Networking

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Networking

• Chapter 7

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What is a network?

• Two or more computers interconnected so that
  information can be shared or transferred from one
  computer to another

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Common types of network (1)

• Broadcast
• Ethernet
• Any computer attached to the network can send a
  message anytime. Each system attached to the
  network examines the address in every message and
  picks up the message addressed to it.

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Common types of network (2)

• Token ring
• Fiber Distributed Data Interface (FDDI)
• Only one computer can send a message at any time.
  A token (special message) is constantly being
  passed around from one computer to another in the
  network. A computer can only send a message if
  it holds the token.

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Common types of network (3)

• Point-to-point
• Direct communication link from one computer to
  another

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LANs, WANs and MANs (1)

• LAN
• Local area network
• Ethernet, FDDI
• Small area small campus, building
• WAN
• Wide-area network
• Interconnects LANs
• Universities, research centers, corporations

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LANs, WANs and MANs (2)

• MAN
• Metropolitan area network
• Interconnects multiple LANs
• A large geographical area - city

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Typical Internetworking
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Network Protocols

• A protocol determines the format of network
  message packets
• UNIX systems typically use the TCP/IP protocol
• TCP/IP transport control protocol/internet
  protocol
• Highly reliable connection

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Host Addresses

• Host address
• Unique address of a computer in a network
• IP address
• 192.168.100.1
• 192.168 represent large network, perhaps one
  that is university-wide
• 100.1 represent a subnetwork, perhaps a
  department within a univeristy
• Network Information Center (NIC)
• The central authority that handles the assignment
  of addresses.
• Gives out block of addresses to organizations

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Symbolic Hostnames

• IP addresses are associated with host names that
  are easier to deal with
• 127.0.0.1 localhost
• 130.128.52.1 sobell.sro.com
• 130.128.52.2 bravo.sro.com
• 66.218.71.86 www.yahoo.com
• IP addresses are globally unique while hostnames
  are only unique locally within a LAN

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Domain Name Server (DNS)

• A special database that provides a mapping
  between IP addresses and hostnames

gov
com
edu
mil
org
net
sro
mma
berkeley
Level 1
okeeffe
sobell
bravo
okeeffe
Level 2

• The NIC assigns level 1 domain names. Individual
  systems administrator assigns names to individual
  machines at level 2.

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Communicating Over a Network in UNIX (1)

• Many commands applicable on a single computer
  have been extended to make them work over a
  network
• finger ? finger user_at_host
• talk ? talk user_at_host
• mail ? mail user_at_host

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Communicating Over a Network in UNIX (2)

• New UNIX utilities to control and monitor the
  network were created
• UNIX to UNIX connections
• rlogin, remote login
• rcp, remote copy
• UNIX to UNIX, UNIX to non-UNIX, non-UNIX to UNIX
  connections
• telnet, remote login
• ftp, file transfer

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Other Networking Features of UNIX

• USENET
• Formed in the early 1980s
• Loosely connected network of systems that
  exchange email and news items
• Internet Browsing
• archie server
• Similar in concept to search engine
• gopher client/server