published priority 12 30 min. 50 XP.

DNS Fundamentals. Records, Resolvers, Zones

DNS lookups power four of the 13 scored NCAE services. This lesson teaches the vocabulary you need. what a record is, what a zone is, the difference between authoritative and recursive. so when you read `named.conf` later, you already know the concepts.

DCWF roles: IT-441 Network Operations Specialist IT-451 System Administrator Services: DNS EXT FWDDNS EXT REVDNS INT FWDDNS INT REV

Objectives

Know the common DNS record types: A, AAAA, CNAME, MX, NS, SOA, PTR, TXT
Distinguish forward (nameIP) from reverse (IPname) lookups
Understand the difference between authoritative vs recursive resolvers
Read a zone file and identify SOA, NS, and resource records
Use `dig` to query any DNS server for any record type
Interpret NXDOMAIN vs NOERROR + empty answer

Quick reference

Command	Purpose
dig <name>	Default A record lookup
dig <name> AAAA	IPv6 (AAAA) record
dig <name> MX	Mail server record
dig <name> NS	Name servers for a domain
dig <name> TXT	Text records (SPF, DKIM, verification)
dig +short <name>	Just the answer, no ceremony
dig @<dns-server> <name>	Ask a specific resolver
dig +trace <name>	Follow the delegation chain from root
dig -x <ip>	Reverse lookup (IP name via PTR)
host <name>	Simpler output than dig
nslookup <name>	Interactive resolver
getent hosts <name>	Goes through NSS. includes /etc/hosts

Common pitfalls

Confusing NXDOMAIN (name doesn't exist) with NOERROR + empty answer (name exists, but no record of this type)
Missing the trailing dot on FQDNs. `example.com` vs `example.com.` matters in zone files
Forgetting that PTR records live in a special reverse-zone naming scheme (`in-addr.arpa`)
Querying your own resolver and not understanding it may be cached. use `dig +trace` or `@localhost` explicitly
Leaving recursion enabled on an authoritative server. lets anyone on the internet use you as a resolver (DNS amplification attack)

How it works (walkthrough)

# DNS record types at a glance:
#   A       name   IPv4        example.com.    IN A      93.184.216.34
#   AAAA    name   IPv6        example.com.    IN AAAA   2606:2800:220:1::2c
#   CNAME   alias  real name   www.example.com. IN CNAME  example.com.
#   MX      mail routing        example.com.    IN MX     10 mail.example.com.
#   NS      nameserver          example.com.    IN NS     ns1.example.com.
#   SOA     zone authority      example.com.    IN SOA    ns1 admin serial . 
#   PTR     reverse lookup      34.216.184.93.in-addr.arpa. IN PTR example.com.
#   TXT     arbitrary text      example.com.    IN TXT    "v=spf1 . "

# Authoritative vs recursive:
#   Authoritative server: has the zone file, knows the records firsthand
#     (your BIND at 192.168.10.12 for team10.ncaecybergames.org)
#   Recursive resolver: doesn't have the zone; asks authoritative servers on your behalf
#     (your ISP's DNS, 8.8.8.8, 1.1.1.1)
#   A well-configured NCAE BIND is authoritative for YOUR zones,
#   NOT recursive for the world.

Skill drills