DNS translates human‑friendly hostnames into IP addresses (and vice versa), ensuring seamless communication over IP networks. It operates at the Application Layer (OSI Layer 7) and uses UDP 53 by default, falling back to TCP 53 for larger responses or zone transfers.

• How DNS Work

1- DNS Record Types

https://www.youtube.com/watch?v=HnUDtycXSNE

Each record consists of: Name, Type, Data, and TTL (Time to Live).

• A (Address)
  • Purpose: Maps a hostname to an IPv4 address.
  • Example: example.com. IN A 192.0.2.1
• AAAA (IPv6 Address)
  • Purpose: Maps a hostname to an IPv6 address.
  • Example: example.com. IN AAAA 2001:db8:85a3::8a2e:370:7334
• CNAME (Canonical Name)
  • Purpose: Alias one name to another; the resolver restarts lookup at the target.
  • Example: www.example.com. IN CNAME example.com.
• MX (Mail Exchange)
  • Purpose: Specifies mail servers for a domain with priority.
  • Syntax: <name> IN MX <preference> <mail-server>
  • Example: example.com. IN MX 10 mail.example.com.
• NS (Name Server)
  • Purpose: Authoritative name servers for a zone.
  • Example: example.com. IN NS ns1.example.com.
• PTR (Pointer)
  • Purpose: Reverse lookup / maps an IP to a hostname.
  • Example: 1.2.0.192.in‑addr.arpa. IN PTR example.com.
• SOA (Start of Authority)

  • Purpose: Zone metadata and zone‑transfer parameters.

  • Fields: Primary NS, admin email, serial, refresh, retry, expire, minimum TTL.

  • Example:

    example.com. IN SOA ns1.example.com. hostmaster.example.com. (
        2025052201 ; serial
        3600       ; refresh
        900        ; retry
        1209600    ; expire
        3600       ; minimum TTL
    )
    

Record stores administrative information about a DNS zone

• DNS Zone
• TXT (Text Record)

Used for metadata and verification (e.g., SPF, DKIM, DMARC).

"v=spf1 include:_spf.example.com ~all"
"v=DKIM1; k=rsa; p=PUBLIC_KEY"
"v=DMARC1; p=reject; rua=mailto:[email protected]"

SRV (Service Location)