By Thomas Davis
September 24, 2001
Introduction
DNS resolver
DNS architecture
DNS protocol
DNS load balancing
WHOIS
Problems
3. Internet performance problems are generally
not server problems. For many web sites,
Keynote's measurements demonstrate that
most of their performance problems occur out
in the Internet's infrastructure somewhere
between the web site and its users: at the
NAPs (Network Access Points) where
backbone providers interconnect, in one or
more routers along the communication path,
or in a DNS (Domain Name Service) close to
the user.
From
http://www.keynote.com/measures/top10.html
gethostbyname()
gethostbyaddr()
The Domain Name System (DNS) is an
unreliable database with distributed
data and mangement
A resolver maps names to IP addresses
using name servers
Library functions:
Most generic domains (.com, .edu, etc) are
international, but .gov and .mil are USspecific.
E.g., “pan.eecs.lehigh.edu.”
A host has a domain name specified using a
sequence of names, each of which may be
up to 63 characters long, separated by
periods.
Names are case insensitive
A domain is an absolute domain name or a
fully qualified domain name (FQDN) if it ends
with a period.
com
pan
eecs
lehigh
edu
gov
ie
mil
arpa
arpa
net
org
us
You typically need a primary name server and one or more
secondary name servers.
Secondary retrieves information from primary using a zone
transfer.
A zone must provide multiple name servers. This
server records the members in the domain.
Second-level domains (“colorado.edu”) are usually an
independent zone
Most sub-domains (“cs.colorado.edu”) are independent.
E.g., most universities (not ours!) have departmental
domains that are then independently administered
A zone is a subtree of the DNS tree that is
independently managed
.gov
.edu
.mil
government
education
military
US-only” Top Level Domains
“Generic” Top Level Domains
commercial
• .com
organization
• .org
network
• .net
~ 240 ISO Top Level Domains
.af
Afghanistan
.ca
Canada
.dk
Denmark
.fr
France
.uk
United
Kingdom
.us
USA
.zw
Zimbabwe
.aero – Air-transport industry
.biz – Business
.coop – Nonprofit cooperatives
.info – Unrestricted use
.museum – Museums
.name – individuals
.pro – Accounts, lawyers, and physicians
Elected officials worldwide
Domain Name used as of Aug 2000
Internet domain names
Internet Protocol address numbers
protocol parameter and port numbers
Internet Corporation for Assigned Names and
Numbers (ICANN)
Created in October 1998 by a broad coalition
of the Internet’s business, technical,
academic, and user communities
Coordinates
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798
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243
-
H
ARIN – American Registry
for Internet Numbers
APNIC – Asia-Pacific
Network Information Centre
RIPE NCC – Reseaux IP
Europeens Network
Coordination Cenntre
G
G
10
DNS resolver
1
Web browser
LAN
9 DNS Response
2 DNS Query
Local DNS
server
Dns cache
I
8
3
7
Second-level
Domain server
Top-level
6 Domain server
5
4
Root Server
J
M
L
K
J
Iterative – the receiving DNS server
responds directly with the DNS client
with the IP address if the DNS servers
for the zone at the next level
Recursive – the receiving DNS server
resolves the entire request itself.
K
N
Connectionless protocol
Used in order to avoid TCP establishment
delays
Mostly UDP, TCP used mainly for zone
transfers
UDP – User Datagram Protocol
Either UDP or TCP
N
O
O
Q
Caches both positive and negative
responses
TTL – Number of seconds to cache the
address
Done at the server and browser level
Based on the TTL of the DNS response
P
DNS records can have multiple address
for one domain name
DNS uses round robin sequences to
return addresses
Con: No intelligence
R
S
U
U
U
Firewall
Dial-up
Might have to contact specific registries
Not all addresses can be fully resolved
http://www.networksolutions.com/cgibin/whois/whois
In-addr.arpa
Reverse lookups
T
V
V
W
Y
Y
Y
Can be a central source of failure
Who owns american.com? Who should own
it?
What about america.com? (no “n”)
Domain name resellers (greatdomains.com)
Any one can register any domain for a
small fee (great in theory)
This causes massive problems
X
Z
Introduction
DNS resolver
DNS architecture
DNS protocol
DNS load balancing
WHOIS
Problems
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