Following a recent core switch update, enterprise workstations connected to VLAN 30 (10.30… — CompTIA Network+

Following a recent core switch update, enterprise workstations connected to VLAN 30 ( $10.30.0.0/24$ ) fail to communicate outside their local subnet. Preliminary reports indicate workstations are assigning themselves addresses in the range $169.254.0.0/16$ . Place the following diagnostic and remediation steps in the correct chronological sequence to isolate and resolve this DHCP assignment failure according to standard network troubleshooting methodology.

1Inspect the client workstation network stack configuration using `ipconfig /all` to confirm an APIPA address allocation and identify missing default gateway settings.
2Inspect the VLAN 30 switch virtual interface (SVI) configuration on the Layer 3 switch to verify the presence and syntax of the `ip helper-address` entry.
3Verify intermediate firewall and Access Control List (ACL) configurations between the relay agent and the DHCP server to ensure UDP ports 67 and 68 are unblocked.
4Check the central DHCP server console for VLAN 30 to confirm scope activation, exclusion ranges, and IP address pool availability.
5Execute `ipconfig /release` followed by `ipconfig /renew` on the client workstation to verify successful lease acquisition and gateway assignment.

Answer

The correct sequence starts with verifying the client's APIPA state, followed by checking the local gateway's DHCP relay helper address, auditing intermediate firewall filtering rules for UDP ports 67/68, inspecting DHCP server scope statistics, and finally renewing the client IP lease.

The correct troubleshooting sequence follows the standard CompTIA troubleshooting framework, moving logically from host symptom verification to local gateway relay inspection, intermediate network path filter checks, backend server scope verification, and final client validation.

Step-by-Step Solution

Inspect client network configuration using `ipconfig /all`.

Confirms host has an Automatic Private IP Addressing (

169.254.x.x

) address, indicating DHCPDISCOVER requests timed out.

Establishing the baseline symptom on the local host isolates the scope of the problem to IP address auto-configuration failure.

Check the VLAN 30 interface configuration on the default gateway switch.

Verifies whether the `ip helper-address` directive is properly configured to forward DHCP broadcasts across subnet boundaries as unicast packets.

Since clients reside on a separate subnet from the central DHCP server, missing relay configuration is the most common cause of multi-VLAN DHCP failure.

Audit ACLs and security rules along the path between relay agent and DHCP server.

Ensures that unicast DHCP requests (UDP port 67) and responses (UDP port 68) are permitted through network firewalls.

Even with a valid helper address, network transport controls can drop unicast relay packets before reaching the server.

Examine the DHCP server scope statistics for

10.30.0.0/24

Determines if the IP address pool has been exhausted or if the scope is deactivated.

If the relay agent successfully reaches the server, the server must have an active pool with unassigned addresses to grant a lease.

Re-issue a DHCP request on the client via `ipconfig /renew`.

Confirms the host acquires a valid

10.30.0.0/24

IP address, subnet mask, default gateway, and DNS servers.

Verifying functionality directly on the affected host ensures the issue is fully remediated and tests the complete end-to-end lease acquisition process.

Key Concept

Troubleshooting DHCP Relay and IP Addressing Services across Subnets

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