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