of available leases. Since existing devices already hold valid leases and only new devices are affected, scope exhaustion is the most likely cause.
Why the other options are wrong
- A. DNS failure would not cause an APIPA address; it would cause name resolution failures with a valid IP.
- C. A misconfigured gateway would not prevent DHCP from assigning a valid IP address.
- D. A duplicate IP conflict typically shows a conflict warning, not an APIPA address.
APIPA (Automatic Private IP Addressing)
A Windows fallback mechanism that assigns an address in the 169.254.0.0/16 range when a DHCP server cannot be reached.
- APIPA addresses cannot route beyond the local subnet
- Common causes: DHCP server down, scope exhausted, or network cable/link issue
- Devices with existing valid leases are unaffected until they need renewal
Memory trick: 169 means 'I couldn't reach the DHCP guy'