DNS & Name Resolution
DNS is the phonebook every other Windows Server service depends on. Nine stops, one foundation block of the WSA Lego kit.
What you'll learn
- Hierarchy & zones — forward, reverse, primary, secondary
- AD-Integrated zones ★ — multi-master replicated via AD
- Record types — A, AAAA, CNAME, MX, PTR, SRV
- Forwarding — conditional + global
- Dynamic updates & scavenging — DDNS + stale-record cleanup
DNS Fundamentals
DNS (Domain Name System) translates human-readable names to IP addresses. The right-side diagram shows recursive resolution walking from your client all the way to the authoritative server.
Key Concepts
- FQDN - Fully Qualified Domain Name (e.g., dc01.hexworth.local)
- Zone - A portion of the DNS namespace managed by a server
- Record - An entry mapping a name to data (IP, alias, mail server)
- TTL - Time To Live, how long to cache a record
DNS Hierarchy
DNS uses a tree structure with the root at the top:
. (Root)
│
┌───────────┼───────────┐
│ │ │
com org local
│ │
google hexworth
│ │
www dc01
Domain Levels
| Level | Example | Description |
|---|---|---|
| Root | . (dot) | Top of hierarchy, 13 root server clusters worldwide |
| TLD | .com, .org, .local | Top-Level Domain, managed by registries |
| Second-Level | hexworth.local | Your organization's domain |
| Subdomain | dc01.hexworth.local | Hosts and child domains |
DNS Zone Types
Primary Zone
- Read/write copy of zone data
- Only one primary per zone
- Source for zone transfers
- Can be AD-integrated
Secondary Zone
- Read-only copy of zone data
- Multiple secondaries allowed
- Provides redundancy
- Gets data via zone transfer
AD-Integrated Zones
Zone data lives in AD: multi-master, replicates with AD, secure dynamic updates. Default choice for AD environments.
Forward & Reverse Lookup
Forward Lookup Zone
Name → IP Address
- Most common lookup type
- Users and apps use this
- Contains A, AAAA, CNAME records
Reverse Lookup Zone
IP Address → Name
- Used for logging, security
- Email spam checking
- Contains PTR records
DNS Record Types
Each record maps a name (or address) to data. The right panel lists every common type with examples.
| Type | Example | |
|---|---|---|
| A IPv4 | dc01 → 192.168.1.10 | |
| AAAA IPv6 | dc01 → 2001:db8::1 | |
| CNAME alias | mail → exchange01.hexworth.local | |
| MX | Mail exchanger for domain | hexworth.local → mail.hexworth.local (priority 10) |
DNS Record Types (cont.)
| Type | Purpose | Example |
|---|---|---|
| PTR | Reverse lookup (IP to name) | 10.1.168.192 → dc01.hexworth.local |
| SRV | Service location | _ldap._tcp → dc01.hexworth.local:389 |
| NS | Name server for zone | hexworth.local → dc01.hexworth.local |
| SOA | Start of Authority (zone info) | Serial, refresh, retry, expire, TTL |
SRV Records & Active Directory
AD uses SRV records for service discovery — clients query _service._protocol.domain, get host+port back.
nslookup -type=srv _ldap._tcp.dc._msdcs.hexworth.local.
DNS Forwarding
Forwarders send queries upstream instead of using root hints.
Standard
- ALL external queries
- ISP or public DNS (8.8.8.8)
Conditional
- Specific domains only
- Essential for AD trusts
Dynamic DNS Updates
Dynamic updates allow clients to automatically register their DNS records:
| Setting | Description | When to Use |
|---|---|---|
| None | No dynamic updates allowed | Static-only environments |
| Nonsecure and Secure | Any client can register | Non-AD environments only |
| Secure Only | Only authenticated clients | Recommended for AD |
How It Works
- Client boots and gets IP from DHCP
- Client sends dynamic update to DNS server
- DNS server authenticates client (if secure)
- A record created/updated for client
- DHCP can also register PTR records
Lock down the zone so only authenticated AD clients can register records.
DNS Troubleshooting
Three command-line tools cover most DNS triage. The right-side terminal walks through the typical sequence.
The triage triad
Resolve-DnsName— PowerShell-native query with object outputResolve-DnsName -Server <ip>— force a specific resolver (bypass local)Clear-DnsClientCache·ipconfig /flushdns— wipe the local cache when answers go stale
Essential Commands
Resolve a hostname to its IP address using the default DNS server.
Cache Management + Common Issues
Flush + inspect DNS caches.
Issues: stale records (enable scavenging) · missing SRV (nltest /dsregdns) · wrong DNS server · forwarder timeout.
DNS Scavenging
Scavenging automatically removes stale (old) DNS records that are no longer valid.
Why Scavenging Matters
- DHCP clients may get new IPs but old records remain
- Decommissioned servers leave orphaned records
- Stale records cause failed connections
- Zone becomes cluttered and hard to manage
Configuration
Turn on automatic scavenging at the server level with a 7-day interval.
Why Scavenging Matters (cont.)
Enable aging on the specific zone so stale records get timestamped.
Module Summary
Key Takeaways
- DNS is hierarchical - root → TLD → domain → hostname
- AD-integrated zones provide security and replication
- SRV records are critical for Active Directory
- Forwarders handle external resolution
- Secure dynamic updates prevent unauthorized registrations
PowerShell Quick Reference
List every DNS zone hosted on the server to see what is configured.
Listing and Testing
View all DNS records within a specific zone to audit its contents.