DNS - RYO Blog

What is DNS (Domain Name System)?#

DNS translates domain names (like www.hackthebox.com) into IP addresses (like 104.22.3.84). Think of it like a phone book for the internet.

It doesn’t use a central database — DNS info is distributed globally across thousands of name servers.

Types of DNS Servers#

Server Type	Description
DNS Root Server	Top-level servers managed by ICANN that resolve TLDs (.com, .net). Only queried when other servers can’t answer.
Authoritative Nameserver	The official source for domain records. Provides definitive answers for its zones.
Non-authoritative Nameserver	Answers queries using cached data obtained from other servers, not from zone files.
Caching DNS Server	Temporarily stores DNS records to improve performance. Respects TTL values from authoritative servers.
Forwarding Server	Passes DNS queries to designated resolvers instead of resolving them directly.
Resolver	Client-side component (in devices/routers) that initiates DNS lookup requests.

Security & Privacy#

DNS traffic is unencrypted by default, making it susceptible to spying. To improve privacy:

DNS over TLS (DoT)
DNS over HTTPS (DoH)
DNSCrypt

Common DNS Records#

Record	Purpose	Example Use Case
A	Maps domain to IPv4 address	`example.com → 192.0.2.1`
AAAA	Maps domain to IPv6 address	`example.com → 2001:db8::1`
MX	Specifies mail servers	`10 mail.example.com`
NS	Delegates to authoritative nameservers	`ns1.example.com`
TXT	Contains text data (verification, email security)	`"v=spf1 include:_spf.google.com ~all"`
CNAME	Creates domain aliases	`www → example.com`
PTR	Reverse DNS (IP to name)	`1.2.0.192.in-addr.arpa → example.com`
SOA	Zone administration details	`Primary nameserver, admin email, serial number`

Example: Using `dig` to find SOA#

dig soa www.inlanefreight.com

Result:

SOA Record found for inlanefreight.com
Email: awsdns-hostmaster@amazon.com (dot replaced with @)
Server: ns-161.awsdns-20.com

DNS Server Configuration (BIND9)#

1. Local Config Files#

/etc/bind/named.conf.local
/etc/bind/named.conf.options
/etc/bind/named.conf.log

2. Zone Files#

Located at: /etc/bind/db.domain.com

Example entry:

@ IN SOA dns1.domain.com. hostmaster.domain.com. (
2001062501 ; serial
21600 ; refresh
3600 ; retry
604800 ; expire
86400 ) ; minimum TTL
IN NS ns1.domain.com.
IN A 10.129.14.5
www IN CNAME server2

Reverse Lookup Files#

Located at: /etc/bind/db.10.129.14

Example PTR:

5 IN PTR server1.domain.com.

Dangerous Settings#

Misconfigurations can expose the DNS server to attacks. Some common issues:

Too open allow-query settings
Allowing zone transfers publicly
Running outdated BIND versions (vulnerabilities listed at CVEdetails)
Prioritizing functionality over security