Bellevue University

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Bellevue University

• CIS 351
• OSI and TCP/IP

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Topics

• Comparison of OSI and TCP/IP Models
• Local Area Networking using Ethernet and TCP/IP
• Ethernet
• The TCP/IP Protocol Stack

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The OSI Reference Model
Application
Presentation
Session
Transport
Network
Data Link
Physical
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TCP/IP

• Development was funded by US Governments
  Advanced Research Projects Agency (ARPA) in 1960s
  and 1970s.
• Widely used protocol suite Protocol of choice
  for the Internet and most operating systems
• Implementation parallels the OSI Model

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The TCP/IP Model
Application
Transport
Internet
Network Interface
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TCP/IP Protocol Suite

• Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)
• Internet Protocol (IP)
• Internet Control Message Protocol (ICMP)
• Internet Group Management Protocol (IGMP)
• Address Resolution Protocol (ARP)
• TCP/IP Utilities

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TCP/IP Layers
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Ethernet

• Covers both Physical and Data link standards in
  ISO model
• Covers
• Uses CSMA/CD
• Handles communication at the link level
• Sends and receives frames

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Ethernet (cont)

• IEEE 802.3 Carrier Sense Multiple Access
  with Collision Detection (CSMA/CD) Access Method
  and Physical Layer Specifications
• Physical layer specification
• Frame Format
• CSMA/CD Media Access Control (MAC) mechanism

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Physical Layer

• Star or bus topology
• RG8 or RG58 Coax, UTP, STP, or fiber optic cable
• Coax limited to 10 MBps
• UTP, STP, and fiber optic limited to 1GBps
  (currently)

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100BaseT

• Most popular physical layer for Ethernet LANs
• Category 5 Unshielded Twisted Pair cable
• RJ-45 Connectors
• Star Topology - requires a hub or switch

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Cat 5 UTP
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Cable Connections
Pin Color NIC Hub or Switch
1 Striped Orange Tx Rx
2 Solid Orange Tx Return Rx Return
3 Striped Green Rx Tx
4 Solid Blue Not Used Not Used
5 Striped Blue Not Used Not Used
6 Solid Green Rx Return Tx Return
7 Striped Brown Not Used Not Used
8 Solid Brown Not Used Not Used
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The 5-4-3 Rule

• You may have five cable segments
• Connected by four repeaters
• No more than three segments can be of mixed types

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Packet Terminology

• Segment

• Message

• Datagram

• Frame

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TCP/IP Traffic From top to bottom
segment
Application layer data
message
Application layer data
TCP header
datagram
Transport layer data
IP header
frame
Internet layer data
Ethernet header
Ethernet footer
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Ethernet Frame
Preamble
Start of Frame Delimiter
Destination Address
Source Address
Ethertype/Length
Data and Pad
Frame Check Sequence
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Preamble

• 7 bytes of alternating ones and zeros used to
  synchronize clock signals with the incoming frame

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Start of Frame Delimiter

• A one byte field consisting of 6 ones and zeros
  followed by two consecutive ones. The ones
  signal that the bits to follow contain the start
  of the actual frame

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Destination Address

• A six byte field containing the hardware address
  of the destination end of the link

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Source Address

• A six byte field containing the address of the
  network interface adapter that generated the
  packet.

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Addressing

• Six byte hardware address
• Unique to each Network Interface Card
• Consists of a three byte Organizationally Unique
  Identifier and three byte serial number

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Organizationally Unique Identifier (OUI)

• First three bytes of the hardware address
• Identifies the company that manufactured the
  Network Interface
• Complete list can be found at
• http//standards.ieee.org/regauth/oui/oui.txt

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Example

• 00-10-5A (hex) 3COM CORPORATION 00105A (base
  16) 3COM CORPORATION 5400 BAYFRONT PLAZA
  MAILSTOP 4220 SANTA CLARA CA 95052 UNITED STATES

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Ethertype/Length

• Contains the protocol type and length of the
  data field excluding any pad

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Common Ethertype Values

• 0800 Internet Protocol
• 0805 X.25
• 0806 ARP
• 8035 RARP
• 809B AppleTalk on Ethernet
• 8137 Netware IPX

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Data and Pad

• Contains the data passed down from the network
  layer protocol on the transmitting system
• Padding is used if the length of the data sent
  from the network layer is less than 46 bytes.
• The maximum length for the data field is 1500
  bytes

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Frame Check Sequence

• Four bytes of footer that contain a checksum of
  the entire packet.
• The transmitting computer calculates the checksum
  and stores it in the footer.
• The receiving computer recalculates the checksum
  and compares it to the stored checksum.
• Transmission is successful if both checksum
  values match

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Internet Protocol (IP)
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Datagram (IP)
Version
IHL
Total Length
Type of Service
Identification
Flags
Fragment Offset
Time To Live
Protocol
Header Checksum
Source IP Address
IP Header
Destination IP Address
Options
Data
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Some Common Protocol Numbers (RFC 791)

• 1 ICMP
• 2 IGMP
• 6 TCP
• 17 UDP

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IP Addressing

• Uses a 32 bit binary address
• Address is expressed as group of four decimal
  numbers in the range of 0-255, separated by
  periods (also known as dots)

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Classful IP Addressing

• IP Addresses
• IP Address Classes

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IP Address Classes
Class A
Network ID
Host ID
Class B
Network ID
Host ID
Class C
Network ID
Host ID
w
x
y
z
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Limitations of the Original IP Addressing Scheme
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Solution Classless Inter-Domain Routing (CIDR)
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The Key to CIDR is the Subnet Mask

• Subnet Mask Bits
• CIDR Notation
• Calculating the Network ID
• Determining Local and Remote Hosts

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Subnet Masks

• Determine which part of the IP address is the
  Network part and which is the host part
• Example
• 255.0.0.0

Network
Host
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Subnet Mask Bits
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Using CIDR Notation to indicate the configuration
of the subnet mask
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Calculating the Network ID
IP Address in CIDR Notation 10.217.123.7/20
IP Address
10 . 217 . 123 . 7
00001010 11011001 01111011 00000111
Subnet Mask
255 . 255 . 240 . 0
11111111 11111111 11110000 00000000
Network ID
00001010 11011001 01110000 00000000
Network ID in CIDR Notation
10.217.112.0/20
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IP Address Classes

• Class A 0x.x.x.x
• Class B 10x.x.x.x
• Class C 110x.x.x.x
• Class D 1110x.x.x.x

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Private Addresses(Non-routable over the Internet)

• 10.x.x.x Class A private IPs
• 172.(16-31).x.x Class B private IPs
• 192.168.x.x Class C private IPs
• 169.254.x.x Automatic Private IP (Microsoft)

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Internet Control Message Protocol (ICMP)
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ICMP

• Network layer TCP/IP Protocol
• Described in RFC 792
• Carries informational queries and error messages
• Used by the ping command

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Internet Group Management Protocol (IGMP)
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IGMP

• Network layer TCP/IP Protocol
• Described in RFC 2236
• Provides a way for an Internet computer to report
  its multicast group membership to adjacent
  routers

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Address Resolution Protocol (ARP)
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Transmission Control Protocol (TCP)
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TCP

• Connection oriented
• Transport layer protocol
• Uses port numbers
• Handles segments

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Message (TCP)
Source IP Address
Pseudo- Header
Destination IP Address
Unused
Protocol
Length
Source Port
Destination Port
Sequence Number
Acknowledgement Number
TCP Header
Data Offset
Reserved
Control Bits
Window
Checksum
Urgent Pointer
Options
Data
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Port numbers

• A unique number that relates to a service or
  protocol
• Assigned by the Internet Assigned Numbers
  Authority (IANA) and published in RFC 1700
• Contained in a file called SERVICES

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Source Port

• 2 Bytes in length
• Identifies the process on the transmitting system
  that generated the information in the Data field

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Destination Port

• 2 Bytes in length
• Identifies the process on the receiving system
  for which the information in the Data field is
  intended

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Sequence Number

• 4 bytes
• Unique number that identifies the location of the
  data in this segment in relation to the entire
  sequence.

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Acknowledgment

• Used for acknowledgment messages
• Specifies the sequence number of the next segment
  expected by the receiving system

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Data Offset

• 4 Bits in length
• Specifies the number of 4 byte words in the TCO
  header

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Reserved

• 6 Bits in length
• This field is not used

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Control Bits

• 6 bits in length
• URG set if segment contains urgent data
• ACK set if acknowledgment message
• PSH set to forward immediately
• RST set to reset TCP configuration and discard
  all segments
• SYN set to synchronize sequence numbers
• FIN set to terminate a TCP connection

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Window

• 2 Bytes in length.
• Specifies how many bytes the computer is capable
  of accepting from the connected system.

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Checksum

• 2 Bytes in length
• Contains the result of a cyclical redundancy
  check (CRC) performed by the transmitting system
• The CRC is recalculated at the receiving end and
  compared with the number in the checksum field

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Urgent Pointer

• 2 Bytes in length
• When the urgent (URG) control bit is present,
  this field indicates which part of the data in
  the segment is urgent

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Options

• Variable length field
• Contains information related to optional TCP
  connection configuration features.

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Socket

• Composed of an IP address and TCP port number
• Example 216.115.102.7980

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User Datagram Protocol (UDP)
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Identifying Applications
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TCP/IP Utilities
Ftp
Connectivity Utilities
Diagnostic Utilities
Telnet
Tftp
TCP/IP Printing Service
Server-based Software
Internet Information Services
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Data Flow
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The TCP/IP Model
Sender
Receiver
Application
Transport
Internet
Network Access
Application
Transport
Internet
Network Access
TCP
IP
IP
MAC
MAC
Router
Data link
Data link