Transcript (Representation of …) URLs, IP addresses in

(Representation of …)
URLs, IP addresses
in the computer era
114 – Lecture 8
U-R-L
Static URL
http://www.wellesley.edu/Resources/about/index.html
Access method
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Server and domain
Uniform Resource Locator
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T. B-L wanted URI: Universal
Resource Identifier
It tells you where something is
located, i.e.,
the name of the server that has it
It also tells you how you could get it
Path
•
•
•
•
•
•
•
•
Document
gov - Government agencies
edu - Educational institutions
org - Organizations (nonprofit)
mil - Military
com - commercial business
net - Network organizations
ca – Canada
kz–…
2/11/2009
Harvard Bits
3
URL invoking a web program
Dynamic URL
http://www.db-url.com/website-monitor.html?gclid=CLfYzO_bq5QodzReMiw
Access method
Server and domain
Web program
Parameter
Dynamic fake URL
http://wiki.answers.com/Q/What_does_URL_mean
Access method
Server and domain
Web program and parameter
Clients and Servers
Web Server
Web Server
e-mail Server
www.wellesley.edu
cs.wellesley.edu
firstclass.wellesley.edu
download
THE INTERNET
Client Computers
upload
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You have been enumerated
• Every server is enumerated in an IP address
• IPv4: 32 bits written as 4 decimal numerals up to 256,
e.g. 149.130.12.213 (Wellesley College)
– How many addresses can it represent?
– IPv6: 128 bits written as 8 blocks of 4 hex digits each,
e.g. AF43:23BC:CAA1:0045:A5B2:90AC:FFEE:8080
– How many addresses are in IPv6?
• Client translates URLs to IP addresses,
e.g. cs.wellesley.edu  149.130.136.19
– Uses authoritative sites for address translation
a.k.a: “Domain Name Server” (DNS)
What is your IP address?
IP: Internet Protocol
What is the Internet?
“Ten movies streaming across that, that Internet, and what
happens to your own personal Internet? I just the other day
got...an Internet was sent by my staff at 10 o'clock in the
morning on Friday. I got it yesterday [Tuesday]. Why?
Because it got tangled up with all these things going on the
Internet commercially.
[...] They want to deliver vast amounts of information over
the Internet. And again, the Internet is not something that
you just dump something on. It's not a big truck. It's a
series of tubes. And if you don't understand, those tubes
can be filled and if they are filled, when you put your
message in, it gets in line and it's going to be delayed by
anyone that puts into that tube enormous amounts of
material, enormous amounts of material.”
Senator Ted Stevens, Chair,
Comm. on Commerce, Science and Transportation
(charged with regulating the internet)
What is the Internet?
No really, what is it?
https://www.youtube.com/watch?v=ewrBal
T_eBM
(Communicating through …)
HTTP and TCP/IP Protocols
in the web era
114 – Lecture 9
A nuts and bolts view of Internet
client
• The Internet is a network of networks
consisting of:
routers
– hosts (can be can be either
modem
clients or servers)
– communication links
of varying bandwidths
– routers (switching devices)
– modems translate bits to travel correctly
through wires and air
• A client program running
on a host, following a protocol,
requests and receives a file
from a server program
running on another system
• We call such programs processes
Network Protocols and HTTP
server
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ARPAnet, 1971
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Handshake
Sending and receiving information
Network Protocols and HTTP
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IP ~ Lower
Level Protocols
TCP ~ Higher Level Protocols
TCP/IP vs Postal Mail Protocols
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TCP/IP: Basic Protocols
• TCP: Transport Control Protocol
– Creates logical connection b/w two machines on the network
– Makes connected machines think
that they are directly connected
– Provides reliable, perfect transport of messages
• IP: Internet Protocol
– Breaks data into packets to move through routers
– Tries hard, but may drop packets
• We usually talk about TCP/IP
– TCP uses IP and guarantees delivery
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Message pipelining
•
When the message is segmented into packets, the network is said to
pipeline message transmission.
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• Standards, although they are merely
• conventions, give rise to vast innovation, if
they are well chosen, spare, and
• widely adopted.
Packet switching
•
Messages are broken into packets each of which travels from the source to
destination through a maze of routers and links.
•
Packet switching achieves much higher efficiency than full-file travel
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Traceroute from gaia.cs.umass.edu
3 delay measurements
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms
3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms
4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms
5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms
6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms
7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic
8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms
link
9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms
10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms
11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms
12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms
13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms
14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms
15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms
16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms
17 * * *
no response
18 * * *
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
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HTTP: HyperText Transfer Protocol
• HTTP is the Web’s
client/server protocol.
• User agent (browser)
implements the client side of
HTTP.
• Web pages generally consist
of an HTML file which
references other objects
(JPEG, Java applet, video,
audio clips).
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HTTP/1.0 nonpersistent connection
http://www.someSchool.edu/someDir/file.html
1a. Client initiates
a TCP connection to
www.someSchool.edu
2.
4.
Client sends
HTTP request for file
/someDir/file.html
Client receives response.
terminates connection,
examines file, and may
request other files.
1b. Server at host
www.someSchool.edu
accepts connection
and acknowledges.
3.
Server receives
message, finds and
sends file
in HTTP response.
5.
Steps 2, 3, 4 are
repeated for each
requested file.
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HTTP request message
request line
(GET, POST,
HEAD commands)
header
lines
GET /someDir/file.html HTTP/1.0
Host: www.someSchool.edu
User-agent: Mozilla/4.0
Connection: close
Accept-language:en,fr
Carriage return,
line feed
indicates end
of message
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HTTP response message
status line
(protocol
status code
status phrase)
header
lines
requested
HTML file
HTTP/1.0 200 OK
Connection: close
Date: Thu, 06 Aug 1998 12:00:15 GMT
Server: Apache/1.3.0 (Unix)
Last-Modified: Mon, 22 Jun 1998 …...
Content-Length: 6821
Content-Type: text/html
data data data data data ...
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Testing HTTP using telnet
Type:
telnet cs.wellesley.edu 80
Type:
GET /~mir/index.html HTTP/1.0
Opens TCP connection to
port 80
Issues a GET request to
HTTP server
(you must hit carriage
return twice at the end).
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Some HTTP response status codes
200 OK
request succeeded, requested object in this message
301 Moved Permanently
requested object moved, new location specified in this message (Location)
400 Bad Request
request message not understood by server
404 Not Found
requested document not found on this server
505 HTTP Version Not Supported
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SMTP (mail) protocol
The sending process must simply
specify
– the name or address
of the host machine
(hostname or IP address), and
– The process on that host that will handle
the received message
(port number).
– Mail port is usually 25
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