DNS Issues for Website Accessibility

A.

The A record of a public website is used to associate a domain name with the IP address of the server hosting the website. When the A record is updated, it can take some time for the change to propagate throughout the internet's DNS system. This is because DNS servers store cached copies of DNS records to reduce the load on the root DNS servers.

In this scenario, some visitors are unable to access the website, which indicates that their DNS servers have not yet received the updated A record. To address the issue, the TTL (Time To Live) value of the A record should be adjusted.

The TTL is a value in the DNS record that specifies the maximum amount of time that a DNS resolver should cache the record. By default, the TTL for an A record is typically set to a value of several hours or even a day, meaning that once a DNS resolver caches the record, it will continue to use that cached value until the TTL expires.

To ensure that the updated A record is propagated quickly, the TTL value should be reduced to a shorter period, such as 5 minutes or less. This will cause DNS resolvers to update their cached records more frequently, allowing the updated A record to propagate more quickly throughout the DNS system.

The MX (Mail Exchange) record is used to specify the email server for a domain and is not relevant to website access. The TXT (Text) record is used to provide additional information about a domain, such as SPF (Sender Policy Framework) records for email authentication, but does not affect website access. The SOA (Start of Authority) record is used to identify the primary DNS server for a domain and is not relevant to website access in this scenario.