Performing a DNS scan with NMAP (Network Mapper) can indeed be a critical task for systems administrators, developers, and other IT professionals. DNS (Domain Name System) is the protocol that translates human-friendly URLs into numerical IP addresses that servers use to identify each other. An understanding of this process, and the ability to scan and analyze it, is crucial for maintaining network security and efficiency.
Firstly, one must have NMAP installed on their system. NMAP is a free and open-source network scanning tool. It is used for network discovery and security auditing. It is available for all major operating systems including Windows, Linux, and macOS. It can be downloaded from the official NMAP website.
After the successful installation, a DNS scan can be conducted using NMAP. To perform a basic DNS scan with NMAP, the following command can be used in the Terminal on Linux/macOS or Command Prompt on Windows:
nmap -p53 —script dns-brute target.com
In this command, -p53 refers to port 53, where DNS services usually run. “—script dns-brute” tells NMAP to use its “dns-brute” script, which is designed to enumerate DNS hostnames by brute force guessing of common subdomains. “target.com” should be replaced with the domain you want to scan.
Other DNS-related scripts can be found with: nmap —script “dns-\*”
One important thing to note is the “nmap —script dns-cache-snoop” command which checks whether a DNS server (target) is vulnerable to snooping its cache records, revealing domains that have recently been resolved by the targeted DNS server.
For a reverse DNS lookup, the command nmap -R target.com can be used where -R option will conduct a PTR record request for the IP address to reveal the associated hostnames.
For a more comprehensive DNS scan, a zone transfer scan (a method of replicating DNS databases across a group of server) could be performed by the “dns-zone-transfer” script with
nmap —script dns-zone-transfer -p 53 target.com
Please remember that these scans should only be performed on the network and hosts that you own or have permission to scan, as unsolicited scanning can be considered as intrusion activity and is against the NMAP’s usage policy.
Sources:
NMAP Official site (https://nmap.org)
DNS Enumeration with NMAP: https://n0where.net/dns-enumeration-with-nmap
NMAP Network Scanning Book by Gordon Lyon (https://nmap.org/book)
NMAP DNS Enumeration Scripts – https://nmap.org/nsedoc/categories/dns.html
