31 DNS Service Basics

Introduction to DNS Basics
- DNS (Domain Name System) is one of the most challenging services to configure.
- It maps domain names to IP addresses (forward lookup) and IP addresses to domain names (reverse lookup).
- DNS servers answer queries from client computers based on stored records.
Types of DNS Lookups
- Forward Lookup: Converts domain names into IP addresses (e.g., ncaecybergames.org → 192.168.2.1).
- Reverse Lookup: Converts IP addresses into domain names (192.168.2.1 → ncaecybergames.org).
- Both lookups require proper zone file configuration.
DNS Software Used in Mini Hack
- The bind service is commonly used to configure a DNS server.
- Configuration files for bind are typically found in /etc/bind/ (Ubuntu) or /etc/named/ (CentOS).
- The service is managed using systemctl status named to check if it’s running.
Finding and Editing DNS Configuration Files
- The primary configuration file for bind is named.conf, found in /etc/bind/.
- Additional configurations are stored in files like named.conf.options, named.conf.local, and named.conf.default-zones.
- Some settings are included from external files to allow modular configuration.
Setting Up a Forward Lookup Zone
- The forward zone maps domain names to IP addresses.
- The entry format:
```
zone "ncaecybergames.org" {  
    type master;  
    file "/etc/bind/zones/forward.ncaecybergames.org";  
};  
```
- This configuration tells the DNS server to refer to forward.ncaecybergames.org for domain mappings.
- Setting Up a Reverse Lookup Zone
- The reverse zone maps IP addresses to domain names.
- The entry format:
```
zone "8.168.192.in-addr.arpa" {  
    type master;  
    file "/etc/bind/zones/reverse.ncaecybergames.org";  
};  
```
- The IP address must be written in reverse order, following the arpa notation.
- Creating Forward and Reverse Lookup Files
- The forward lookup file contains A records, associating names with IPs:
```
www IN A 192.168.8.2  
sandbox-ubuntu IN A 192.168.8.2  
```
- The reverse lookup file contains PTR records, associating IPs with names:
```
2 IN PTR www.ncaecybergames.org.  
2 IN PTR sandbox-ubuntu.ncaecybergames.org.  
```
Applying DNS Configuration Changes
- Restart the DNS service after modifying configurations:
```
sudo systemctl restart named  
```
- Verify its status with:
```
sudo systemctl status named  
```
- Any syntax errors will prevent the service from starting.
- Testing DNS Resolution
- Use nslookup to test the DNS queries:
```
nslookup www.ncaecybergames.org  
nslookup 192.168.8.2  
```
- If configured correctly, the DNS server will return the expected mappings.
- Updating DNS Resolver Settings
- The system must know where to send DNS queries.
- The file /etc/resolv.conf should include the DNS server’s IP:
```
nameserver 192.168.8.2  
```
- Alternatively, the network configuration (/etc/netplan/) can be updated to specify the DNS server.
- Final DNS Testing
- Refreshing a web browser with www.ncaecybergames.org should load the correct webpage.
- Reverse lookups should successfully return the domain associated with the IP.
- A properly configured DNS server enables efficient domain resolution in the Mini Hack environment.

Next in Playlist: 32 DNS Service Additional Zones