Understanding how DNS works requires familiarity with the different types of queries and resource records it uses to resolve domain names into useful information. DNS query types define what kind of resource you are asking for, while resource records hold the actual data. The most common DNS query types include:

• A: returns the IPv4 address for a domain name;
• AAAA: returns the IPv6 address for a domain name;
• MX: specifies the mail exchange servers for a domain, used for routing emails;
• CNAME: defines a canonical name, allowing one domain to be an alias for another;
• NS: identifies the authoritative name servers for a domain.

Each of these query types serves a distinct purpose in the DNS ecosystem. For instance, when you want to connect to a website, your device issues an A or AAAA query to find the IP address. If you send an email, your mail server performs an MX query to determine where to deliver the message. CNAME records help manage aliases, so multiple domains can point to a single location. NS records ensure queries are directed to the correct name servers for further resolution.

When constructing or parsing DNS resource records, you need to handle several fields such as the name, type, class, time-to-live (TTL), and data length, followed by the actual data. Here is a simplified pseudo code outline for both constructing and parsing a DNS resource record:

To construct a resource record:

1. Write the domain name in DNS label format;
2. Write the record type (e.g., A, AAAA, MX, etc.);
3. Write the class (usually IN for internet);
4. Write the TTL value;
5. Write the length of the data field;
6. Write the resource data (such as an IP address or domain name).

To parse a resource record:

1. Read the domain name from the message;
2. Read the type, class, TTL, and data length fields;
3. Read the resource data based on the type and length.

This logic ensures you can both create and interpret the contents of DNS resource records, which is essential for DNS servers and clients alike.

A DNS message is a structured packet that follows a precise format for communication between clients and servers. The message is divided into several sections:

• Header: contains identification, flags, and counters for the number of questions, answers, authority, and additional records;
• Question: lists the queries being made, each with a name, type, and class;
• Answer: provides the resource records answering the queries;
• Authority: gives information about authoritative name servers;
• Additional: contains extra information to aid in resolving the query.

The question section specifies what information is being requested, such as the IP address for a domain. The answer section contains the resource records that directly respond to the query. The authority section can point to other name servers that may have the answer, and the additional section often includes helpful data like corresponding IP addresses for those servers. This structure allows DNS to efficiently resolve names and direct clients to the right resources.

Handling complete DNS messages requires converting structured data into a binary format for network transmission (serialization) and interpreting binary data back into structured form (deserialization). Here is a high-level pseudo code approach for both:

To serialize a DNS message:

1. Write the header fields (ID, flags, counters);
2. For each question, write the name, type, and class;
3. For each answer, authority, and additional record, serialize the resource record fields in order.

To deserialize a DNS message:

1. Read the header fields and counters;
2. For each question, parse the name, type, and class;
3. For each answer, authority, and additional record, parse the resource record fields.

This ensures DNS clients and servers can communicate by sending and receiving properly formatted messages, interpreting questions, and providing answers as expected.