Table of Contents
What is a DNS question?
Description. A DNS query (also known as a DNS request) is a demand for information sent from a user’s computer (DNS client) to a DNS server. In most cases a DNS request is sent, to ask for the IP address associated with a domain name.
What is contained in a DNS response?
DNS is a query/response protocol. The client queries an information (for example the IP address corresponding to www.google.com) in a single UDP request. DNS uses UDP port 53 to connect to the server. TCP can also be used for response data size exceeding 512 bytes or for specific tasks such as zone transfers.
What sections can be found in the DNS query message?
The DNS protocol uses two types of DNS messages, queries and replies; both have the same format. Each message consists of a header and four sections: question, answer, authority, and an additional space. A header field (flags) controls the content of these four sections.
What are the two main categories of DNS messages?
DNS has two types of messages: query and response. Both types have the same format. The query message consists of a header and question records; the response message consists of a header, question records, answer records, authoritative records, and additional records (see Figure4).
How does a DNS server reply for a DNS query message?
DNS responses, in the case of a recursive DNS query, come directly from the DNS server that received our initial DNS query, while in the case of a non-recursive DNS query, the response arrives from the last DNS server the client (PC) queries in order to get the required DNS information. …
What is a DNS query message?
A DNS Query is a request for information sent from a DNS Client to a DNS Server. Normally a DNS Query is a request sent from a DNS Client to a DNS Server, asking for the IP Address related with a Fully Qualified Domain Name (FQDN). A DNS Query message from the DNS Client contains mainly below information.
What happens if a DNS reply exceeds 512 bytes?
Whatever the case, when the message size exceeds 512 bytes, it will trigger the ‘TC’ bit (Truncation) in DNS to be set, informing the client that the message length has exceeded the allowed size. The end symptom to the end client is usually slow DNS resolution, or inability to resolve certain domain names at all.
What is DNS Authority section?
The Authority section indicates the server(s) that are the ultimate authority for answering DNS queries about that domain. The reason for this section is that you can query any* DNS server(s) to answer a query for you.
What is DNS in distributed system?
The Domain Name System (DNS) is a distributed database system that translates domain names to numerical Internet Protocol (IP) addresses. It is an essential part of Internet infrastructure. The solution was to create a distributed system for domain name and IP address resolution.
Why do you think DNS uses UDP for DNS queries and replies?
DNS uses the User Datagram Protocol (UDP) on port 53 to serve DNS queries. UDP is preferred because it is fast and has low overhead. A DNS query is a single UDP request from the DNS client followed by a single UDP reply from the server.
Why is DNS run over UDP?
What is DNS 53?
Amazon Route 53 is a highly available and scalable cloud Domain Name System (DNS) web service. It is designed to give developers and businesses an extremely reliable and cost effective way to route end users to Internet applications by translating names like www.example.com into the numeric IP addresses like 192.0.
What are the two sections of a DNS message?
Of these, two are usually found in both queries and responses: the Header section and the Question section. I will start exploring the detailed format of DNS messages by looking at these two sections; the next topic will cover the resource record formats used by servers for the other three message sections.
What is query/response messaging in DNS?
The client/server information exchange in DNS is facilitated using query/response messaging. Both queries and responses have the same general format, containing up to five individual sections carrying information.
How long does a DNS query take to respond?
Here is the response (highlighted section in the screenshot below) to the previous DNS query sent to DNS server with IP address 139.130.4.4: Something worth paying attention to is the time it took to receive and answer to our DNS query, which was only 0.991 seconds!
What are the semantics of the various fields in a DNS?
The semantics of the various fields in a DNS message are as follows: The first 12 bytes is the header section, which has a number of fields. The first field is a 16-bit number that identifies the query. This identifier is copied into the reply message to a query, allowing the client to match received replies with sent queries.