https://www.cloudflare.com/learning/dns/dns-records/dns-a-record/
The "A" stands for "address" and this is the most fundamental type of DNS record: it indicates the IP address of a given domain. For example, if you pull the DNS records of cloudflare.com, the A record currently returns an IP address of: 104.17.210.9.
A records only hold IPv4 addresses. If a website has an IPv6 address, it will instead use an "AAAA" record.
Here is an example of an A record:
| example.com | record type: | value: | TTL |
|---|---|---|---|
| @ | A | 192.0.2.1 | 14400 |
The "@" symbol in this example indicates that this is a record for the root domain, and the "14400" value is the TTL (time to live), listed in seconds. The default TTL for A records is 14,400 seconds. This means that if an A record gets updated, it takes 240 minutes (14,400 seconds) to take effect.
The vast majority of websites only have one A record, but it is possible to have several. Some higher profile websites will have several different A records as part of a technique called round robin load balancing, which can distribute request traffic to one of several IP addresses, each hosting identical content.
When are DNS A records used?
The most common usage of A records is IP address lookups: matching a domain name (like "cloudflare.com") to an IPv4 address. This enables a user's device to connect with and load a website, without the user memorizing and typing in the actual IP address. The user's web browser automatically carries this out by sending a query to a DNS resolver.
DNS A records are also used for operating a Domain Name System-based Blackhole List (DNSBL). DNSBLs can help mail servers identify and block email messages from known spammer domains.
If you want to learn more about DNS A records, you can see the original 1987 RFC where A records and several other DNS record types are defined here. To learn more about how the Domain Name System works, see What is DNS?
Không có nhận xét nào:
Đăng nhận xét