Week 3 IP addressing

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Week 3 - IP addressing

• Introduction to IP addressing
• Classes of IP addressing
• Why Subnet Masks are necessary?
• How to create subnet masks

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Why are IP addresses written as bits?

• In order for data to pass along the media, it
  must first be changed to electrical impulses.
  
• When a computer receives these electrical
  impulses, it recognizes two things the presence
  of voltage on the wire or the absence of voltage
  on the wire.

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What format do IP addresses use?
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How are IP addresses expressed in dotted notation?
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Why are IP addresses necessary?

• IP addressing makes it possible for data passing
  over the network media of the Internet to find
  its destination.
  
• Because each IP address is a 32-bit value, that
  means that there are four billion different IP
  address possibilities.
  
• IP addresses are hierarchical addresses like
  phone numbers and zip codes.

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How do IP addresses make it possible for data
sent via the Internet to find its destination?

• It is because each network connected to the
  Internet has a unique network number.
  
• To ensure that each network number on the
  Internet will always be unique and unlike that of
  any other number, an organization called the
  International Network Information Center, or
  InterNIC

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How do IP addresses incorporate network
addresses?

• Every IP address has two parts. These are known
  as the network number and the host number.

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What are the different classes of networks?

• There are three classes of IP addresses that a
  company can receive from the InterNIC. The
  InterNIC reserves class "A" IP addresses for
  governments throughout the world, class "B" IP
  addresses for medium size companies, and class
  "C"

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What type of IP addressing format does a class
"A" network use?
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Class A
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Class B
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Class C
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How many classes of Networks are there?

• you have learned about three classes of networks
  that can be assigned by the InterNIC.
  
• In fact, there are five classes of networks.
  However, only three of these are used
  commercially.

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What IP addresses are reserved for multicast
purposes and experimental purposes?

• The highest number listed was 223. You may have
  wondered why the highest value was only 223 and
  not 255, since there are 255 possible values for
  an octet.
• in IP addresses the values 224 through 255 are
  not used in the first octet for networking
  purposes.

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What IP addresses are reserved for the Networks?

• By convention, in IP addressing schemes, any IP
  address that ends in all binary zeroes is
  reserved for the networkaddress.
  
• Thus, in a class "A" network, 113.0.0.0 would be
  the IP address of that network. Routers use a
  network's IP address when forwarding data on the
  Internet.

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What IP addresses are reserved for broadcasts?

• for the network that is 176.10.0.0, the broadcast
  address that would be sent out to all devices on
  that network would be 176.10.255.255.

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Who assigns subnet addresses?

• As with the host number portion of class "A,"
  class "B," and class "C addresses, subnet
  addresses are assigned locally.
  
• Usually this is done by the network administrator.

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What is included in a subnet address?

• Subnet addresses include a network number, a
  subnet number within the network, and a host
  number within the subnet.
  
• It is by providing this third level of addressing
  that subnets provide extra flexibility for the
  network administrator.

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How are subnet addresses created?

• To create a subnet address, a network
  administrator "borrows bits from the host field
  and designates them as the subnet field

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How are subnet addresses concealed from outside
networks?

• Subnets are hidden from outside networks by using
  a mask.
  
• These are referred to as subnet masks.
• The function of a subnet mask is to tell devices
  which part of an address is the network number
  including the subnet, and which part is the host.
  

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What format do subnet masks use?

• Subnet masks use the same format as IP
  addressing.
  
• In other words, they are thirty two bits long and
  divided into four octets.
  
• Subnet masks have all 1s in the network and
  subnetwork portion, and all 0s in the host
  portion.

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How many bits can be borrowed from the host
number in class "B" and class "C" networks to
create subnets?

• Because there are only two octets in the host
  field of a class "B network, up to fourteen bits
  can be borrowed to create subnetworks.
  
• A class "C" network has only one octet in the
  host field. Therefore, only up to six bits can be
  borrowed in class "C networks to create
  subnetworks.

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What happens to the subnet mask address if only
some of the bits in an octet are borrowed?

• Imagine that you have a class "B network. This
  time however, instead of borrowing all eight bits
  of the third octet, only seven bits are borrowed
  to create subnetworks.
• Using binary representation, in this example, the
  subnet mask would be 11111111.11111111.11111110.00
  000000.
  
• Therefore, 255.255.255.0 can no longer be used as
  the subnet mask.

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If only seven bits are borrowed in a class "B"
network, what would the subnet mask be in dotted
decimal notation?

• HINT To convert any eight bit binary number into
  a decimal number, total the powers of 2 that
  occur in the number.

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What determines how many subnetworks can be
created by borrowing bits from the host field?

• Can you figure out all of the possible
  combinations of 0s and 1s if four bits are
  borrowed from the host field to create
  subnetworks?
• 16 from 0000 to 1111. However, you know that 1111
  is reserved for broadcast and 0000 means this
  network.

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How many subnetworks can be created by borrowing
five bits from the host field?

• Answer Thirty-two subnetworks or 25 32
  subnetworks can be created by borrowing five
  bits from the host field.

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Which numbers in a subnetwork are reserved for
broadcasts?

• In previous section, we used an example of a
  class "C" network in which three bits are
  borrowed from the host field. You learned that
  when three bits are borrowed from the host octet,
  up to eight subnetworks can be created each
  having up to thirty-two hosts.
• You also learned that IP addresses ending in all
  binary 1s are reserved for broadcasts. The same
  is true for subnetworks.

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For IP address 197.15.22.160 on the same class
"C network. How would this be expressed in a
binary numbering scheme?

• Answer If 197.15.22.160 is converted to binary
  format, it becomes 110001010.00001111.00010110.
  10100000.
  
• The first three bits in the last octet, 101,
  indicate that this is the sixth subnetwork. As
  before the remaining bits are all binary 0s. This
  means that the IP address197.15.22.160 must be
  one that is reserved for a subnetwork address.

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How does the router handle IP addresses and
subnet masks?

• Let's assume that a device on another network
  with an IP address of 197.15.22.44 wants to send
  data to another device attached to Cisco's
  network with an IP address of 131.108.2.2.
• The data is sent out over the Internet until it
  reaches the router that is attached to Cisco's
  network.
  
• The router's job is to determine which one of
  Cisco's subnetworks the data should be routed to.
  
  

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when the router performs this ANDing" operation,
the host portion falls through.
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The router looks at what is left which is the
network number including the subnetwork.
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The router then looks in its routing table and
tries to match the network number including the
subnet with an interface.
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How does the "Anding operation change with
different subnet masks?

• Imagine that you have a class "B network with
  the network number 172.16.0.0.
  
• After assessing the needs of his network, the
  network administrator has decided to borrow eight
  bits in order to create subnetworks.
  
• When eight bits are borrowed to create subnets,
  the subnet mask is 255.255.255.0.
  
• Someone outside the network sends data to the IP
  address 172.16.2.120.

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