Intranet Installation

1
Intranet Installation

• Domain Names - Part 2

2
Linux as a DNS Server

• The popular UNIX DNS package Berkley Internet
  Name Domain (BIND) by the Internet Software
  Consortium also contains a server program called
  named
• named can be configured to act in different modes
• caching server
• zone DNS server

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Using named as a Workstation Cache Server

• This is the easiest way to use named
• It can be set up to cache all DNS responses
• In fact all configurations of named are caching
  servers
• You must configure the /etc/named.conf file
• This tells the named program where the file for
  the root servers are kept

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Using named As a Zone DNS Server

• A Zone DNS server looks after a domains Zone file
• It uses the same file as a caching server,
  /etc/named.conf
• Zone DNS servers can either be Primary or
  Secondary for the Zone

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DNS Database Records

• Each DNS server is responsible for keeping track
  of the hostnames in its zone
• To do this it must a have a method of storing
  host information in a database
• The DNS database is a text file that consists of
  resource records (RRs) that describe computer
  function
• The DNS servers database first has to declare
  the zone that it is responsible for

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DNS Database Records

• It must declare each host computer in its zone
• Finally it can declare special information such
  as email and name servers
• Some common records are
• SOA Start of Authority
• A Internet Address
• NS Name Server
• CNAME Canonical name (nickname or alias)
• HINFO Host Information
• MX Mail Server
• PTR Pointer

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Start of Authority Record (SOA)

• Each database starts with an SOA record that
  defines the zone
• The format for the SOA record is
• domain name TTL class SOA origin person (
• serial number
• refresh
• retry
• expire
• minimum)

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Start of Authority Record (SOA)

• domain name is the name of the zone that is being
  defined (the _at_ sign can be used to signify the
  domain)
• TTL is the time in seconds that a requesting
  computer will keep any DNS information from this
  zone
• class is the protocol that is being used (always
  IN)
• origin is the name of the computer where the
  master zone database is located (must have a
  trailing period . )

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Start of Authority Record (SOA)

• person is an email address of a person
  responsible for the zone
• serial number is a unique number that identifies
  the version of the zone database file (use date
  plus version count 2002022100)
• refresh is the time in seconds that a secondary
  DNS server should query a primary DNS server to
  check the SOA serial number. If it is different
  it will request an update (One hour or 3,600
  seconds is common)

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Start of Authority Record (SOA)

• retry is the time that a secondary DNS server
  should retry after a failed refresh attempt
• expire is the time that a secondary DNS server
  can use the date from the primary DNS server
  without getting refreshed (42 days or 3,600,000
  is common)
• minimum is the time that should be used as the
  TTL in all RRs in this zone (1 day or 86,400
  seconds)

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Internet Address Record (A)

• Each host in the zone defined by the database
  should have a valid A record to define its
  hostname to the Internet.
• The format is
• host TTL class A address
• host is the fully qualified hostname for the
  computer
• address is the IP address of the computer

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Canonical Name (CNAME)

• Besides a normal hostname, many computers also
  have nicknames.
• Useful if you want to identify particular
  services without having to rename computers in
  the domain. The format is
• nickname TTL class CNAME hostname

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Name Server Record (NS)

• Each zone should have at least two DNS servers.
  NS records are used to identify these servers to
  other DNS servers trying to resolve hostnames
  within the zone.
• The format is
• domain TTL class NS server

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Name Server Record (NS)

• domain is the domain name of the zone that the
  DNS server is responsible for
• server is the hostname of the DNS server. There
  should be an associated A record to identify the
  IP address of the DNS server

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Host Information Record (HINFO)

• Additional information about a computer can be
  made available to DNS server by using the HINFO
  record.
• The format is
• host TTL class HINFO hardware software
• host is the hostname of the computer
• hardware is the type of hardware the computer is
  using
• software is the OS type and version of the
  computer

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Pointer Record (PTR)

• In addition to an A record, each computer in the
  zone should also have a PTR record.
• This allows the DNS server to perform reverse
  queries from the IP address of the computer
• The format is
• IN-ADDR name TTL class PTR name

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Pointer Record (PTR)

• IN-ADDR name is the reverse DNS name of the IP
  address
• name is the hostname of the computer

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Mail Server Record (MX)

• Most important are the MX records
• They instruct remote mail servers where to
  forward mail for your zone
• The format is
• name TTL class MX preference host

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Mail Server Record (MX)

• name is the zone name, also can be a host name
• preference is an integer signifying the order in
  which remote servers should try connecting if
  multiple mail servers are specified

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Example DNS Database for a Domain

• TTL86400_at_ IN SOA pc1.ne.it-dmit.com.
  hostmaster.ne.it-dmit.com. ( 2001081301 86
  400 300 864000 3600
  ) IN NS pc1.ne.it-dmit.com.. IN MX 10
  mail.ne.it-dmit.com.pc1 IN A 10.1.17.5yellowsta
  r IN A 10.1.17.3bluestar IN A 10.1.17.2www IN C
  NAME pc1mail IN CNAME pc1ftp IN CNAME pc1

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Activity

• Session 4 Activity Page 21 in Study Guide
• Configure your Linux computer to resolve queries
  to the DNS server 192.168.17.xx (your IP address)
• Configure your own zone file with a domain name
  of your number.intra.com.
• Use the dig command and query your DNS server.