Ip Networks and Tcp-ip Iipntip001

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1IP Networks & TCP-IP

IP NETWORKS AND TCP-IP

MODULE ID: IIPNTIP001

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Topics Covered

1. Networks - LAN / WAN2. TCP-IP Introduction3. Comparison with DoD Model4. TCP-IP Protocol Suite5. TCP & UDP6. Inter Net Layer Protocols (IP)7. IP Addresses8. Classes and Subnets9. Private IP Addresses and NAT

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Networks

LAN 1 LAN 2

WAN

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Local Area Networks (LANs)

LANs are designed to: Operate within a limited geographical area Allow multi access to high bandwidth media Control of network privately under local

administration Provide full time connectivity to local services Connect physically adjacent devices

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Devices used

Repeaters Hubs Bridges Switches Routers Links (cables & connectors)

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Wide Area Networks (WANs)

WANs are designed to: Operate over large geographical area Allow access over serial interfaces operating

at low speeds Provide full time & part time connectivity

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Devices used in WAN

Routers

Modems

Links

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Network Topology

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Importance of Bandwidth

Bandwidth is data transmission rate The maximum amount of information

(bits/second) that can be transmitted along a channel

It is limited by physics and technology It is critical to network performance

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TCP/IP and the DoD Model

The Transmission Control Protocol / Internet Protocol (TCP/IP) suite was created by the Department of Defense (DoD) to ensure and preserve data integrity, as well as maintain communications in the event of catastrophic war

If designed and implemented correctly, a TCP/IP network can be a truly dependable and resilient one.

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The DoD model is basically a condensed version of the OSI model It is composed of four, instead of seven, layers: Process/Application layer Host-to-Host layer Internet layer Network Access layer

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The DoD and OSI models

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A no. of protocols combine at the DoD models Process/Application layer to integrate the various activities and duties spanning the focus of the OSIs corresponding top three layers (Application, Presentation, and Session)

The Process/Application layer defines protocols for node-to-node application communication and also controls user-interface specifications

The Host-to-Host layer parallels the functions of the OSIs Transport layer, defining protocols for setting up the level of transmission service for applications

It tackles issues such as creating reliable end-to-end communication and ensuring the error-free delivery of data

It handles packet sequencing and maintains data integrity.

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The Internet layer corresponds to the OSIs Network layer, designating the protocols relating to the logical transmission of packets over the entire network

It takes care of the addressing of hosts by giving them an IP (Internet Protocol) address, and it handles the routing of packets

The Network Access layer monitors the data exchange between the host and the network

The equivalent of the Data Link and Physical layers of the OSI model, the Network Access layer oversees hardware addressing and defines protocols for the physical transmission of data.

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The TCP/IP protocol suite

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The Process/Application Layer Protocols

Telnet

FTP

TFTP

NFS

SMTP

LPD X Window

SNMP

DNS

DHCP/BootP

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The Host-to-Host Layer Protocols

The main purpose of the Host-to-Host layer is to shield the upper-layer applications from the complexities of the network.

The two protocols at this layer: Transmission Control Protocol (TCP) User Datagram Protocol (UDP)

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Transmission Control Protocol (TCP)

Transmission Control Protocol (TCP) takes large blocks of information from an application and breaks them into segments.

It numbers and sequences each segment so that the destinations TCP protocol can put the segments back into the order the application intended.

After these segments are sent, TCP (on the transmitting host) waits for an acknowledgement of the receiving ends TCP virtual circuit session, retransmitting those that arent acknowledged.

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Before a transmitting host starts to send segments, the senders TCP protocol contacts the destinations TCP protocol to establish a connection.

What is created is known as a virtual circuit This type of communication is called connection-

oriented During this initial handshake, the two TCP layers also

agree on the amount of information thats going to be sent before the recipients TCP sends back an acknowledgement

Transmission Control Protocol (TCP)

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TCP Segment Format

The upper layers just send a data stream to the protocols in the Transport layers,

TCP segments a data stream and prepares it for the Internet layer.

The Internet layer then routes the segments as packets through an internetwork.

The segments are handed to the receiving hosts Host-to-Host layer protocol, which rebuilds the data stream to hand to the upper-layer applications or protocols.

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TCP segment format

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TCP Segment Format

The TCP header is 20 bytes long, or up to 24 bytes with options.

The TCP segment contains the following fields: Source port :The port number of the application on

the host sending the data. Destination port: The port number of the application

requested on the destination host. Sequence number Puts the data back in the correct

order or retransmits missing or damaged data, a process called sequencing.

Acknowledgement number Defines which TCP octet is expected next.

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TCP Segment Format

Header length :The number of 32-bit words in the TCP header. This indicates where the data begins. The TCP header (even one including options) is an integral number of 32 bits in length.

Reserved Always set to zero. Code bits: Control functions used to set up and

terminate a session. Window :The window size the sender is willing to

accept, in octets. Checksum: The cyclic redundancy check (CRC),

because TCP doesnt trust the lower layers and checks everything. The CRC checks the header and data fields.

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TCP Segment Format Urgent: A valid field only if the Urgent pointer in the code

bits is set. If so, this value indicates the offset from the current sequence number, in octets, where the first segment of non-urgent data begins.

Options: May be 0 or a multiple of 32 bits, if any. What this means is that no options have to be present (option size of 0).

if any options are used that do not cause the option field to total a multiple of 32 bits, padding of 0s must be used to make sure the data begins on a 32-bit boundary.

Data Handed down to the TCP protocol at the Transport layer, which includes the upper layer headers.

TCP creates a lot of overhead. Application developers may opt for efficiency over reliability

to save overhead, so User Datagram Protocol was also defined at the Transport layer as an alternative.

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TCP Connection EstablishmentHost A sends a TCP SYNchronize packet to Host B

Host B receives A's SYN

Host B sends a SYNchronize-ACKnowledgement

Host A receives B's SYN-ACK

Host A sends ACKnowledge

Host B receives ACK.

TCP socket connection is ESTABLISHED

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TCP Three WAY Handshake

HOST A HOST B

TIME IN THE NETWORK

Send SYN Seq=x Receive SYN

Send SYN seq=y ACK=x+1

Receive SYN+ACKSend ACK=y+1

Receive ACK

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TCP Connection TerminationThe client TCP sends the FIN segment first.

The server TCP sends the ACK segment to confirm the receipt of the FIN from the client.

It increments the sequence number of FIN by 1 and no other user data will add with the ACK segment.

Server does not have any data for transmission, and then it sends the FIN segment to Client side.

Then client sends the ACK segment again to the server side. The connection termination fulfilled.

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TCP 4 WAY TerminationHOST A HOST B

TIMEIN THE NETWORK

Established Connection

Close WaitPassive Close

Last ACK

Closed

Established Connection

Active Close Fin-Wait 1

Fin-Wait 2

Time Wait

Closed

FIN

ACK

FIN

ACK

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User Datagram Protocol (UDP)

UDP is covered thoroughly in Request for Comments 768. The Requests for Comments (RFCs) form a series of notes,

started in 1969,about the Internet UDP is preferred over TCP when reliability is already

handled at the Process/Application layer. UDP does not sequence the segments and does not care in

which order the segments arrive at the destination. UDP sends the segments off and forgets about them. It doesnt follow through, check up on them, or even allow

for an acknowledgment of safe arrival. Because of this, its referred to as an unreliable protocol. This does not mean that UDP is ineffective, only that it

doesnt handle issues of reliability.

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UDP doesnt create a virtual circuit, nor does it contact the destination before delivering information to it.

Because of this, its also considered a connectionless protocol.

Since UDP assumes that the application will use its own reliability method, it doesnt use any.

This gives an application developer a choice when running the Internet Protocol stack: TCP for reliability or UDP for faster transfers.

User Datagram Protocol (UDP)

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UDP Segment Format

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UDP Segment Format

The UDP segment contains the following fields: Source Port: Port number of the application on the

host sending the data. Destination Port: Port number of the application

requested on the destination host. Length: Length of UDP header and UDP data. Checksum: Checksum of both the UDP header

and UDP data fields. Data Upper-layer data.

UDP, like TCP, doesnt trust the lower layers and runs its own CRC. Frame Check Sequence (FCS) is the field that houses the CRC

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Key Features of TCP and UDP

TCP UDP

Sequenced Unsequenced

Reliable Unreliable

Connection-oriented Connectionless

Virtual Circuit Low overhead

Acknowledgments No Acknowledgments

Windowing Flow Control No Windowing Flow Control

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Port Numbers

TCP and UDP must use port numbers to communicate with the upper layers, because they keeps track of different conversations crossing the network simultaneously.

Originating source port numbers are dynamically assigned by the source host and will equal some number starting at 1024.

Virtual circuits that dont use an application with a well-known port number are assigned port numbers randomly from a specific range

These port numbers identify the source and destination application or process in the TCP segment.

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Numbers below 1024 are considered well-known port numbers and are defined in RFC 3232.

Numbers 1024 and above are used by the upper layers to set up sessions with other hosts, and by TCP to use as source and destination addresses in the TCP segment.

Port Numbers

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Port numbers for TCP and UDP

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Port Numbers

Why does the source host make up a port number? To differentiate between sessions with different hostsHow else would a server know where information is coming from if it didnt have a different number from a sending host?TCP, UDP and the upper layers dont use hardware and logical addresses to understand the sending hosts address as the Data Link and Network layer protocols do. They use port numbers.

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Key Protocols That Use TCP and UDP

TCP UDPftp 21 dns 53ssh 22 tftp 69

telnet 23 snmp 161smtp 25dns 53http 80

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The Internet Layer Protocols

There are two main reasons for the Internet layers existence: routing, and providing a single network interface to the upper layers.

The following are the protocols at the Internet layer: Internet Protocol (IP) Internet Control Message Protocol (ICMP) Internet Group Management Protocol (IGMP) Address Resolution Protocol (ARP) Reverse Address Resolution Protocol (RARP) Proxy ARP

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Internet Protocol (IP)IP looks at each packets address. Then, using a routing table, it decides where a packet is to be sent next, choosing the best path.The protocols of the Network Access layer deal only with physical links (local networks).Identifying devices on networks requires answering these two questions: Which network is it on? And What is its ID on that network? The first answer is the software address, or logical address The second answer is the hardware address All hosts on a network have a logical ID called an IP address. This is the software, or logical, address and contains valuable encoded information, greatly simplifying the complex task of routing.

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Internet Protocol (IP)

IP receives segments from the Host-to-Host layer and fragments them into datagrams (packets) if necessary.

IP then reassembles datagrams back into segments on the receiving side.

Each datagram is assigned the IP address of the sender and of the recipient.

Each router (layer 3 device) that receives a datagram makes routing decisions based on the packets destination IP address.

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IP Header

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IP Header

The following fields make up the IP header: Version: IP version number. Header Length: Header length (HLEN) in 32-bit words. ToS with IP Precedence Bits: Type of Service tells how

the datagram should be handled. The first 3 bits are the priority bits. Total length: Length of the packet including header and

data. Identifier Unique IP-packet value. Flags: Specifies whether fragmentation should occur. Fragment offset: Provides fragmentation and

reassembly if the packet is too large to put in a frame. It also allows different maximum transmission units

(MTUs) on the Internet.

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IP Header TTL The time to live (TTL) is set into a packet when it is

originally generated. If it doesnt get to where it wants to go before the TTL expires, boomits gone. This stops IP packets from continuously circling the network looking for a home.

Protocol Port of upper-layer protocol (TCP is port 6 or UDP is port 17 [hex]). Also supports Network layer protocols.

Header checksum: Cyclic redundancy check (CRC) on header only.

Source IP address :32-bit IP address of sending station. Destination IP address: 32-bit IP address of the station

this packet is destined for. IP options Used for network testing, debugging, security,

and more. Data After the IP option field will be the upper-layer data

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The Protocol field in an IP header

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Possible Protocols Found in the Protocol Field of an IP Header

Protocol Protocol NumberICMP 1IGRP 9

EIGRP 88OSPF 89IPv6 41GRE 47

IPX in IP 111Layer 2 Tunnel (L2TP) 115

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Internet Control Message Protocol (ICMP)

Internet Control Message Protocol (ICMP) works at the Network layer and is used by IP for many different services.

ICMP is a management protocol and messaging service provider for IP.

Its messages are carried as IP data-grams.

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Internet Control Message Protocol (ICMP)

Some common events and messages that ICMP relates to: Destination Unreachable Buffer Full Hops Ping Traceroute

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Address Resolution Protocol (ARP)

Address Resolution Protocol (ARP) finds the hardware address of a host from a known IP address.

When IP has a datagram to send, it must inform a Network Access protocol, such as Ethernet or Token Ring, of the destinations hardware address on the local network.

If IP doesnt find the destination hosts hardware address in the ARP cache, it uses ARP to find this information.

ARP interrogates the local network by sending out a broadcast asking the machine with the specified IP address to reply with its hardware address.

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Reverse Address Resolution Protocol (RARP)

When an IP machine happens to be a diskless machine, it has no way of initially knowing its IP address

But it does know its MAC address Reverse Address Resolution Protocol (RARP)

discovers the identity of the IP address for diskless machines by sending out a packet that includes its MAC address and a request for the IP address assigned to that MAC address.

A RARP server, responds with the answer, and the identity is given

RARP uses the information it does know about the machines MAC address to learn its IP address

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Local ARP broadcast

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RARP broadcast example

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IP Addressing

Internet Protocol (IP) A unique identifier for host, on an IP network 32-bit binary number, usually expressed as 4

dotted decimal values. Each decimal value represents 8 bits, in the

range of 0 to 255

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Example of IP Address

We see the address in the decimal formOur computer sees it in the binary form

140.179.220.200

Written in binary form:

140. 179. 220. 200

10001100.10110011.11011100.11001000

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(32 Bit Address 2^32 = 4.3 billion possible addresses) There are 5 different address classes. Only 3 are in commercial use at this time. You can determine the class of the address by looking

at the first 4 bits of the IP address: Class A begin with 0xxx, or 1 to 126 decimal Class B begin with 10xx, or 128 to 191 decimal Class C begin with 110x, or 192 to 223 decimal Class D begin with 1110, or 224 to 239 decimal Class E begin with 1111, or 240 to 254 decimal

Address Classes

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Network vs. Host

Every IP address has 2 parts: One identifying the network it resides on Other identifying the host address on the

network The class of the address and the subnet mask

determine which part belongs to the network address and which part belongs to the host address

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IP Address Components

The class of the address determines, by default, which part is for the network (N) and which part belongs to the host (H)

Class A: NNNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHHH Class B: NNNNNNNN.NNNNNNNN.HHHHHHHH.HHHHHHHH Class C: NNNNNNNN.NNNNNNNN.NNNNNNNN.HHHHHHHH

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IP Address Components - Eg

Our example is a Class B address 140.179.220.200 By default, the Network part of the address is defined

by the first 2 octets: 140.179.x.x

By default, the Host part of the address is defined by the last 2 octets: x.x.220.200

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Two Reserved Addresses on a Subnet

In order to specify the Network Address of a given IP address, the Host portion is set to all 0s: 140.179.0.0

If all the bits in the Host portion are set to 1s, then this specifies the broadcast address that is sent to all hosts on the network: 140.179.255.255

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Subnet Mask

Subnet masks are applied to an IP address to identify Network portion and Host portion of the address.

Computer performs a bitwise logical AND operation between the address and the subnet mask in order to find the Network Address or number.

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Default Subnet Masks

Class A - 255.0.0.011111111.00000000.00000000.00000000

Class B - 255.255.0.011111111.11111111.00000000.00000000

Class C - 255.255.255.011111111.11111111.11111111.00000000

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Logical Bitwise AND Operation

140.179.220.200 Class B address255.255.0.0 Subnet Mask

In Binary:

10001100.10110011.11110000.1100100011111111.11111111.00000000.0000000010001100.10110011.00000000.00000000

By doing this, the computer has found that our Network Address is 140.179.0.0

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IP Addressing Methods

Static Address

Manually entered addresses

Dynamic Address

Allocated from a pool of Addresses by DHCP

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Private IP Addresses

You can use these addresses on any private LAN.

You CANNOT use them on the internet. Internet routers will block them. Class A10.0.0.0 - 10.255.255.255 Class B172.16.0.0 - 172.31.255.255 Class C192.168.0.0 - 192.168.255.255

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Network Address Translation

Packets with Private IP addresses cannot not be routed on a public network

NAT maps the private IP addresses on a home network to the public IP addresses which is the IP address supplied by an Internet Service Provider (ISP)

NATing is done at the boundary of the private network (LAN)

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Summary

TCP-IP is based on DoD Model There are various protocols in TCP-IP

Protocol Suite TCP is reliable but UDP is not reliable Port No.s identify source and destination

application IP is a Internet layer Protocol IP address is 32 bit in size These are 3 Classes for commercial use In each class some range of IP addresses are

reserved for Private use

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References

Books: TCP/IP ILLUSTRATED -W.RICHARD

STEVENS INSIDE TCP/IP - KRANJIT S. SIYAN CCNA Cisco certified network associate - T.

Lammle URLs: http://en.wikipedia.org http://cisco.com

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Ip Networks and Tcp-ip Iipntip001

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