Domain Name Service

1

• Domain Name Service
• (DNS)

2
DNS
Domain Names
Internet Objects
unix.eg.bucknell.edu
athena.eg.bucknell.edu
mail.eg.bucknell.edu
perseus.eg.bucknell.edu
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From Symbolic Name to Address
4
Hierarchy
5
Zones Name Servers
Zone Each one is implemented by two or more name
servers (redundancy) but one server can implement
more than one zone.
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Hierarchy of Name Servers
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Resource Records

• Tuple

Type A Value is an IP address
Type NS Value is the domain name
for a server that can resolve a given name
Type CNAME Value is the canonical
name for a host
Type MX Value is the domain name
for a host running a mail server for the domain.
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Examples

• ltprinceton.edu, cit.princeton.edu, NS, INgt
• ltcit.princeton.edu, 128.196.128.233, A, INgt

ltcisco.com, ns.cisco.com, NS, INgt ltns.cisco.com,
128.96.32.20, A, INgt
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Examples

• ltcs.princeton.edu,gnat.cs.princeton.edu,MX,INgt
• ltcicada.cs.princeton.edu,192.12.69.60,A,INgt
• ltcic.cs.princeton.edu,cicada.cs.princeton.edu,CNAM
  E,INgt
• ltwww.cs.princeton.edu,192.12.69.35,A,INgt
• ltcicada.cs.princeton.edu,roach.cs.princeton.edu,CN
  AME,INgt

10
Name Resolution
Problem Given that there exist three levels of
identifiers (domain names, IP addresses, and MAC
addresses), determine the sequence of steps the
system goes through to map a domain name, say
ugly.dude.com to the corresponding MAC address.