Local

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Local Inter Networks
Design template Globe

• from here to the world
• 25 September 2009

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How do networks work?

• Software
• an application asks for or receives data
• another software packetizes the data and
  addresses the envelope to send to...
• Hardware
• the network computer receives these packets and
  pushes them out the door over...
• Wires and Electronics
• the cable connecting the computer to the network
  electronics
• which forwards the packets to other electronics
  until they get to their destination

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Switches
Example System 1.A seeking System 2.B

• Switches work by keeping track of the systems
  located off their ports
• if the system that is sought is not connected to
  that switch, the switch will send the request to
  other switches until it is able to find the
  switch that contains the sought system.

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Internal Switches

• So, in Manning, we have several switches, several
  servers, and several networks
• Our switches and "main" servers for the building
  plug into the main switch for Manning itself.

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Ethernet

• Most of the Ethernet ports in SILS have a speed
  set to 100mb.
• In comparison, the wireless ports are set to
  about 11.7 mb.
• The speed on the wireless is limited by the
  current available technology.

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In Manning

• Each wiring closet contains Tier 1 switches, to
  which are connected cat5 utp wires.
• Which themselves are connected to the main switch
  in the main closet.
• Which itself is the fiber uplink to the Tier 2
  switches.

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Within Manning

• Within Manning hall there are 3 networking
  closets to serve parts of the buildings.

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Within Manning

• There is a closet on the 2nd floor

• The 3rd closet is in the 5th floor stacks

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Within Manning

• The main closet located off the SILS Computer Lab
  has the fiber uplink to the campus network going
  into it.
• This is a 1 Gbit uplink.

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Moving out into the star
Manning Hall

• The core switches are then linked out to other
  Tier 2 Switches that provide links to other
  buildings near them.
• In each building, there are switches to provide
  ports for each wall port.
• For each port on the wall, there is a port
  somewhere on a switch that it is connected to.
• for the most part, there are in fact more wall
  ports than switch ports, so in some cases not all
  the ports in a building can be connected at once.

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UNC Campus

• The campus is laid out in a "star" topology in
  which central switches are linked in a star
  fashion.
• Different devices can be connected to a switch.
• can include other switches, computers, wireless
  access points, or any other network device.

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UNC Campus
Phillips Hall

• A main "core" set of three (for redundancy)
  switches are located in the control center in the
  basement of Phillips.

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UNC Campus
Cisco Kid

• Phillips uplinks to the commodity internet (the
  "real" internet) through Cisco Kid to MCNC(our
  ISP).
• We have a 2.4 Gbit uplink to the internet through
  this. We share a link with many of the other
  universities and school in North Carolina.
• CiscoKid is our main router that does all the
  "work" of finding addresses and managing traffic
  into, and out of our network.

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Internet Principles
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History ...

• ARPA managed (and funded) for 15 years

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History ...

• 1986 - NSF took over
• Give the technology to the masses not just MIT
• NSF funded the backbone for 7-8 years
• Connectivity proliferated

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History ...

• 1994 - NSF ceased direct support
• Now funded by the market, government, industry

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Access to information
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Internet Structure
Applications Web Clients, PC Apps, ...
Services Naming, Mail, File Transfer
Conventions Protocols, standards
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Whats a host?

• Its an Internet connected computer with
• an Internet address,
• (perhaps) a domain name.
• An internet address
• Is a unique, 4-byte integer.
• Unambiguously identifies a computer (actually a
  network interface card)
• Lets back up ...

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The Internet Evolved

• Started as 4 machine demonstration - ARPANET
  (UCLA, UCSB, SRI, Utah)
• But to link them into networks
• Conventions, or standards, were needed
• Thus was born TCP/IP, which provided
• Interoperability across heterogeneous machines
• End-to-end communication
• Reliability in the face of data link failures

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TCP/IP????

• Stands for Transmission Control
  Protocol/Internet Protocol
• Provides reliable, in-order, end-to-end
  transmission of data
• consider the alternative

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More on Protocols

• IP makes sure the envelope is addressed in the
  same way so that anyone could receive it
• TCP is more like sending a certified letter - you
  get a response that someone has received it. TCP
  also makes sure that the parts of the letter are
  all received and are IN ORDER
• Application layer protocols (i.e. HTTP, FTP)
  ensure that the sender and receiver are speaking
  the same language, and that the letter can be
  interpreted

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Packets

• In reality, each letter is sent in a bunch of
  pieces - as if you had sent it one page at a
  time.
• These pieces are packets.

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A possible piece of the Internet
Could be us
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A possible piece of the Internet
Local Area Network
But here we are
Routers
They are there
Ruby 152.2.81.1
www.bahn.de 81.200.192.68
Cisco Kid
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Suppose Harry talks to Sally ...
Harry.com
Sally.edu
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Suppose Harry talks to Sally ...
Overly simplified, IP gets it to the right
place, TCP puts the pieces back together in order
Harry.com
Sally.edu
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More about Servers

• Servers can be physical computers
• Servers can also be software applications
• One server (physical computer) can run many
  servers (software applications) at a time
• For example, Isis has several
• listproc
• web
• ftp
• mail
• address book
• So, how does the application know when the data
  being received is for it?

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Ports

• Each software server listens on a different
  port
• Some common ports are
• FTP (20,21)
• telnet (23)
• smtp (25)
• web (80)
• The combination of IP address and port number
  dictates where the data goes
• So who assigns ports? IANA (Internet Assigned
  Numbers Authority)

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More on clients

• For any given application, there can be many
  clients
• People are more familiar with clients, since they
  interface with them directly
• Examples of clients are
• Netscape Navigator, Internet Explorer, Mozilla
• WS-FTP, SSH, SecureCRT

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Lets use the web as an example

• The client (your web browser) sends a request for
  a URL to a server
• The server finds the requested page and sends it
  back to the client
• The protocol used is called HTTP (HyperText
  Transfer Protocol)
• Many different types of clients, and many
  different types of servers

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The Client/Server/Protocol Relationship
Client Initiates a Connection
Server Waits Responds to Incoming Connections
IP Addr 152.2.81.103
IP Addr 152.2.81.1
Server Application
Client Application
(A Program running on this machine)
(A Program running on this machine)
Application Protocol (HTTP)
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Anatomy of a URL

• URL stands for Uniform Resource Locator
• sometimes seen as Universal Resource Locator
• Example http//ils.unc.edu/library

Protocol
hostname
Domain name
Item requested
http//
ils.
unc.edu/
library
But how does one find that name on the Internet?
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Naming vs. Addressing
Harry.com
Sally.edu
Names are tied to IP addresses
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How does Harry find Sally?

• Sally.edu is a name, not an address
• Could be 152.2.81.1
• An Internet Address is
• 4 byte (32 bit) number
• 4 billion hosts possible (in theory, but...)
• Doled out by IANA (or surrogate)
• Internet Assigned Numbers Authority
• ensures adjacency, no clashes

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Why Names?

• So one could use 207.46.130.149 instead of
  www.microsoft.com
• IP addresses for configurability and
  administrative control,
• but names for human memory
• To connect the two, we use

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The Domain Name System (DNS)

• Sally.edu is a domain name
• Interspersed all over the internet are
  specialized servers that translate names into IP
  addresses
• A DNS server stores the name/address pair.
• Domain Name System is hierarchical

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DNS Example
ruby.ils.unc.edu
Host name
Top Level Domain
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A Sample DNS Hierarchy
edu
Admin zones
virginia
unc
cs
ils
oit
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The Top level DNS hierarchy

• Originally included com, gov, edu, org, net
• Also country codes (doled out by IANA)
• ca canada
• au australia
• ch switzerland

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Name Resolution in DNS
Harrys computer
DNS Server
1. Resolve Name
Another explanation
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How do we find these servers and these locations?

• We can use our tools, such as
• whois
• traceroute

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Next session

• More client-server interactions

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so, lets practice some tools