dns & bind chapter 24. this chapter dns overview
Post on 31-Dec-2015
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DNS Overview
• DNS (Domain Name System) maps domain names to IP addresses, and vice versa
• It reduces the need for humans to work with IP addresses, which, with the introduction of IPv6, are complex
• BIND (Berkeley Internet Name Domain) is a popular open-source implementation of DNS
Overview
• DNS was specified in 1983 and BIND became part of BSD in 1985– Each node in the hierarchical DNS database is
called a domain and is labeled with a (domain) name
– the node at the top of the DNS hierarchy is called the root node or root domain
Reading the Hierarchy
A fully qualified domain name (FQDN) is the DNS equivalent of a file system’s absolute pathname: It is a pointer that positively locates a domain on the Internet.
The Resolver / Server Relationship
• The resolver - turns an unqualified domain name into an FQDN that is passed to DNS to be mapped to an IP address.
• The resolver always appends the root domain (.) to an unqualified domain name first, allowing you to type www.redhat.com instead of www.redhat.com. (including the trailing period) in a browser.
The Resolver / Server Relationship
• The Resolver passes the DNS request to the Name Server to begin the Process.
• The Resolver to Name Server communication is called the Recursive Query
• A recursive query sends a domain name to a DNS server and asks the server to return the IP address of the domain: The server may need to query other servers toget the answer.
The Resolver / Server Relationship
• If a name resolution request cannot be solved by DNS server it will pass the request on to “upstream servers” – this process is called an Iterative Query
• The Iterative Query sends a domain name to a DNS server and asks the server to return either the IP address of the domain or the name of the DNS server that is authoritative for the domain
Resource Records
• Information about nodes (domains) in the DNS database is stored in resource records
• There are more than 30 types of resource records exist, ranging from common types, such as address records that store the address of a host, to those that contain geographical information
Resource RecordsRecord FunctionA IPv4 Address—Maps a domain name to the IPv4 address of a host
AAAA IPv6 Address—Maps a domain name to the IPv6 address of a host
CNAME Canonical Name—Maps an alias or nickname to a domain name.
PTR Pointer—Maps an IP address to a domain name and is used for reverse name resolution
NS Name Server—Specifies the name of the system that provides domain service (DNS records) for the domain
SOA Start of Authority—Designates the start of a zone. Each zone must have exactly one SOA record. An authoritative server maintains the SOA record for the zone it is authoritative for
Installing DNS
• Install the following packages:• bind• bind-utils (provides dig among other utilities)• system-config-bind (optional)• bind-chroot (optional)
Starting and Checking the Service
• Run chkconfig to cause named to start when the system enters multiuser mode:# /sbin/chkconfig named on
• After you have configured named, start it with service:# /sbin/service named start
Named is the name of the DNS daemon
Summary
• DNS uses a hierarchical method for resoling Host names
• Recursive queries involve the Client/Server• Iterative queries involve the Server/Server• Linux DNS requires the manual create of
records• System-config-bind is the utility for viewing
DNS in GUI form
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