DNS records serve distinct purposes in the domain name resolution process. While both are essential for proper domain functioning, they operate at different levels:

• A Records map a domain name directly to an IPv4 address (e.g., example.com → 192.0.2.1)
• NS Records delegate authority for a domain or subdomain to specific nameservers

Consider this typical zone file configuration:

; Zone file for example.com
$TTL 3600
@       IN SOA  ns1.example.com. admin.example.com. (
                2023081501 ; serial
                7200       ; refresh
                3600       ; retry
                1209600    ; expire
                3600 )     ; minimum

; Nameserver records
@       IN NS   ns1.example.com.
@       IN NS   ns2.example.com.

; A Records
@       IN A    192.0.2.1
www     IN A    192.0.2.1
ns1     IN A    203.0.113.1
ns2     IN A    203.0.113.2

The coexistence of A and NS records in the same zone file typically occurs in these scenarios:

1. Self-referential NS records: When your domain hosts its own nameservers (like ns1.example.com)
2. Subdomain delegation: When preparing to delegate a subdomain to different nameservers

Here's how you might delegate a subdomain while maintaining the parent domain's A records:

; Parent domain zone file (example.com)
blog.example.com.    IN NS    ns1.bloghosting.com.
blog.example.com.    IN NS    ns2.bloghosting.com.

; Meanwhile at bloghosting.com's nameservers
; Zone file for blog.example.com
@       IN A     198.51.100.42

Watch for these issues when working with A and NS records:

Use these commands to inspect your DNS configuration:

# Check A records
dig example.com A +short

# Check NS records
dig example.com NS +short

# Trace full resolution path
dig example.com +trace

DNS records serve distinct purposes in domain resolution. An A record (Address record) directly maps a domain or subdomain to an IPv4 address. This is what ultimately tells clients where to find your server.

example.com.    IN  A   192.0.2.1
sub.example.com. IN A  203.0.113.5

An NS record (Name Server record) delegates authority for a domain or subdomain to specific DNS servers. These name servers are then responsible for providing the authoritative answers about that domain's records.

example.com.    IN  NS  ns1.example.com.
example.com.    IN  NS  ns2.example.com.

This apparent redundancy serves important purposes in DNS hierarchy:

1. Glue Records: When the name servers are within the domain they serve (like ns1.example.com), their A records must exist in the parent zone to avoid circular dependencies.
2. Delegation: Even if you have A records in your zone file, NS records tell the internet which servers are authoritative for your domain.
3. Subdomain Management: NS records allow delegating subdomains to different DNS providers or servers.

Consider this real-world setup where both record types work together:

; Zone file for example.com
$TTL 3600
@       IN  SOA  ns1.example.com. admin.example.com. (
                2024010101 ; serial
                3600       ; refresh
                900        ; retry
                604800     ; expire
                3600       ; minimum TTL
)

; Name servers
@       IN  NS   ns1.example.com.
@       IN  NS   ns2.example.com.

; Glue records
ns1     IN  A    192.0.2.1
ns2     IN  A    198.51.100.1

; Main website
@       IN  A    203.0.113.10
www     IN  CNAME example.com.

; Subdomain delegation
blog    IN  NS   ns1.thirdparty.com.
blog    IN  NS   ns2.thirdparty.com.

Here are frequent issues developers encounter:

• Missing Glue Records: When name servers are subdomains but lack A records in parent zone
• Inconsistent TTLs: NS records and their corresponding A records should have matching TTLs
• Improper Delegation: Forgetting to update NS records when changing DNS providers

Use dig to verify your setup:

dig +trace example.com
dig NS example.com
dig A example.com @ns1.example.com

For programmers managing infrastructure:

// Programmatically check records using Python
import dns.resolver

def check_records(domain):
    try:
        # Check NS records
        ns = dns.resolver.resolve(domain, 'NS')
        print(f"Name servers: {[str(r) for r in ns]}")
        
        # Check A records
        a = dns.resolver.resolve(domain, 'A')
        print(f"IP addresses: {[str(r) for r in a]}")
    except Exception as e:
        print(f"DNS error: {e}")

check_records('example.com')