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If you recall a normal DNS query works like this:
- A DNS client queries a recursive DNS server.
- The server caches the result.
- Next time the DNS server will be able to respond more quickly to other DNS clients querying the same information.
- The amount of time that a record resides in cache is determined by the Time to Live (TTL) value of the record.
- If the TTL, is set to a shorter time or percentage a record could be overwritten if more recent data is available for the record.
- However, this exposes a security issue. A malicious person may try to overwrite the record and redirect clients to an unsafe Web site.
To mitigate this risk in Windows server 2016:
- You can use DNS cache locking to determine when information in the DNS cache can be overwritten.
- When you enable cache locking the DNS server does not allow updates until the TTL has fully expired.
- By default, the TTL is set to 100% or 24 hours.
To configure Cache Locking we need to open up PowerShell in administrator mode.
I’ll show you two ways to accomplish setting your TTL percentage. First to check the current percentage
Get-Dnsserver
If we Drop down to the ServerCache heading we notice that the locking percent by default is set to 100%. If you want to change the percentage type to 70% type
Set-DnsServerCache –LockingPercent 70
You can also use the dnscmd to accomplish this.
- You can check the current TTL setting by typing the command dnscmd /info /cachelockingpercent
- In most environments you are not going to adjust this, but if you want to reduce the time that a record in your cache can get overwritten, you can do so by running the following commands:
dnscmd /config /cachelockingpercent 100 (24 hours)
dnscmd /config /cachelockingpercent 75 (18 hours)
dnscmd /config /cachelockingpercent 50 (12 hours)
dnscmd /config /cachelockingpercent 0 (Update immediately)
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CURRICULUM
Course Introduction • 10min
0 / 2 lessons complete
Instructor and Course Introduction
Video | 7 min
What's New in Windows Server 2016 DNS
Free lesson
Video | 3 min
DNS Basics • 56min
0 / 8 lessons complete
What is DNS
Video | 3 min
Installing the DNS Windows Server Role
Video | 6 min
Building DNS Server Quiz
Quiz | 10 Questions
The Hosts File
Video | 4 min
DNS Console Overview
Video | 7 min
Recursive and Iterative Queries
Video | 8 min
DNS Basics LAB
Video | 10 min
DNS Basics Quiz
Quiz | 8 Questions
DNS Resource Records • 45min
0 / 5 lessons complete
DNS Resource Record Types
Video | 3 min
Creating the mytestzone Forward Lookup Zone
Text | 2 min
Creating DNS Resource Records
Video | 4 min
Creating DNS Resource Records Lab
Lab | 30 min
DNS Resource Records Quiz
Quiz | 7 Questions
DNS Zones • 4hr 11min
0 / 12 lessons complete
DNS Zones
Video | 4 min
Creating a Forward and Reverse Lookup Zone
Video | 5 min
Creating a Secondary Zones
Video | 9 min
Stub Zone Creation
Video | 11 min
Active Directory Zone Replication
Video | 12 min
Implementing DNS Forwarding
Video | 8 min
Implementing Conditional DNS Forwarding
Video | 7 min
Forward and Reverse Zone Creation Lab
Lab | 60 min
Creating a Secondary Zone Lab
Lab | 30 min
Conditional Forwarding Lab
Lab | 60 min
Creating a Stub Zone Lab
Lab | 30 min
DNS Zones Quiz
Quiz | 15 Questions
DNS Delegation • 50min
0 / 4 lessons complete
Domain Name System and DNS Delegation
Video | 7 min
Windows 2016 Server and DNS Zone Delegation
Video | 8 min
DNS Delegation Lab
Lab | 30 min
QUIZ - Domain Name System and DNS Delegation
Quiz | 5 Questions
DNS Security Techniques • 36min
0 / 5 lessons complete
DNS Security Techniques Overview
Video | 9 min
Configuring DNS Cache Locking
Video | 5 min
Configuring DNS Socket Pools
Video | 6 min
Configuring Response Rate Limiting
Video | 8 min
DNS Security Techniques Quiz
Quiz | 8 Questions
Advanced DNS Topics • 22min
0 / 5 lessons complete
Overview of Advanced Topics
Video | 1 min
Enabling Round Robin and Netmask Ordering
Video | 5 min
Configuring Recursion
Video | 4 min
IPV4 and IPV6 Root HInts
Video | 6 min
Advanced DNS Topics Quiz
Quiz | 6 Questions
DNS Security (DNSSEC) • 1hr 16min
0 / 6 lessons complete
Windows DNS Security Overview
Video | 7 min
Symmetric vs Asymmetric Encryption
Video | 5 min
Installing DNSSEC on Windows 2016 Server
Video | 12 min
DNSSEC Client Install
Video | 7 min
DNSSEC (DNS Security Lab)
Lab | 30 min
DNSSEC Quiz
Quiz | 15 Questions
DNS Policies • 55min
0 / 6 lessons complete
DNS Policies Background Information
Video | 8 min
Configuring DNS Filtering
Video | 7 min
Configuring Split Brain DNS in an Active Directory Environment
Video | 12 min
Configuring DNS Selective Recursion Policy
Video | 7 min
Configuring a Traffic Management Policy
Video | 11 min
DNS Policies Quiz
Quiz | 10 Questions
PowerShell for DNS • 1hr 27min
0 / 6 lessons complete
PowerShell for DNS Part 1
Video | 2 min
PowerShell for DNS Part 2
Video | 5 min
PowerShell for DNS Part 3
Video | 10 min
PowerShell for DNS Part 4
Video | 5 min
PowerShell for DNS LAB
Lab | 60 min
Powershell for DNS Quiz
Quiz | 5 Questions
Troubleshooting DNS Issues - Troubleshooting Tools • 1hr 39min
0 / 8 lessons complete
Troubleshooting Tools Every IT Pro Must Know
Video | 9 min
The Events Viewer Overview
Video | 6 min
Subscriptions
Video | 9 min
Monitoring and Debug Logging
Video | 9 min
Trouble-Shooting DNS Client Issues
Video | 4 min
Troubleshooting Subscriptions Lab
Lab | 30 min
DNS Troubleshooting Lab
Lab | 30 min
DNS Troubleshooting Quiz
Quiz | 2 Questions