DNS Domain Name Service Bind Berkerley Internet Name Domain

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DNSDomain Name ServiceBindBerkerley
Internet Name Domain
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DNS BIND

• Jargon
• User set up
• What it does and how it works.
• Demonstration

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Jargon

• FQDN - Fully Qualified Domain name.
• www.tmdg.co.uk is an FQDN
• But www is just a host name
• 'A records' Address records
• 'MX records' Mail eXchanger records
• 'CNAME' Alias record
• 'NS records' Name Server Records
• 'SOA' Start of Authority

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Jargon

• 'TTL' Time To Live
• Caching Only Name Servers
• Root Name Servers
• Glue Records
• Reverse DNS

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User level set up

• Normally your ISP tells you
• The IP Address of the name servers that you
  should use.
• You may be given two or three.
• It doesn't matter which one you go to really
• Quite often they are Caching Only Name Servers
• These servers normally only work for the ISP IP
  Addresses.
• If you use DHCP
• The dhcp server set up your name servers
  automagicly.

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DNS BIND

• Do I have to use it?
• What does it do?
• How does it do it?

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Why use DNS

• Names are much easier to remember.
• You can't keep track of the all the changes.
• When you change your address your name doesn't
  change.

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Domain Name Organisation

• Top Level Domains (TLD)
• .com .net .org .uk .fr .tv .me
• .co.uk .me.uk .ac.uk etc are treated like a TLD
• Second level domains are what you can register.
• uk.com pcdr.co.uk tmdg.co.uk
• Anything below the Second Level you control
• i.e. www.tmdg.co.uk mail.tmdg.co.uk
  ftp.tmdg.co.uk
• frank.tmdg.co.uk marconi.tmdg.co.uk

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DNS Tree Structure
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Resolving names.

• Root name servers.
• Direct you to a server for the TLD.
• Direct you to the name server for the domain
• They may forward you further.
• So doing it by hand-

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Resolving names.

• dig norec nostats nocmd www.tmdg.co.uk
  _at_a.root-servers.net
• I don't know but the Authority for .uk is ( a
  list of name servers. )
• One is ns1.nic.uk
• Address is
• ns1.nic.uk 195.66.240.130
• dig norec nostats nocmd www.tmdg.co.uk
  _at_ns1.nic.uk
• I don't know but the Authority for .tmdg.co.uk is
  -
• ns1.dns.houxou.com
• ns2.dns.houxou.com

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Resolving names.

• dig norec nostats nocmd www.tmdg.co.uk
  _at_ns1.dns.houxou.com
• The answer is
• www.tmdg.co.uk Is an alias (CNAME) for tmdg.co.uk
• The address of tmdg.co.uk is 192.203.240.23
• This information is good for the next
• N seconds
• N minutues
• N hours
• N days

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Reverse lookup

• Verifies you are who you say you are.
• host 193.203.240.23
• 23.240.203.193.in-addr.arpa domain name pointer
  tmdg.co.uk.
• Note the address is reversed.
• IP address are issued in blocks.
• So reversing the address makes it more like a
  domain name. Thus DNS lookups will work.

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Why not use a hosts file.

• It's fine for a home network with just a few
  hosts
• It's just not practical for larger areas and the
  owner maintains it.

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Views

• Views are new in BIND 9
• Allows you to present differing layouts to
  different places.
• Very useful if your behind a NAT Firewall
• rg.tmdg.co.uk (Router)
• william.tmdg.co.uk (printer)
• tim.tmdg.co.uk (Web Server)
• roland.tmdg.co.uk (Mail Server)

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Views for home domain
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Useful Sites

• http//www.dyndns.org/
• If you have a dynamic IP address
• http//www.DNSstuff.com
• Lots of tools to check your DNS
• Whois
• Speed tests
• http//www.DNSreport.com
• Checks you DNS entry and warns of problems

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Useful Sites

• http//www.domain-names-registration-uk.com/
• Low cost, flexible, domain name registration
• http//www.nominet.net.uk
• UK name authority

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Pitfalls with DNS

• When obtaining a domain
• Make sure you get control
• Don't use a redirect service.
• If your not sure ask some one who knows
• You may not see the need for full control now but
  you may need it in the future.

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Pitfalls

• Beware of programs that cache DNS for you
• If you have your own Domain make sure you set
  the name of your MX hosts correctly.
• It must be the hosts real name not the name you
  call it.
• It takes time for the DNS to propagate changes
• So prepare by shortening the TTL

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Questions

• Practical demo.