Different DNS record types (for example, A, AAAA, TXT, pointer records, alias records)

What is the primary purpose of an A record in DNS?

The primary purpose of an A record, or Address Record, is to map a domain name to its corresponding IPv4 address. It allows users to access a website by typing in a familiar domain name instead of the numerical IP address.

How does an AAAA record differ from an A record in DNS?

An AAAA record is similar to an A record but it is used to map a domain name to an IPv6 address, which is a newer and larger address space compared to the IPv4 address space that A records map to.

What type of DNS record would you use to verify domain ownership and implement email security policies, such as SPF, DKIM, or DMARC?

TXT records are used to provide arbitrary text values associated with a domain, including verification of domain ownership, and implementation of email security policies like SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting & Conformance).

Can you explain what a CNAME record is and when you might use it?

A CNAME record, or Canonical Name record, is used to create an alias that points to another domain name. It is typically used for subdomains where multiple subdomains point to the same IP address, so instead of updating individual A or AAAA records, you only need to update the primary domain’s record.

What is a PTR record and what is its significance in DNS?

A PTR record, or Pointer record, maps an IP address (IPv4 or IPv6) to a domain name, essentially the reverse of an A or AAAA record. It’s commonly used in reverse DNS lookups, where the identity of an IP is verified, which can be important for security purposes, such as fighting spam.

For what purpose would you use an SRV record in DNS?

SRV records, or Service records, are used to identify the hostname and port number for specific services, such as VoIP, instant messaging, and other communication protocols. They allow service discovery and load balancing by directing traffic to specific servers running these services.

What is the difference between an Alias record in Route 53 and a traditional DNS CNAME record?

An Alias record in AWS Route 53 is used to map resource record sets to Elastic Load Balancers, CloudFront distributions, or S3 buckets that are configured as websites. Unlike CNAME records, Alias records can point to root domains (e.g., example.com), and they resolve to A or AAAA records while not incurring additional query charges. They also recognize changes in the IP addresses of the resources they map to.

When configuring a DNS zone, in what scenario would you prefer to use an Alias record over a CNAME record in AWS Route 53?

You would prefer to use an Alias record over a CNAME record when you need to map a root domain (apex DNS name) to an AWS resource like an ELB, a CloudFront distribution, or an S3 bucket configured for website hosting, as CNAME records do not support root domains. Alias records also automatically resolve to the updated IP addresses of AWS resources, which can simplify DNS management.

Explain the purpose of an MX record in the DNS system.

An MX record, or Mail Exchange record, specifies the mail server responsible for receiving email on behalf of a domain. It includes a priority field allowing for backup mail servers to be used in a specific order if the primary server is unavailable.

What is the significance of the SOA record in a DNS zone file?

The SOA record, or Start of Authority record, is crucial as it provides authoritative information about a DNS zone, including the primary name server, the email of the domain administrator, the domain serial number, and other essential values such as the refresh, retry, expire, and minimum TTL (time to live) periods. It is a critical part of managing DNS transfer and replication processes.

In the context of AWS Route 53, how does a weighted routing policy work with DNS records?

In a weighted routing policy in AWS Route 53, you assign different weights to DNS records to proportionally direct traffic to multiple resources. This can be useful for load distribution or testing new versions of software against the current version. DNS queries are answered in proportion to the weight assigned to individual records, allowing for controlled traffic flow.

What purpose does a DNS NS record serve, and how is it used in domain delegation?

An NS record, or Name Server record, indicates which DNS servers are authoritative for a particular zone. It is used for domain delegation, where a domain’s owner can specify which DNS servers should control its DNS records. When a domain is registered, its NS records are set up to point to the registrar’s name servers unless they are custom-configured to point to alternative DNS servers.