Domain name a record, MX record, cname, TTL

What is a record?
The A (Address) record is used to specify the IP address record corresponding to the Host Name (or domain name. You can direct the website server under this domain name to your web server. You can also set a second-level domain name for your domain name.
What is an MX record?
The mail route record. You can direct the mail server under the domain name to your own mail server, and then you can control all mailbox settings on your own. You only need to enter the IP address of your server online to transfer all emails under your domain name to your own email server.
What is a cname record?
That is, the alias record. This record allows you to map multiple names to the same computer. It is usually used on computers that provide both WWW and mail services. For example, there is a computer named "host.mydomain.com" (a record ). It provides WWW and mail services at the same time, in order to facilitate user access to the service. You can set two aliases (cname) for the computer: WWW and mail. The two aliases are www.mydomain.com and "mail.mydomain.com ". In fact, they all point to "host.mydomain.com ".
What is the TTL value?
The full name of TTL value is "time to live". Simply put, it indicates the cache time of DNS records on the DNS server. To understand the TTL value, take a look at the following example:
Assume that the IP address of the domain name myhost.abc.com (in fact, this is a DNS record, which usually indicates that there is a host named myhost in the abc.com domain) is 1.1.1.1, and its TTL is 10 minutes. This domain name or record is stored on a DNS server named dns.abc.com.
Now there is a user in the browser to type the address (also called URL): http://myhost.abc.com what will happen at this time?
The DNS server specified by the visitor (or its ISP, Internet service provider, which is dynamically allocated to him) 8.8.8.8 tries to explain myhost.abc.com to him, of course, because the DNS server 8.8.8.8 does not contain the message "myhost.abc.com", it cannot be resolved immediately. However, after recursive queries by global DNS, the DNS server "dns.abc.com" is finally located, dns.abc.com: the DNS server sends the IP address 1.1.1.1 of myhost.abc.com to 8.8.8.8, and then 8.8.8.8.8 tells the user the result. 8.8.8.8 in order to accelerate the resolution of the myhost.abc.com record in the future, the 1.1.1.1 result will be retained for a period of time. This is the TTL time, during this period, if the user has another resolution request for the myhost.abc.com record, it will directly tell the user 1.1.1.1. When the TTL expires, the above process will be repeated.
The resource record survival time during the query process. When the client requests domain name resolution, it always stores some domain name cache information. These cached files can be used to respond to resolution requests of the same site in the future, instead of accessing the server every time. However, these cached files also have a shelf life and will expire. This shelf life is defined in a parameter returned by a resolution request. This parameter is TTL ). The survival time ensures that the DNS server does not store outdated data. The cache file survival time can be defined in the DNS database: each resource record can be defined through the TTL field; each region can be defined through authorization (SOA) the minimum TTL field of the record. You can also define the maximum TTL for storing resource records on the client. There are two important factors to consider when defining the TTL. One is the accuracy of the cache information, and the other is the frequency of use of the DNS server and the degree of network congestion.
If TTL is short, the possibility of using old information is greatly reduced, but the load on DNS servers and networks is increased. If TTL is short, the cached information may be out of date, and the customer may receive incorrect information, reducing the load on the DNS server and the network.
If the resolution request is from the cache, the TTL will also be passed along. In this way, the client can know the TTL of the relevant information, and the client will not change the TTL of the accepted TTL based on its TTL, DNS database updates are required because the resource records in the region file can change. Here I will simply mention that there are two types of DNS database updates: static updates and dynamic updates.