INLS 102 Internet Basics

1
INLS 102 Internet Basics

2
Housekeeping

• Any questions about material so far?
• Use email signup for Inls102-1 list
• Get SSH at http//software.unc.edu/
• SILS Ruby Windows accounts OK
• Volunteers for Oral Presentation?
• Project 1 on class website, due 1/24

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Loose Ends

• Cat 5 cable twist
• ARP big picture

4
Network Basics

• (7-layer) OSI Reference Model

(http, etc.)
TCP, UDP
IP, ICMP
packet, mac address
wires, radio
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Network Example

• How does network packet get sent from A to D?

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Routers

• Layer 3 operation, uses IP addresses
• Find routes between different IP address ranges
• a.k.a. different network segments

7

• Privatized in 95

Source http//moat.nlanr.net/INFRA/Images/t3.gif
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Internet Backbones

• Backbones are major data pipelines that tie
  smaller networks together
• E.g., NSFNET (previous slide)
• Ensure quality of service
• Private backbones http//www.nthelp.com/maps.htm
• Next generation network (ATN) guarantees quality
  of service

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TCP/IP

• Conventional reference to the two main protocols
  used on the Internet
• IP Level 3 network address protocol
• Described briefly above
• Includes routing conventions
• TCP Level 4 data transport protocol

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TCP General Idea

• Handshake both sides agree on connection
• Disassembles information into packets and adds
  the information required to reassemble
• Headers includes IP, port number, packet number
• Payload data itself
• Trailer contains checksum information that the
  receiving system uses to see that the data has
  not been corrupted in transit (otherwise ask for
  retry)
• Ensures reliability by accounting for packets
• If a packet gets lost, the receiver requests a
  resend

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TCP -- What to Connect

• Both origin destination characterized by
• IP address
• Port number (Whats This?)
• Allows server to handle more than one service
• E.g., web (port 80)
• E.g., ftp (port 21)
• Allows client to handle more than one connection
• Temporary ports assigned by operating system
• Web reply goes to same port the request came from
• Ditto ftp both can be happening at the same time

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TCP -- What to Connect

• So what is actually being connected by TCP is
• Specific internal process widget on origin system
• Specific internal service widget on destination
  system
• There may be many connections between any two
  systems, involving various processes within them
• The IP address (typically just one per system)
  isnt enough information to manage this much
  activity
• Hence the port number (on both sides)

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Domain Name System (DNS)

• Few people want to remember everything by IP
  address ?
• Hierarchical names unc.edu, ils.unc.edu,
  ruby.ils.unc.edu
• top-level domains
• .edu education
• .com, .biz commercial
• .gov government
• .org community organizations
• Complete list http//www.iana.org/gtld/gtld.htm
• Country-codes
• .fr France, .ca Canada, .au Australia
• Complete list http//www.iana.org/cctld/cctld-whoi
  s.htm

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DNS

• Decide whats your top-level domain (IANA)
• E.g., .fr
• Buy 2nd level domain name from DNS provider
• E.g., maybe Id like xyzzy.fr
• Have to find a provider who does .fr
• Typically have to pay each year (so its rent,
  not buy)
• 3rd level names (if any) are up to you

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Uniform Resource Locator (URL)

• Web address is a typical URL
• service_typeport_number//host-name/file-or-dire
  ctory-pathname
• e.g., http//ils.unc.edu/bmeyers/
• Service types (a.k.a. protocol names)
• http hypertext transport protocol
• https ditto, plus encryption
• ftp File transfer protocol
• Case INsensitive, except filename part (depends
  on host)
• Browsers typically assume http// (and www. ) if
  you omit

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Windows Commands That Reveal Internet Settings

• hostname
• ipconfig
• nslookup
• ping
• tracert
• arp

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Class Exercise (P1/2)

• Open Windows command interpreter
• Start -gt Run, and type cmd
• Start -gt Programs -gt Accessories -gt Command
  Prompt
• To get help, type command /help -- e.g., ping
  /help
• To find out your computers network name, type
  hostname
• To find out your IP configuration settings
  ipconfig /all
• To see your machines current internal cache of
  known ethernet (IP) addresses vs. physical (MAC)
  addresses arp -a

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Class Exercise (P1/2)

• To find out about another computer use nslookup
  (domain name server lookup)
• nslookup isis.unc.edu
• nslookup 152.2.1.217
• To find out about response times
• ping www.unc.edu
• To trace the route to a host
• tracert www.ils.unc.edu

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This Week

• By the end of this week you should be able to
• Describe the OSI 7-layer network model
• Explain in general how the 4 lowest layers work
• Describe how a domain name is constructed
• Use tools to identify the IP address that
  corresponds to a domain name, and vice versa
• Describe the format and meaning of a URL

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For Next Class

• Read SAMS Teach Yourself Unix
• Lessons 1-2 (pp. 1-28
• Lessons 4-5 (pp. 47-75) (ignore KDE)
• Read carefully. Keep brain engaged. The book is
  not a 100 match to our environment, nor a 100
  perfect book.
• Bring laptop. Have SSH working.