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Course: NETS 3303, Fall 2009School: Allan Hancock College
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3303 1 NETS Networked Systems DNS Bjorn Landfeldt, The University of Sydney 2 Outcomes Understanding the need for a name system Understanding the design principles of DNS Hierarchy Scalability Knowledge about standardisation organisations Bjorn Landfeldt, The University of Sydney 3 Outline Why DNS How is it organised How does it work Protocol Issues Bjorn Landfeldt, The University of Sydney 4...
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3303 1
NETS Networked Systems
DNS
Bjorn Landfeldt, The University of Sydney
2
Outcomes
Understanding the need for a name system Understanding the design principles of DNS
Hierarchy Scalability
Knowledge about standardisation organisations
Bjorn Landfeldt, The University of Sydney
3
Outline
Why DNS How is it organised How does it work Protocol Issues
Bjorn Landfeldt, The University of Sydney
4
DNS
People can't remember 145.55.23.198 People can remember bill.microsoft.com (Almost) Every networked device has identifier Fully Qualified Domain Name (FQDN)
Bjorn Landfeldt, The University of Sydney
5
FQDN
ICANN -Inet Corporation for Assigned Names and Numbers - www.icann.org
DNS administration see the FAQ for recent info
http://www.internic/net/regist.html
accredited list of registrars for .com/.net/.org
Bjorn Landfeldt, The University of Sydney
6
DNS
Two components: Name server (named)
A database front end (can be text file)
Resolver
Client side library implements gethostbyname(), gethostbyaddr()
Bjorn Landfeldt, The University of Sydney
7
DNS Hierarchy
DNS divided into levels with
root servers 2nd level servers Local servers (organisations)
Queries in iterations
First local server If not found 2nd level, then root Root points to 2nd level server etc.
Bjorn Landfeldt, The University of Sydney
8
DNS Hierarchy
root 2nd 3rd 3rd 2nd 3rd root
2nd 3rd 3rd
Host
Bjorn Landfeldt, The University of Sydney
9
Queries
Two versions:
Iterative
2nd 3rd 3rd root
Host
Bjorn 2nd Landfeldt, The University of Sydney
10
Queries
Two versions:
Recursive
2nd 3rd 3rd 2nd root
Host
Bjorn Landfeldt, The University of Sydney
11
Header
typically UDP request/reply format request = fixed header + question section reply = fixed header + query + answer sections question = (name, type, class = IP) with name in compressed format reply = set of Resource Records (RR)
Bjorn Landfeldt, The University of Sydney
12
Records
Each entry in database returned as a specific record type
A for IPv4 address AAAA for IPv6 address
Other types available
SRV, TXT etc.
Bjorn Landfeldt, The University of Sydney
13
Protocol
Bjorn Landfeldt, The University of Sydney
14
Flags
Bjorn Landfeldt, The University of Sydney
15
Resource Record format
Bjorn Landfeldt, The University of Sydney
16
RR format
domain name - same format as in query TTL - in seconds, value...
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