04/20/23 CST 415 - Computer Networks 1

CST 415

Definitions Internetworking Internet Addressing The Endians Revisited

04/20/23 CST 415 - Computer Networks 2

Application GatewayMessage level routing and forwarding is done by a layer

of software integrated into the application itself.

Network Level InterconnectMessages 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.

InternetworkingDetaching application level communications from details

of networking technologies and detaching networking technologies from physical transmission technologies.

04/20/23 CST 415 - Computer Networks 3

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.

04/20/23 CST 415 - Computer Networks 4

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 menOften go astrayAnd leave us nothing but grief and painFor promised joy

- Robert Burns “To a Mouse” (paraphrased)

04/20/23 CST 415 - Computer Networks 5

04/20/23 CST 415 - Computer Networks 6

This is a fractal.

04/20/23 CST 415 - Computer Networks 7

Internetworking Explanation – From Stallings

1. See Stallings Figure 82. See Stallings Figure 93. See Stallings Figure 10

04/20/23 CST 415 - Computer Networks 8

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.

04/20/23 CST 415 - Computer Networks 9

04/20/23 CST 415 - Computer Networks 10

Class A address1 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.

04/20/23 CST 415 - Computer Networks 11

Class B address2 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.

04/20/23 CST 415 - Computer Networks 12

Class C address3 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.

04/20/23 CST 415 - Computer Networks 13

Class D address

Class D addresses are multicast addresses.

28 bits for these addresses – 268,435,456 addresses available.

04/20/23 CST 415 - Computer Networks 14

Class E address

Class E addresses are reserved for future use and the bit structure has not yet been defined.

04/20/23 CST 415 - Computer Networks 15

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?

04/20/23 CST 415 - Computer Networks 16

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.04/20/23 CST 415 - Computer Networks 17

ProblemsMobile 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.04/20/23 CST 415 - Computer Networks 18

Dotted Decimal Notation

Address:10000000 00001010 00000010

00011110

is written:128.10.2.30

04/20/23 CST 415 - Computer Networks 19

Class Lowest Address Highest Address

A 1 . 0 . 0 . 0 126 . 0 . 0 . 0B 128 . 1 . 0 . 0 191 . 255 . 0 . 0C 192 . 0 . 1 . 0 223 . 255 . 255 . 0D 224 . 0 . 0 . 0 239 . 255 . 255 .

255E 240 . 0 . 0 . 0 255 . 255 . 255 .

254

The range of dotted decimal values that correspond to each IP address class. Some values are reserved for special purposes.

04/20/23 CST 415 - Computer Networks 20

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 127.0.0.1 Using this address avoids propagating a

packet onto the network hardware.

04/20/23 CST 415 - Computer Networks 21

Reserved Private Addresses: 10.0.0.0 to 10.255.255.255 172.16.0.0 to 172.31.255.255 192.168.0.0 to 192.168.255.255

and as of July 2001 169.254.0.0 to 169.254.255.255 

04/20/23 CST 415 - Computer Networks 22

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.

04/20/23 CST 415 - Computer Networks 23

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.

04/20/23 CST 415 - Computer Networks 24