DNS record type introduction (a record, MX record, NS record, etc.)

Ext: http://www.cnblogs.com/zcy_soft/archive/2013/09/23/3335235.html

DNS a record NS record MX record CNAME record txt record TTL value PTR value
Construction Station noun Explanation: DNS a record NS record MX record CNAME record txt record TTL value ptr value generic domain name Universal resolution domain names to bind domain name to turn
1.dns:domain Name System domain name management system domain name is composed of dots separated by a series of words or abbreviations, each domain name corresponds to a unique IP address, this named method or this management domain Name system called Domain Name management system.
Dns:domain Name server domain name servers although convenient for people to remember, but the network between the computers can only understand each other IP address, the transformation between them is called Domain name resolution, domain name resolution needs to be specialized domain name resolution server to complete, DNS is the domain name resolution server. View DNS for more detailed explanation

2. A record a (address) record is used to specify the name of the host (or domain name) corresponding to the IP addresses record. Users can point to the site server under this domain name to their own Web server. You can also set the subdomain name of the domain name. In popular terms a record is the server's IP, domain name binding a record is to tell DNS, when you enter the domain name when you boot to set in DNS a record of the corresponding server. Simply put, a record is the IP address of the specified domain name.
3. The NS record NS (name server) record is a domain name server record that specifies which DNS server the domain name is parsed by. When you register a domain name, there is always a default DNS server, each registered domain name by a DNS domain name server to be resolved, DNS server NS record address generally in the following form: Ns1.domain.com, ns2.domain.com and so on. Simply put, the NS record specifies which DNS server to resolve your domain name.
4. The MX record mx (mail exchanger) record is a mail exchange record that points to a mail server that locates the mail server based on the recipient's address suffix when the e-mail system sends the message. For example, when a user on the internet wants to send a letter to user@mydomain.com, the user's mail system finds an MX record of the domain name mydomain.com through DNS, and if the MX record exists, The user's computer sends the message to the mail server specified by the MX record.
5. The CNAME record CNAME (Canonical name) alias record allows you to map multiple names to the same computer. A computer that is typically used to provide both the WWW and mail services. For example, there is a computer named "Host.mydomain.com" (a record) that provides both the WWW and mail services for users to access the service. You can set two aliases for this computer (CNAME): www and mail, the full names of these aliases are "www.mydomain.com" and "mail.mydomain.com", in fact they all point to "host.mydomain.com".
6. TXT record
TXT records, generally refers to a host name or domain name description, such as: admin in TXT "Administrator, Tel: xxxxxxxxxxx", mail in txt "mail host, stored in XXX, Administrator: AAA", Jim in TXT "Contact:abc@mai Lserver.com ", that is, you can set up TXT content to get someone to contact you. One of the applications of TXT, SPF (Sender Policy Framework) anti-spam. SPF is a DNS-related technology, and its content is written in the TXT type of DNS records. The purpose of the MX record is to indicate to the sender what the mail server for a domain name is. The effect of SPF is the opposite of MX, which indicates to the recipient which mail server is sending mail through a domain name recognition. The role of SPF is mainly anti-spam, mainly for those senders of fake domain name spam. For example: When the mail server received the self-proclaimed sender is spam@gmail.com Mail, then in the end it is not really gmail.com mail server sent over it, we can query gmail.com SPF record, so as to prevent others to forge you to send mail.
7. TTL value TTL (time-to-live) Principle: The TTL is a value in the IP protocol packet, which tells the network router whether the time on the network is too long and should be discarded. There are a number of reasons why the package cannot be delivered to the destination for a certain amount of time. For example, an incorrect routing table might cause an infinite loop of packets. One solution is to discard the packet after a period of time and then send a message to the sender, who will decide whether to resend it. The initial value of the TTL is usually the system default, which is a 8-bit field in the header. The first idea of the TTL is to determine a time range that discards the package over that time. Because each router has at least one less TTL domain, the TTL usually represents the maximum number of routers that the packet can pass before being discarded. When the count to 0 o'clock, the router decides to discard the packet and send an ICMP message to the original sender. Simply put, the TTL is the lifetime of a domain name resolution record in a DNS server. When local DNS servers accept resolution requests, they send resolution requests to the NS server designated by the domain name to obtain resolution records, and after the record is obtained, the records are kept in the DNS server for a period of time, and if you receive a resolution request for the domain name again, Instead of making a request to the NS server, the DNS server returns directly to the record that was just obtained, which is the TTL value of the record held on the DNS server.
Application of TTL value setting:
One is to increase the TTL value to save the domain name resolution time, to speed up the site access. In general, the domain name of the various records are rarely changed, it is likely to be a few months, a few years will not change. We can fully increase the TTL value of the domain name record to allow the record to be cached in local DNS servers for a longer period of time. In this way for a longer period of time, when we visit this site, the local ISP's DNS server does not need to send a resolution request to the NS server of the domain name and return the domain name resolution record directly from the cache. The second is to decrease the TTL value and reduce the inaccessible time when changing the space. Replacement space 99.9% has a problem with DNS record changes, because of the caching problem, the new domain name record may be in place in some places, but in some places it may wait two days or even longer to take effect. The result is that some people may have access to the new server, and some have access to the old server. It's not a big deal if it's just a visit, but it's a bit of a hassle if it comes to sending a message, and maybe that important letter was sent to the old server that had been stopped.
In order to minimize the resolution time difference, the reasonable approach is: the first step, first look at the domain name of the current TTL value, we assume that 1 days. The second step is to modify the TTL value to be a minimum value that can be set, which, if possible, is 1 minutes, or 60. The third step, waiting for one day, ensures that all local DNS server caches expire and the records are updated. The fourth step is to set up a new record, where DNS can be updated to new records at the fastest speed. The fifth step is to make sure that all local DNS has been updated and set the TTL value to the value you want. The default TTL values for the general operating system are as follows: ttl=32 windows 9x/me ttl=64 LINUX ttl=128 windows 200x/xp ttl=255 Unix
8. PTR value ptr is a shorthand for pointer, which is used to map an IP address to the corresponding domain name, or it can be considered as the reverse of a record, and the reverse resolution of the IP address. PTR is primarily used for mail servers, such as mailbox AAA@XXX.com to mailboxes bbb@ Yahoo.com sent an e-mail, Yahoo mail server will see the mail when the header file, and analysis of which IP address sent out, and then according to the IP address for the reverse analysis, if the resolution of the corresponding xxx.com IP address to accept the message, the contrary will refuse to receive this email.
9. The generic domain name and the pan-resolution generic domain name are under a domain name root to *. The Domain.com form represents all of the unnamed subdomains of this domain name root. The universal parsing is the *. Domain.com's a record resolves to an IP address by accessing any prefix. domain.com can access the site you are resolving.
10. Domain binding domain name binding refers to the operation of the domain name to the server IP.
11. Domain name to redirect to the domain name or domain name forwarding, when the user's address bar to enter your domain name, will automatically jump to the other domain name you specify. Generally use the short good memory domain name to turn to complex difficult to remember domain name.