SLIDE 1
URLs
URLs
- K. Cooper1
1Department of Mathematics
URLs Introduction
URLs K. Cooper 1 1 Department of Mathematics Washington State - - PowerPoint PPT Presentation
URLs K. Cooper 1 1 Department of Mathematics Washington State - - PowerPoint PPT Presentation
URLs URLs K. Cooper 1 1 Department of Mathematics Washington State University 2014 URLs Introduction URL Universal Resource Locater A way to specify any file publicly available on the World Wide Web Aka Universal Resource Identifier a
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URLs Introduction
URL
http:
- scheme
// www.math.wsu.edu
- name or IP address
[:80]
- port
/faculty/welcome.php
- directory path to file
[#G]
input to file
scheme The means of interaction with the machine name The identifier for the machine where the file resides port The network interface for the program we must interact with path The location of the file on the directory structure
- n that machine
input If the file is a program, allows us to specify input; if it is not, we can specify a location inside the file
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URLs Scheme
Protocols
A collection of formats and rules for exchanging messages among computers Can essentially amount to a language In a URL, tells the browser how to go about contacting the remote computer, whether the transaction is to be encrypted
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URLs Scheme
HTTP
HyperText Transfer Protocol Protocol used in transferring hypertext markup among computers. When it is encrypted, it is called HTTPS.
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URLs Scheme
SSH
Secure SHell A protocol that supports running commands on a remote machine Replaced old telnet – an unencrypted protocol Uses public key encryption SSH1 – 56-bit encryption key SSH2 – 128-bit encryption key
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URLs Scheme
FTP
File Transfer Protocol Protocol used for transferring arbitrary files among computers One of the oldest transfer protocols Insecure – don’t use this Can be tunneled through SSH, though that is problematic A more modern version is SFTP - Secure FTP , a new protocol that is encrypted while streamlining the TCP functions of FTP
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URLs Scheme
File
A scheme (not protocol) to obtain files from the local computer Cannot be used to get files from remote machines Uses only local directory structure
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URLs Scheme
Others
Mailto – send mail to another machine through a browser POP , IMAP – get mail from another machine LDAP – Get directory information Gopher – Old menu-based file transfer About – (Usually) local information and settings
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URLs Addresses
Addresses
After the scheme there is a colon and two slashes. Tim Berners-Lee says he wishes he had left out the two slashes. After that comes the identifier of the machine we are trying to get pages from. Note that we can find out whether a host is on the network using ping. ping www.washington.edu
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URLs Addresses
IP
Internet Protocol breaks files into packets, provides addresses and info for delivery describes unique addresses for devices on the Internet IPV4 – addresses are four octets, written with period separators e.g. 134.121.45.19 – numbers usually written as decimal 0–255. about 4.3 billion addresses – not even one per person IPV6 – addresses are eight 16-bit numbers, written with colon separators
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URLs Addresses
ARP
Address Resolution Protocol finds local IP addresses based on broadcast arp -a
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URLs Addresses
Routing
ARP unsatisfactory for a large network Internet is compartmentalized - subnetwork Routers have two (or more) addresses - gateways from
- ne subnet to another
If a router sees a destination IP that is not known to it, then the packet goes to another gateway default gateway route -n
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URLs Addresses
Names
Humans are not good at remembering numbers Machines get names Names must be mapped to addresses using DNS
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URLs Addresses
DNS
Domain Name System Certain servers (nameservers) are responsible for resolving names for small subnetworks If a nameserver cannot resolve a name, it passes the request to a higher level nameserver Top-level nameservers mostly know which nameservers to pass requests down to. Eventually the request is resolved by the authoritative server for a given subnetwork
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URLs Addresses
DNS
From https://en.wikipedia.org/wiki/File:An_example_of_theoretical_DNS_recursion.svg
dig www.wikipedi.org
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URLs Addresses
TCP
Transmission Control Protocol Breaks a message into smaller chunks for transmission
- ver a network
Reliably tracks the chunks for reassembly in order at the destination If packets are lost, sends them anew Part of the TCP/IP suite The TCP port provides a network address for a TCP process on a computer
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URLs Addresses
TCP Ports
80 – the default port attached to web server programs 443 – the default port attached to SSL (secure) web servers 21 – the (old) default port for FTP servers (switches to 20 for transfer) 22 – the default SSH port 25 – the default mail port 53 – the (old) default for DNS
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URLs Addresses
Ethernet
Most popular local networking technology Works based on unique address for each ethernet interface MAC – Media Access Code six octets, separated by colons first three octets denote manufacturer
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URLs Addresses
Network Packets
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URLs Paths
File Systems and Files
Directories listed starting at the document root Most of the file system is not public First slash “/” represents the document root Each slash after that indicates going down one level into the file system /math/faculty/mbenz/index.html indicates that we seek a file called index.html that is inside the mbenz directory, which is inside the faculty directory, which is inside the math directory, which is inside the document root directory.
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URLs Paths