I believe we usually work are inseparable from the DNS resolution, DNS resolution is the first step to access the Internet, whether using a laptop or open a browser to access the network when the phone APP, the first step to access network resources is bound to be a DNS resolution Process. Below we will explain to you in detail the relevant knowledge of DNS.
What is DNS
DNS is the Domain Name System, is a core service of the Internet, is used to implement domain and a distributed database that maps IP addresses to each other, enabling users to more easily access the Internet, without having to remember the machine can be read directly IP number of strings. By its host name, the host name to obtain the IP address corresponding to the domain name resolution process is called (or host name resolution).
The domain structure parsing
As shown above, the domain structure is a tree structure, the root server on behalf of the top of the tree, the root of one is known by our .com, .net, .cn other universal domain and .cn, .uk other countries domains, known as top-level domain. Online registration of domain names are basically two domain names, such as baidu.com, taobao.com and so the two domain names, they are essentially owned enterprise management and operation and maintenance personnel. Followed by three or four domain names, not much go into details here. In summary, the overall domain structure mechanism is integral to the local.
DNS resolution process
As shown above, we will elaborate DNS resolution process.
1, the first position is a client computer or cell phone, open the browser in the future, such as input www.zdns.cn domain name, it is above all a DNS resolution request initiated by the browser, if the local cache server can not find results , you will first query to the root servers, each server is the location where the top-level domain root server which records when requested www.zdns.cn to the root of the root server returns the location information .cn server.
2, the recursive server after server address to get .cn authority, the authority will be asked to find cn server know www.zdns.cn position. This time cn authoritative server to find and return address zdns.cn server.
3, continue to zdns.cn authoritative server to query this address, the address given by the zdns.cn server: 202.173.11.10
4, the final link to http, the successful visit.
5, here add that once the recursive server to get the resolution records will be cached locally, if the next time the client then requests the local recursive name server's domain name the same time, it will not happen again checked layer by layer because the local server which has been cached, this time directly to the www.zdns.cn a record is returned to the client on it.
DNS resource records
Recording a mapping between domain name information , call resource record ( RR).
When we query the domain name www.zdns.cn record structure query results obtained with the following data:
1, TTL, is the life cycle, recursive server will save the resource record length of time in the cache.
2, network / protocol type, its logo represents the IN, IN is the internet, the current DNS main support system protocol is IN.
3, type, is a resource record type, general site are all A records (host IPv4 addresses).
4, rdata resource record data is the domain name associated information data.
tips:
Below we list a few common resource record types:
A: Address address, IPv4
AAAA: Address IPv6 address
NS: Name Server Domain Name Server
SOA: Start of Authority start of authority
MX: Mail Exchanger Mail Exchange
CNAME: Canonical Name canonical name
PTR: Pointer pointer
TXT：Text
SRV：Service
DNS classification server
Common DNS server is two types: authoritative analysis server and recursive resolution server. Recursive resolution server can also be called localDNS.
Authoritative resolution server
Authoritative DNS server holds the data part of the domain name space in the region. If the DNS server is responsible for the jurisdiction of one or more areas, said this authoritative DNS server for the server in these areas.
Root authoritative DNS resource records labeled secondary or authoritative server is designated as a region DNS server authoritative servers. Server listed by resource records, other servers it is considered the authoritative server for that zone. This means that any server specified in the NS resource records are treated as other sources of authoritative server, and the query contains the name of the region can acknowledgment.
Recursive server
Recursive server Under normal circumstances, when there is no initial DNS data, DNS data inside all of it comes from the query results to the authority resolution server, once the inquiry is completed, will form a recursive server in the local time according to TTL cache recording, and provides the user query DNS resolution service, which is a recursive function server.
tips:
Q: When we modify the DNS resolution service record, we should amend or modify the recursive authority inside the inside?
A: All records DNS resolution which types of changes are made to modify the authority resolution server inside.