8/26/2015CST Computer Networks1 CST 415

 Definitions  Internetworking  Internet Addressing  The Endians Revisited 8/26/2015CST Computer Networks2

Application Gateway Message level routing and forwarding is done by a layer of software integrated into the application itself. Network Level Interconnect Messages are delivered from source to destination without the intervention of any end user application programs.  decouples applications from network details.  Intermediate computers know nothing about end user applications.  Topology of networks is flexible.  Network technology can be upgraded without impacting end-to- end application interoperation. Internetworking Detaching application level communications from details of networking technologies and detaching networking technologies from physical transmission technologies. 8/26/2015CST Computer Networks3

 Provide an economical and fast media for transmission of information.  Provide communication between two arbitrary end points.  Insulate individual implementations from the system as a whole.  Provide a well defined and unified set of communication services.  Allow applications to be distributed across multiple computers in multiple locations. 8/26/2015CST Computer Networks4

Internetworking is controlled chaos where control is allowed because of careful specification and eventual standardization. The Internet grows unbounded with no global architect. Q: Is the Internet void of problems? Even the best laid plans of mice and men Often go astray And leave us nothing but grief and pain For promised joy - Robert Burns “To a Mouse” (paraphrased) 8/26/2015CST Computer Networks5

8/26/2015CST Computer Networks6 This is a fractal.

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Internetworking Explanation – From Stallings 1. See Stallings Figure 8 See Stallings Figure 8 2. See Stallings Figure 9 See Stallings Figure 9 3. See Stallings Figure 10 See Stallings Figure 10 8/26/2015CST Computer Networks8

 Internet addresses (IP addresses) are 32 bit addresses.  The bits are organized to optimize routing.  The address is split up into:  Net Identifier : Identify the network on which the host resides.  Host Identifier : Identify the host on the particular network. 8/26/2015CST Computer Networks9

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 Class A address  1 bit to identify the class (0 – class A, 1 – class B, C, D, or E)  7 bits for net ID : There can only be 128 of these in the world.  24 bits for host ID : Each network can have 16,777,216 host computers. 8/26/2015CST Computer Networks11

 Class B address  2 bits to identify the class (10 – class B, 11 – class C, D, or E)  14 bits for net ID : There can be 16,384 of these networks.  16 bits for host ID : Each network can have 65,536 host computers. 8/26/2015CST Computer Networks12

 Class C address  3 bits to identify the class (110 – class C, 111 – class D, or E)  21 bits for net ID : There can be 2,097,152 of these networks.  8 bits for host ID : Each network can have 254 host computers – 0 == network, 255 – IP Broadcast. 8/26/2015CST Computer Networks13

 Class D address Class D addresses are multicast addresses. 28 bits for these addresses – 268,435,456 addresses available. 8/26/2015CST Computer Networks14

 Class E address Class E addresses are reserved for future use and the bit structure has not yet been defined. 8/26/2015CST Computer Networks15

 Internet addresses do not address the host computer, they address the host-to-network connection.  Specify a host  Specify a computer  A host ID of all zeros is reserved to refer to the network.  A host ID of all ones is reserved for broadcast.  How can the address be used to specify broadcast on a specific network? 8/26/2015CST Computer Networks16

 The use of all zeros in an address field means “this”.  All zeros in a host field means “this” host.  All zeros in a network address means “this” network.  Can be used in the instance that a host does not know the network address.  Hopefully, any reply will have the full network address. 8/26/2015CST Computer Networks17

 Problems  Mobile host machines must be able to change their IP addresses.  What happens to a network when machine #256 needs to be added.  In packet routing, the route taken to a destination host is dependent on the netid.  More on these problems later. 8/26/2015CST Computer Networks18

Dotted Decimal Notation Address: is written: /26/2015CST Computer Networks19

Class Lowest Address Highest Address A B C D E The range of dotted decimal values that correspond to each IP address class. Some values are reserved for special purposes. 8/26/2015CST Computer Networks20

Loopback Address:  The loopback address allows the protocol stack to keep a packet destined for the local machine off the network.  This address can be used for inter-process communication using the TCP/IP protocol stack.  The address is  Using this address avoids propagating a packet onto the network hardware. 8/26/2015CST Computer Networks21

Reserved Private Addresses:  to  to  to and as of July 2001  to /26/2015CST Computer Networks22

The IANA (Internet Addressing Number Authority)  Administered by a single person “John Postel” until his death in 1998  After John died, an organization was formed to administer the addresses.  A new organization was defended to deal with this called ICANN (Internet Corporation for Assigned Names and Numbers)  The job of ICANN is to deal with the assignment of names and numbers in Internet addressing. 8/26/2015CST Computer Networks23

 Network byte order is “big endian”  largest byte in a multibyte item sent first  these bytes read naturally on a piece of paper : left to right.  big-endian is basically every processor type but Intel.  Intel processors are little endian (least significant byte first)  Intel processors must swap bytes when reading data from a standard network connection. 8/26/2015CST Computer Networks24