September 20 DNS Summary

Dns:domain Name System

The main solution is domain name and IP conversion, and the early is mainly the manual configuration of IP and domain name corresponding relationship--hosts

Related concepts:

Namespaces: He defines the hierarchy of domains used for organization names

Resource record Resouce record: It maps a DNS domain name to a specific type of resource information that is used for registering or resolving names in the namespace. In a Linux system, called the name resolution library, each row in/var/named is a resource record

DNS server: A name query that stores and answers resource records

DNS client: The resolver that queries the search returned from the server resolves the name to the record type specified in the query.

The role of the DNS system:

Forward resolution: Find the corresponding IP address based on the host name

Reverse resolution: Find the corresponding host domain name based on IP address

Distributed data structures for DNS systems:

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Root is '. ': A domain access to his root server can be this: www.magedu.com. In general, the browser will automatically complete this.

A total of 13 root servers worldwide:

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Parsing process: www.magedu.com.

Look up the local DNS record, go to root

.----. com----. magedu----www

Recursion: Focus on results only

Iteration: Also focus on the process

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DNS Server type:

Domain Name server:

The official server for a specific DNS zone, with uniqueness

Responsible for maintaining all domain-to-IP mapping records in this area

All updates to the zone are made through this server

From a domain name server

Also called a secondary domain name server

Its maintained domain name-to-IP records originate from the Domain name server

Synchronize zone data files only from the primary server or other slave servers in the same zone

Cache name servers

Also known as only cache server

Obtaining domain-to-IP records by querying other domain name servers

Cache query results locally to increase the speed of duplicate queries

Master-Slave Coordination process:

Start Authorization record:

Zone data file has version number (serial number): Serial

Refresh time (check cycle): Refresh

Retry event (retry cycle): Retry

Expiry time (expiry): expire

Negative response TTL value (cache time)

Initiates a synchronization request to the primary server after the interval reaches the time specified by refresh, and the primary server responds serial, comparing the server to the local serial, if the primary server's serial is larger than the local, and the zone data file for the master server is updated to request synchronization.

Resource record:

Soa:start of authority, in fact authorization record, a zone file has and can only have one SOA record

Ns:name server, Name server

Magedu.com in NS dns1.magedu.com. Pay attention to the last one.

@ in NS dns1 ..... Name can be omitted as

Mx:mail EXchanger, mail exchanger

@ in MX ten mx1.magedu.com. The median number is the priority level

A:address:fqdn->ipv4

Www.magedu.com. In A 1.1.1.1

Simple load balancing with different IPs for the same record

Aaaa:address:fqdn->ipv6

Ptr:pointer, pointer: Ip->fqdn

Reverse parsing:

NAME:IP address in reverse format, and append in-addr.arpa. suffix

Value:fqdn

1.1.168.192.in-addr.arpa in PTR www.magedu.com.

Cname:cononical name, official names, aliases

Web.magedu.com. In CNAME www.magedu.com//No additional A records

Specific implementation: BIND, its process is called named

Yum Install bind installation

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There are examples in sample

/usr/sbin/named: Main execution procedure

/etc/init.d/named: Service Script

Default Listener Port 53

/etc/named.conf: Master configuration file

Can be streamlined into this

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Listen-on listening address and port: divided into TCP and UDP,UDP is the query, TCP is the master-slave transmission

Directory: Working directory

Allow-query: What machine is allowed to sit and parse, can be changed to any

Recursion: Whether to turn on recursion

Logging is a log record, and all paths are based on the directory base path

Severity enables dynamic printing, and each access is back to a big labia

Zone "." In root domain:

The type is hint;

File is the root domain's parsing files

/var/named is the main working directory that holds the data files for DNS resolution records

No/etc/init.d/named, do not go on, check the information after correction

September 20 DNS Summary