F5 GTM (I): DNS parameters

Study F5 GTM, Understand first DNS
Root.DNS, The global 13 individual DNS root ：

A.root-servers.net　198.41.0.4 The United States 
B.root-servers.net　192.228.79.201 The United States （ Additional support IPv6）
C.root-servers.net　192.33.4.12 The French 
D.root-servers.net　128.8.10.90 The United States 
E.root-servers.net　192.203.230.10 The United States 
F.root-servers.net　192.5.5.241 The United States （ Additional support IPv6）
G.root-servers.net　192.112.36.4 The United States 
H.root-servers.net　128.63.2.53 The United States （ Additional support IPv6）
I.root-servers.net　192.36.148.17 The Swedish 
J.root-servers.net　192.58.128.30 The United States 
K.root-servers.net　193.0.14.129 The British （ Additional support IPv6）
L.root-servers.net　198.32.64.12 The United States 
M.root-servers.net　202.12.27.33 Japan （ Additional support IPv6）

Com.DNS：

com.        54653   IN      NS      b.gtld-servers.net.
com.        54653   IN      NS      k.gtld-servers.net.
com.        54653   IN      NS      h.gtld-servers.net.
com.        54653   IN      NS      e.gtld-servers.net.
com.        54653   IN      NS      a.gtld-servers.net.
com.        54653   IN      NS      g.gtld-servers.net.
com.        54653   IN      NS      d.gtld-servers.net.
com.        54653   IN      NS      j.gtld-servers.net.
com.        54653   IN      NS      i.gtld-servers.net.
com.        54653   IN      NS      l.gtld-servers.net.
com.        54653   IN      NS      c.gtld-servers.net.
com.        54653   IN      NS      m.gtld-servers.net.
com.        54653   IN      NS      f.gtld-servers.net.

Cn.com

cn.         4321    IN      NS      a.dns.cn.
cn.         4321    IN      NS      d.dns.cn.
cn.         4321    IN      NS      b.dns.cn.
cn.         4321    IN      NS      ns.cernet.net.
cn.         4321    IN      NS      e.dns.cn.
cn.         4321    IN      NS      c.dns.cn.

COM.CN.DNS

com.cn.        1808    IN      NS      e.dns.cn.
com.cn.        1808    IN      NS      c.dns.cn.
com.cn.        1808    IN      NS      cns.cernet.net.
com.cn.        1808    IN      NS      d.dns.cn.
com.cn.        1808    IN      NS      b.dns.cn.
com.cn.        1808    IN      NS      a.dns.cn.
com.cn.        1808    IN      NS      f.dns.cn.

The preferred DNS：208.67.222.222
spare DNS：208.67.220.220

DNS A query ：

 iteration ： commonly DNS The server and DNS Queries between servers belong to this query method . When the first one DNS The server is sending to 2 platform DNS After the server makes a query request , If the first 2 platform DNS There is no required data in the server , Then it will provide 3 platform DNS Server's IP Address to No 1 platform 

 recursive ： That is to say DNS After the client sends the query request , If DNS There is no required data in the server , be DNS The server will replace the client to other DNS Service order query .

 Reverse query ： It can make DNS Client side utilization IP Address query its host name .

DNS Analytical way ：

 Forward analysis ：FQDN->IP
 Reverse DNS ：IP->FQDN

FQDN： Fully qualified domain name , Name with both host name and domain name （ example ： Host name ：zhazha, domain name ：xuexi.com,FQDN：zhazha.xuexi.com）, Logically, we can see the location of the host
Analytical process ： Find native HOST surface -> nothing , Find the DNS Server resolution

DNS Server type and relationship

 type ：
Primary name server： Primary name server 
Secondary name server
Caching-only server： Only cache reputation server 
DNS　Client
ISP　DNS
ROOT　DNS
Domain　DNS

DNS Common data types 

```bash
SOA：Start of Authority, Authorization begins , stay RFC In the definition of , Defines the global parameters of the domain 

Parameters ：

Name： domain name 
Ttl： Current record TTL value 
Class：IN=Internet
Name-server： Usually use FQDN Format 
Email-add： Administrator email address 

Sn： An unsigned integer , Maximum increment 2147483647, Usually it is 10 Digit number (yyyymmddss).
Ref：Slave Server Check regularly Master Server Of SOA Record , Determine whether to update the records of the whole domain 

Ret： When Slave Server Can't connect to Master Server Retry interval at 
Ex： Decide when records are no longer reliable (Authoritative) 
NS： Domain name server records , Used to specify the domain name by which DNS The server parses 

SOA And SN difference ：
SOA It is the starting authoritative server , You can add and delete records on this server ;
NS What does the server mean DNS The server can resolve the domain name ;
 For a domain ( Such as baidu.com)SOA only one , and NS There can be multiple .
NS The server contains SOA,SOA It's a special kind NS.

MX： Record resolution , Do email parsing , Used to specify the mail server responsible for processing the domain name sent to the recipient 

CNAME：  Called the specification name . This record allows you to map multiple names to the same computer .  Usually used to provide at the same time WWW and MAIL Computer serving .

A： Records are used to specify the host name （ Or domain name ） Corresponding IP Address record . Users can point the web server under the domain name to their own web server (web server) On . At the same time, you can also set the subdomain of the domain name .

AAAA： Is used to resolve the domain name to IPv6 Address of the DNS Record . Users can resolve a domain name to IPv6 Address , You can also resolve the subdomain name to IPv6 Address .

PTR：pointer, Equivalent to reverse DNS, Used to put a IP The address is mapped to the corresponding domain name
Method ：cmd-->nslookup-->set q=mx-->163.com
or ：nslookup -qt=mx 163.com:

The server ： Currently using server
Address： Current address
Non authoritative response (non-authoritative answer)：MX Record the four mail host names pointed to
Set q=a,
Enter the mail server host name to query ：Setq=a-->163mx00.mxmail.netease.com
or ：nslookup -qt=a 163mx03.mxmail.netease.com

Be the host IP Address
Set q=ptr, Enter the resolved address Set q=ptr-->220.181.14.139
or ：nslookup -qt=ptr 220.181.14.139

obtain IP Address of the PTR Record the hostname pointed to
TXT：TXT Record , Generally refers to the description set for a host name or domain name

DDNS： Dynamic domain name resolution system （ Peanut shell ） namely DHCP＋DNS, Give Way DHCP hold IP The change information tells DNS
Make users dynamic IP The address is mapped to a fixed domain name resolution server , Every time the user connects to the network, the client program will transmit the dynamic of the host through information transmission IP The address is sent to the server program located on the server host , The server program is responsible for providing DNS Service and implement dynamic domain name resolution .
Received DDNS After the client's update request ,DDNS Server notification DNS The server re establishes the domain name and IP Correspondence between addresses . So as to ensure that even if DDNS Client's IP Address change ,Internet Users can still access through the same domain name DDNS client .
Service principle ：

Reference resources ： https://baike.baidu.com/item/ddns/670146?fr=aladdin