DNS Learning Notes

DNS A records NS records MX record CNAME record txt record TTL value PTR value

1. DNS

Dns:domain Name System domain name management systems domain name is composed of dots separated by a string of words or abbreviations, each domain name corresponds to a unique IP address, this named method or the system of managing domain name is called Domain Name management system.

Dns:domain Name server domain name servers, although convenient for people to remember, but the network of computers can only know each other IP addresses, the conversion between them is called Domain name resolution, domain name resolution needs to be dedicated to the domain name resolution server to complete, DNS is the server for domain name resolution.

2. A record

A (address) record is the IP address record used to specify the hostname (or domain name). Users can point the Web server under the domain name to their own Web server. You can also set the subdomain name of the domain name. In layman's terms a record is the server's IP, domain binding a record is to tell the DNS, when you enter the domain name when you boot to the set in the DNS of a record corresponding to the server. Simply put, the a record is the IP address that corresponds to the specified domain name.

3. NS Records

The NS (name server) record is a domain name server record used to specify which DNS server the domain name is to be parsed.

When you register a domain name, there is always a default DNS server, each registered domain name is a DNS domain name server to resolve, the DNS server NS record address generally in the form of the following: Ns1.domain.com, ns2.domain.com and so on.

Simply put, the NS record is the specified DNS server that resolves your domain name.

4. MX record

The MX (mail Exchanger) record is a mail exchange record that points to a mail server that is used to locate the mail server based on the address suffix of the recipient when the e-mail system sends the message. For example, when a user on the internet wants to send a letter to [email protected], the user's mail system looks up the MX record for the domain name mydomain.com through DNS, if the MX record exists, The user's computer sends the message to the mail server specified by the MX record.

5. CNAME record

CNAME (Canonical name) alias record, which allows you to map multiple names to the same computer. Typically used for computers that provide both WWW and mail services. For example, there is a computer named "Host.mydomain.com" (a record), which provides both the WWW and mail services, in order to facilitate user access to the service. You can set two aliases (CNAME) for this computer: www and mail, the names of both aliases are "www.mydomain.com" and "mail.mydomain.com", and in fact they all point to "host.mydomain.com".

6. TXT record

TXT record, generally refers to a hostname or domain name description, such as: admin in txt "Administrator, Phone: Xxxxxxxxxxx", mail in txt "mail host, stored in XXX, Manager: AAA", Jim in the txt "Contact: [Email Protected] ", that is, you can set the TXT content in order for others to contact you.

One of the applications of TXT, SPF (Sender Policy Framework) anti-spam. SPF is a DNS-related technology whose contents are written in the DNS TXT type record. The purpose of the MX record is to indicate to the sender what the mail server for a domain name is. The role of SPF, in contrast to MX, indicates to the recipient that which mail servers are sent via a domain name endorsement. The role of SPF is mainly anti-spam, mainly for those who forged the domain name of the sender of Spam mail. For example: When the mail server received a message claiming that the sender is [email protected], then it is not really gmail.com mail server sent over, we can query gmail.com SPF record, in order to prevent others to forge you to send e-mail.

7. TTL value

TTL (time-to-live) Principle: TTL is a value in the IP protocol package that tells the network router if the packet is too long in the network and should be discarded. There are many reasons why a package cannot be delivered to a destination for a certain period of time. For example, an incorrect routing table may cause an infinite loop of the package. One solution is to discard the package after a period of time, and then give the sender a message that the sender decides whether to resend. The initial value of the TTL is usually the system default, which is the 8-bit domain in the header. The initial idea of TTL is to determine a time range over which to discard packets. Since each router has to reduce the TTL domain by at least one, the TTL usually indicates the maximum number of routers the packet can pass before it is discarded. When counted to 0 o'clock, the router decides to discard the packet and sends an ICMP message to the original sender.

Simply put, the TTL is the lifetime of a domain name resolution record in the DNS server. When the DNS server in the local region receives the resolution request, it sends the resolution request to the NS server specified by the domain name to obtain the parsing record, and after obtaining this record, the record will be stored in the DNS server for a period of time, and if the domain name is resolved again during this period, Instead of making a request to the NS server, the DNS server will return directly to the record that was just obtained, and the time that this record is retained on the DNS server is the TTL value.

8. PTR value

PTR is a shorthand for pointer, which maps an IP address to the corresponding domain name, or it can be viewed as a reverse of a record, and a reverse resolution of the IP address.

PTR is mainly used for mail server, such as mailbox [email protected] to email [email protected] sent a mail, Yahoo mail server when the mail will see the header file of the message, and analysis is by which IP address issued by, Then, according to the IP address of the reverse resolution, if the resolution of the corresponding xxx.com IP address to accept the message, and vice-versa refused to receive the message.

9. Pan-domain name and pan-resolution

A generic domain name refers to a domain name under the root of *. The domain.com form represents the domain root of all the non-established sub-domains.

Pan-Parse is to put *. domain.com a record resolves to an IP address by accessing any prefix. domain.com can access to the site you are parsing.

10. Domain Binding

Domain name binding refers to the operation of pointing a domain name to a server IP.

11. Domain Name Steering

Domain redirection is also referred to as the domain name direction or domain forwarding, when you enter your domain name in the user address bar, will automatically jump to the other domain name you specified. It is generally the use of short, well-remembered domain names to turn to complex and difficult to remember domain names.

This article is from the "Godben" blog, make sure to keep this source http://godben.blog.51cto.com/8919725/1828124

DNS Learning Notes