The basic concept of DNS service for Linux

How DNS is queried

1. Recursion

Recursion means that the client only needs to ask once, if the superior DNS server does not know, then the superior DNS server to find their own DNS server.

2. Iteration

The iteration means that the client needs a DNS server on its own to ask for a DNS server.

DNS Name resolution method

Forward parsing the input domain name for IP

Direction resolution input IP Find domain name

Primary and Standby DNS servers

prepared DNS records for DNS servers require constant synchronization with the primary DNS server database.

the DNS records are changed only on the primary DNS server.

How the copy operation is implemented:

Serial Number: is also the version number of the database, each modification, the version number will change once ( increment ) . The primary server can push the update content to the slave server.

Refresh time interval:refresh, check the serial number update status from the server to the primary server every how often.

retry interval:retry thetime interval between attempts to communicate from the server to the primary server after a failure. Retry interval is less than the refresh time interval

Expiration: The time interval from the server to determine the failure of the primary server. After you have determined that the primary server is invalid, stop serving from the server.

Synchronization mode:

Full-volume sync:AXFR

Incremental Sync:IXFR

Zone database files

resource record: Resource Record, abbreviated RR

Resource classification: A AAAA PTR SOA NS CNAME MX

SOA:start of authority authorization record; a zone resolution library has and can have only one SOA record, and must be in the first one.

NS:name Service domain name server record, one zone resolution library can have multiple NS Records, one of which is primary.

A: address record. fqndàIPV4

AAAA:IPV6 address record

CNAME: Alias record,Canonical Name

PTR:pointer IPàfqnd for reverse parsing

MX:Mail eXchanger Email exchanger can have multiple

priority:the smaller the 0~99 number, the higher the priority level

Definition Format for resource records

Name [TTL] in Rr_type value

SOA :

Name: The names of the current regions; For example , "magedu.com." The last point cannot be omitted. or "2.3.4.in-addr.arpa."

Value: There are several parts. 1, the zone name of the current zone ( You can also use the primary DNS server name ) 2, the current zone administrator's mailbox address, but the address can not use the @ symbol, the general use of dot number instead. 3, the master-slave service coordination attributes and the negative answer TTL.

SOA Example    : magedu.com. 86400 in SOA megedu.com. Admin.magedu.com. (2017010801;serial

2h;refresh

10m;retry

1w;expire a week

1d;negative answer TTL) The semicolon is followed by a description

NS :

Name: The region name of the current zone

Value: The name of a DNS server for thecurrent zone , such as ns.megedu.com.

NS   Example: magedu.com. 86400 in NS ns1.magedu.com.

Mx:

Name: The region name of the current zone

Value: Host name of a mail exchanger in the current zone

MS   Example:magedu.com. In MX ten mx1.magedu.com.

A:

Name: an FQDN

Value: A IPV4 address

A Example: www.magedu.com   . In A 1.1.1.1

www.magedu.com. In A 1.1.1.2

BBS.magedu.com. In A 1.1.1.1

PTR :

Name:IP address, with a specific format,IP in turn, plus a specific suffix. the address name of the normal 1.2.3.4 is 4.3.2.1.in-addr.arpa.

Value:fqnd

PTR Example  :4.3.2.1.in-addr.arpa. In PTR www.megedu.com

CNAME :

Name: aliases,aliases in fqnd format

Value: The official name of the FQDN

CNAME  Example:web.megedu.com. In CNAME www.magedu.com.

Note:1.TTL can be inherited from the global

2,@ Indicates the name of the current zone

3, the adjacent two records its name in the same time, the following can be omitted. (name below the vertical )

4,MX NS records such as the value of a fqnd , the fqnd need to have a record.

Linux's DNS service Fundamentals concept