INP 150: Internet Technology

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INP 150 Internet Technology

• Class 4 Domain Names and IP Addresses

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Objectives

• What is the DNS (Domain Name System)?
• How does the DNS work?
• What is the whois database?
• What are some commonly seen domain names?
• Describe current efforts to expand the IP address
  space.
• What is a URL?
• What are a URLs components?

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Reading

• Make sure you read How Domain Name Servers Work
• linked to syllabus
• very gentle yet thorough explanation of DNS

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Student Question What is a T1 Connection?

• Standard for digital (not analog) transmission
• Twisted-pair wiring, fiber optic
• 24 channels, each with 64 Kbps (voice or data)
• Total of 1.544 Mbps
• Links together networks
• T3 used for Internet backbone
• 44.746 Mbps
• 28 T1 lines

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http//www.utelsystems.com/images/y-cable-large.jp
g
http//www.apacn.com/images-apacn/T1_CABLE.JPG
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What is an IP address?

• 32-bit number
• xxx.xxx.xxx.xxx
• each octet has the range of 28, or 0-255
• 1 byte 8 bits, which can hold 28 values
• 255.255.255.255
• 127.0.0.1 is reserved as localhost
• Refers to the actual computer you are using
• Every computer connected to the Internet is
  assigned an IP address!
• Static IP address
• Dynamic IP address

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Finding an IP address

• Unix
• Type host http//host.domain.name
• Dos (WinXP)
• IPCONFIG.EXE
• Online
• http//www.hcidata.co.uk/host2ip.htm

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What is an IP range?

• E.g., MIT's includes
• 128.30..
• How many IP addresses is this?
• MIT also has 198.125.176.-19.125-179.
• A domain range is the range of IP addresses in a
  specific network!

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DNS

• Domain Name Servers
• One of the largest distributed databases in the
  world
• Billions of queries a day
• Translates URL into IP address
• Need IP address to route packets
• But its easier to remember a URL than an IP
  address

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Why is it distributed?

• DNS is far too complex for just one database
• Too many hits
• Overwhelm the processor
• Too many addresses
• The database table would take forever to query!
• Too much to administrate
• IP addresses are changed and added daily
• All said and done, it has to be distributed!

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How does the DNS work?

• Many DNS databases
• When you make a query, your browser goes to a DNS
  
• You can actually select a DNS
• If the DNS knows the IP address, it will give you
  the IP address
• What if it doesn't know
• Contacts a root DNS database
• Roots know where a DNS database is that can
  translate a particular IP
• Remember, IP addresses are hierarchical

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DNS databases cache!

• When a DNS doesn't know
• Contact DNS root database that asks the right DNS
  database
• That DNS database tells the root, which tells the
  first DNS database the IP address
• Then, that DNS database caches the IP address
• Cache means to temporarily store
• Make the DNS system more efficient
• Common queries aren't made over and over again
• Time-to-live (TTL)

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Whois Database

• Network Solutions keeps track of who owns what
  domains
• This is a database called the whois database
• Can view it online!
• Makes sure that domain names are unique!
• Also gives contact information so you can make an
  offer on a domain

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Visit the whois database

• http//www.networksolutions.com/en_US/whois/index.
  jhtml

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URLs

• URL Uniform Resource Locators
• Pronounced Earl
• E.g., http//courses.wccnet.edu/
• Made up of a host name, second-level name, and a
  top-level name
• http//host_name.second.top

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Host Name

• Specifies which machine in a network holds a
  particular server
• Most common is www
• E.g., www, telnet, courses, stu, mail, etc.
• These are arbitrary!
• A DNS helps unravel which machine has which IP
  address
• There are text-files that say which machines have
  which server names!

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Example of Host Name Config

• This file tells the DNS
• How many servers
• IP addresses for servers
• What the servers are called
• The host name is www

http//computer.howstuffworks.com/dns6.htm
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Top-level Domain Name

• Top-level domain names tell what type of
  organization owns the site
• com
• edu
• gov
• mil
• net
• org
• us
• uk
• jp
• Hundreds of top-level domain names

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Domain Names

• Combination of second-level name and top-level
  name
• e.g., wccnet.edu and wccnet.org are two
  different domain names
• If you purchase a domain name, you may buy
  several domain names
• name.com
• name.org
• name.net

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Parked Domains

• You can hold on to more than one domain
• www.yahoo.com
• www.yahoo.org
• yahoo.org refers to yahoo.com
• This is called a parked domain

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Companies DNS

• Many companies (and large organizations) have
  their own DNS
• Can manage their IP range and handle requests to
  different servers in their networks
• Makes the web more efficient
• Makes accessing and administrating a complex
  network with many servers easier

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IP address space

• Currently using Ipv4
• 4 octets
• 2554 IP addresses, or 3,544,535,296 addresses
• There are a limited number of addresses
• As a result, addresses are now rented out instead
  of owned
• There used to be a class system
• B/c this class system is no longer used, we don't
  have to learn it!

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Running out of IP addresses!

• We are running out of IP addresses... what can we
  do?
• We can subdivide networks
• However, this means that routing tables would
  become more complex
• This means that search time would increase
  dramatically
• Still doesn't solve the problem that there are a
  limited number of IP address

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IPv6

• Ipv6 uses 6 octets
• xxx.xxx.xxx.xxx.xxx.xxx
• 2568, or 281,474,976,710,656 different IP
  addresses!
• Means a new implementation
• Have to change routers, DNS, a host operating
  systems!
• Quite a task, but some networks have already
  started the switch

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Review

• What is the DNS (Domain Name System)?
• How does the DNS work?
• What is the whois database?
• What are some commonly seen domain names?
• Describe current efforts to expand the IP address
  space.
• What is a URL?
• What are a URLs components?

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Hacking a Misnomer

• The popular media misused the term hacker
• Frequently misused to refer to someone who
  hacks into another computer
• Better name is cracker
• The person can use a port scanner and an IP
  address to find a way into another computer!

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Cracking and IP Address How-to

• First, you need an IP address
• Multiple ways to get one... create scripts
• For web servers, you can locate IP addresses very
  easily
• Next, you use a port scanner on the IP address
• Find an open port
• Firewalls protect you from crackers
• With an open port and an IP address, you can
  create a script that navigates and takes control
  of another computers filesystem.

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Honey pots

• Lot's of script kiddies try this out
• And go to jail...
• Sometimes, administrators trick a cracker
• Leave a port open
• Watch for activity, notify policy or FBI
• This is called a honey pot
• Moral don't use port scanners on other people's
  computers