DNS/DHCP Operational Runbook — 2026

Purpose:
Provide step-by-step operational procedures for verifying, troubleshooting, and maintaining DNS and DHCP services used in the lab environment.

Objective:
Maintain a repeatable DNS/DHCP support workflow that separates endpoint configuration issues, resolver failures, DHCP scope problems, and upstream routing or firewall symptoms.

Technical areas:
- Windows DNS and DHCP service review.
- Linux DNS resolver and DHCP service concepts.
- Active Directory name resolution checks when domain services are in scope.
- DHCP scope, reservation, option, and lease validation.
- Change documentation, rollback preparation, and evidence capture.

Routine checks:
- Verify DNS service is running on authoritative servers: `systemctl status named` or check Windows DNS service.
- Confirm DHCP scope utilization and active leases; export leases for change audits.
- Confirm endpoint DNS server assignment before changing resolver settings.
- Confirm gateway and DNS options match the intended VLAN or network segment.

Common tasks:
1. Verify DNS zone integrity and replication. On Windows: `repadmin /showrepl` and check DNS event logs.
2. Check DHCP scope settings: address range, exclusions, reservations; document any manual reservations.
3. Restart service safely: schedule maintenance, `net stop dhcpserver && net start dhcpserver` (Windows) or restart `isc-dhcp-server` on Linux.
4. Validate client-facing DNS: `nslookup`, `dig +trace` and confirm expected A/CNAME records.
5. For DHCP reservation issues, confirm MAC address and reservation mapping; test by forcing DHCP renew on client.

Validation:
- Record the affected endpoint, source VLAN, expected scope, assigned address, gateway, DNS server, and test result.
- Validate DNS by testing internal records and external resolution separately.
- Validate DHCP by releasing/renewing a lab client lease only after recording current state.
- Record failures with remediation notes instead of replacing them with passing results.

Rollback and change notes:
- Before any change, export the current configuration and DHCP leases to the evidence store.
- If an automated change causes outage, restore the exported configuration and restart services in the correct order.

Contact and escalation:
- Owner: Jeremy Fontenot
- Escalation guidance: preserve command output, record affected scope, and use the incident runbook if the issue affects multiple systems or a security boundary.