Domain Name Resolution Use Case

DNS servers host data in zones,which is databases. Zones include multiple records, such as the following:

1. A 2. AAAA 3. PTR 4. MX 5. CNAME 6.SOA

A

A. Also called a host record. This record holds the host name and IPv4 address and is the most commonly used record in a DNS server. A DNS client queries DNS with the name using a forward lookup request, and DNS responds with the IPv4 address from this record.

CNAME

CNAME. A canonical name, or alias, allows a single system to have multiple names associated with a single IP address. For example, a server named Server1 in the domain ABC.com might have an alias of FileServer1 in the same domain.

DNS port

DNS servers use TCP port 53 for zone transfers. In contrast, name resolution queries use UDP port 53.

summary of DNS

DNS zones include records such as A records for IPv4 addresses and AAAA records for IPv6 addresses. DNS uses TCP port 53 for zone transfers and UDP port 53 for DNS client queries. Most Internet-based DNS servers run BIND software on Unix or Linux servers, and it's common to configure DNS servers to only use secure zone transfers. DNSSEC helps prevent DNS poisoning attacks. Nslookup and dig are two command-line tools used to test DNS. Microsoft systems include nslookup; Linux systems include dig.

MX

MX. Also called mail exchange or mail exchanger. An MX record identifies a mail server used for email. The MX record is linked to the A record or AAAA record of a mail server.

BIND

Most DNS servers on the Internet run Berkeley Internet Name Domain (BIND) software and run on Unix or Linux servers. Internal networks can use BIND, but in Microsoft networks, DNS servers commonly use the Microsoft DNS software. Occasionally, DNS servers share information with each other in a process known as a zone transfer. In most cases, a zone transfer only includes a small number of updated records. However, some transfers include all the records in the zone.

PTR

PTR. Also called a pointer record. It is the opposite of an A record. Instead of a DNS client querying DNS with the name, the DNS client queries DNS with the IP address. When configured to do so, the DNS server responds with the name. PTR records are optional, so these reverse lookups do not always work.

DNS

Primary purpose of Domain Name System (DNS) is for domain name resolution. DNS resolves host names to IP addresses. Systems are constantly querying DNS, though it is usually transparent to users. Imagine that you want to visit http://abc.com/. You enter the URL into your web browser or click a link on a page and your system queries a DNS server for the site's IP address. DNS uses UDP port 53 for these types of queries.

SOA

SOA. The start of authority (SOA) record includes information about the DNS zone and some of its settings. For example, it includes the TTL (Time to Live) settings for DNS records. DNS clients use the TTL setting to determine how long to cache DNS results. TTL times are in seconds and lower times cause clients to renew the records more often.

what does a DNS give

Sometimes, the DNS server you query knows the answer and just gives the response. Other times, it queries one or more other DNS servers to get the answer. When the DNS server queries other DNS servers, it puts the answer in its cache so that it doesn't have to do the same query again. Similarly, when clients receive answers from DNS servers, they store the answer in their cache so that they don't have to repeat the query.

AAAA

•AAAA. This record holds the host name and IPv6 address. It's similar to an A record except that it is for IPv6.