Overview
This lecture explains the purpose and structure of DNS zones, their management through zone files, and the function of different DNS resource records, including reverse lookups.
DNS Zones and Authority
- Authoritative name servers manage DNS requests for specific DNS zones, not just entire domains.
- DNS zones are hierarchical, with root servers authoritative for the root zone and TLD servers for TLD zones.
- Zones do not overlap; each is responsible for a distinct section of the DNS hierarchy.
- Administrative control is delegated downwards, enabling organized management at multiple levels.
DNS Zone Management
- DNS zones simplify managing large numbers of resource records by dividing domains into sub-zones.
- Large organizations can split their domain into zones (e.g., la.largecompany.com) for easier management.
- Each DNS zone typically has its own authoritative name server.
- Multiple physical servers can act as authoritative servers for a zone to ensure reliability.
Zone Files and Resource Records
- Zone files are configuration files listing all resource records for a given DNS zone.
- Each zone file must contain an SOA (Start of Authority) record, which declares the zone and its authoritative server.
- NS (Name Server) records list other servers also responsible for the zone.
- Zone files usually contain records like A (IPv4), AAAA (IPv6), CNAME (canonical names), and default TTL (Time to Live) values.
Reverse Lookup Zones
- Reverse lookup zone files allow DNS to map IP addresses back to FQDNs (fully qualified domain names).
- These files use PTR (Pointer) records instead of A/AAAA records.
Key Terms & Definitions
- Authoritative Name Server — Server responsible for answering DNS queries for a specific DNS zone.
- DNS Zone — A segment of the DNS namespace managed by a specific entity.
- Zone File — Text file listing all DNS resource records for a zone.
- SOA Record — Start of Authority; indicates the primary server and basic properties of the zone.
- NS Record — Name Server; specifies which servers are authoritative for the zone.
- A Record — Maps domain names to IPv4 addresses.
- AAAA (Quad A) Record — Maps domain names to IPv6 addresses.
- CNAME Record — Maps one domain name to another.
- PTR Record — Pointer; used in reverse DNS to map IP addresses to domain names.
- TTL (Time to Live) — Value indicating how long records should be cached.
Action Items / Next Steps
- Review resource record types and their purposes.
- Understand how to organize and delegate domains into multiple DNS zones.
- Practice creating a sample zone file, including SOA, NS, and other records.