Cloud computing tutorial learning course outline Courseware: About DNS:
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Name resolution:
NetBios名: tianyun localhost WINS hosts
FQDN: Fully Qualified Domain Name www.tianyun.com baidu.com www.126.com mail.qq.com hosts DNS Server.
A, hosts file
Role: achieving name resolution, which offers fast resolves to the local host name, cluster node
Database: planar structure, centralized database
Second, the DNS Domain Name Service
Role: Implement name resolution (such as hostname resolves to IP)
A mechanism for the host on the Internet named: namespace name space
DNS database Datebase: hierarchical, distributed database
Authoritative name servers: the actual data storage and provides an area, such as 126.com DNS server, a recording of all hosts 126.com domain, such as:
www.126.com. x.x.x.x
ftp.126.com. y.y.y.y
Authoritative name server types include:
Master: the primary DNS server, contains the original data area
Slave: The DNS server backup, the copy area data is obtained from the server through the Master (transmission region)
Non-authoritative name servers: do not store the actual data of an area, the cache only DNS server, although you can provide access, but the contents of the query does not have the authority
DNS resolution process:
Such as client resolve www.126.com
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Client queries its cache (included in the record hosts), if not send queries a DNS server in /etc/resolv.conf
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If the local DNS server authoritative for the information requested, will (authoritative answer) sent to the client.
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Otherwise (not authoritative), if the DNS server in its cache has requested information, the (non-authoritative answer) sent to the client
- If the cache is not the query information, DNS server searches for the authoritative DNS server to find the information:
a. From the beginning of the root zone, according to the DNS hierarchy search down until the information for authoritative name servers for the client obtain answers
DNS server to pass information to the client, and keep a copy in its cache, to prepare for later search.
b. forwarded to other DNS servers