Open Shortest Path First (OSPF)

Open Shortest Path First (OSPF)

It’s a standard protocol supported by every vendor .
Its ospf v2.
It uses Djikstra’s algorithm to calculate shortest distance.
Its metric is cost. (10^8/bw), its chooses the path where it gets the lowest cost.
It uses unlimited no. of hops.

AD IS 110.
IT’S a classless routing protocol.
It supports vlsm.
It’s a dynamic category’s protocol.
Ospf uses the concept of areas, because it supports larger network

There are so many areas but ther e must be area 0 which is called area 0 in whole OSPF.

TYPES OF ROUTER WHEN USES AREA’S CONCEPT.

i.Internal Router:- when all interface come under singel area.
ii.Backbone router :- when atleast one interface comes under backbone area (arae 0)
iii.Area Border Router (ABR):- when router connect any two areas.
iv.Autonomous System Border Router(ASBR):- router connects any tow different autonomous areas.

OSPF Configuration:-

To configure OSPF we need some following terms:-

i.Process ID:- it’s a unique no. assigned on each router to configure router. Its range is from 1 to 65535.

ii.Wild card mask:- its given on router when we assign network on router.

iii.WCM = broadcast ip - subnet mask.

iv.Example – let we calculate acm of 10.0.0.0

WCM of 10= 255.255.255.255 - 255.0.0.0

WCM = = 0.255.255.255.

ROUTER ID:- it’s a unique identity of each router. The highest ip on a router is called the router id
To change router id-
R(config)#router ospf 1

#router-id 1.2.3.4

#do wr
OSPF timer: -

Hello timer- 10 sec
Dead interval – 40 sec

•R(config)#router ospf 10
• R(config)#network 10.0.0.00 0.255.255.255 area 0
•Where 10 is process id, 10.0.0.0 is network , 0.255.255.255 is wcm and area 0 is router area id.

Virtual Areas:-

R(config)#router ospf 10
 R(config)#area 1 virtual-link 20.0.0.1

Enhanced Interior Gateway Routing Protocol (EIGRP)

Enhanced Interior Gateway Routing Protocol (EIGRP)

EIGRP is a classless protocol, and thus supports VLSMs
EIGRP applies an Administrative Distance of 90 for routes originating within the local Autonomous System

EIGRP uses Bandwidth and Delay of the Line, by default, to calculate its distance metric
EIGRP has a maximum hop-count of 224.
Calculates its best path on bandwidth and delay
Formula (10^7/bandwidth + delay/10) *256
Serial 20000 ms (delay)
FE 1000 ms (delay)
E 10000 ms (delay)

EIGRP Table:-

Builds three separate tables: -
Neighbor table – list of all neighboring routers. Neighbors must belong to the same Autonomous System 

Topology table – list of all routes in the Autonomous System •
Routing table – contains the best route for each known network

EIGRP forms neighbor relationships, called adjacencies, with other routers in the same AS by exchanging Hello packets. Only after an adjacency is formed can routers share routing information.
Default time of hello packet is 5 sec.

Best path is called SUCCESSOR
Value of best path is called FEASIBLE DISTANCE (FD)
Backup path is called FEASIBLE SUCCESSOR (FS)
ADVERTISE DISTANCE- value of neighbour upto destination
Condition for backup path- router choses best path only if AD<FD

EIGRP Packet Types:-

Hello packet- after every 5 sec

UPDATE PACKET – WHENEVER CHANGES OCCUR IN NETWORK


QUERY PACKET – when a router have no best path as well as backup path


REPLY PACKET – IF requested routers have further path to go then they reply back to router as reply packet.

EIGRP router states :-

ACTIVE STATE – when router have no successor and feasible successor
PASSIVE STATE – when router have its both successor and feasible succesor
STUCK IN ACTIVE – when router have no path to go to destination

EIGRP Syntax:-

Like RIP , EIGRP also use directlly connected network
R(config) # router eigrp (10)
R(config) # network 10.0.0.0
R(config) # network 20.0.0.0

Here , 10 is an autonomous number. Eigrp forms neighborship on the basis of A.N.
Autonomous number is locally defined on each router
Without autonomous no. EIGRP couldn’t be configured 

Commands:-

Sh ip route (best path)
Sh ip eigrp topology (chk alternative paths and router state ) 

Sh ip eigrp neighbor (chk neighbors)

IGRP (Interior Gateway Routing Protocol)

IGRP  (Interior Gateway Routing Protocol)

IGRP is an advanced distance vector routing protocol developed by Cisco in the mid-1980s. IGRP has several features that differentiate it from other distance vector routing protocols, such as RIP.

Characteristics of IGRP
Increased scalability - Improved for routing in larger size networks compared to networks that use RIP.

Sophisticated metric - IGRP uses a composite metric that provides significant route selection flexibility. Internetwork delay and bandwidth by default, and optionally reliability, and load are all factored into the routing decision. IGRP can be used to overcome RIP's 15-hop limit. IGRP has a default maximum hop count of 100 hops, configurable to a maximum of 255 hops.

Multiple paths - IGRP can maintain up to six nonequal paths between a network source and destination; the paths do not mandate equal costs like with RIP. Multiple paths can be used to increase available bandwidth or for route redundancy.







Procedure for Configuring IGRP



1.Define IGRP as the IP routing protocol using the router igrp autonomous-system global configuration command.

Router(config)#router igrp 100

2. Assign a major network number to which the router is directly connected using the network network-number router configuration command.

Router(config-router)#network 10.2.2.0

3. Configure load balancing using the variance multiplier router configuration command.

Router(config-router)#variance 1

4. Configure traffic distribution among IGRP load sharing routes using the traffic-share { balanced | min } router configuration command. Router(config- router)#traffic-share balanced

5.Display network information associated with the entire router using the show ip protocol privileged command.

Router#show ip protocols

6. Display the contents of the IP routing table using the show ip route privileged command.

Router#show ip route

RIP (Routing Information Protocol)

RIP (Routing Information Protocol)

RIP, or Routing Information Protocol, is a routing protocol located within IP. There are two versions of RIP supported by Cisco. RIP version 1 and an enhanced version RIPv2, a classless routing protocol.

Characteristics of RIP
•It is a distance vector routing protocol.
•Hop count is used as the metric for path selection.
•The maximum allowable hop count is 15.
•Routing updates are broadcast every 30 seconds by default.
•RIP is capable of load balancing over up to six equal cost paths (4 paths is the default).
•RIPv1 requires that for each major classful network number being advertised, only one network mask is used per network number. The mask is a fixed length subnet mask.
•RIPv2 permits variable-length subnet masks on the internetwork. (RIPv1 does not do triggered updates but RIPv2 does do triggered updates.)

Procedure for Configuring RIP

1.Select RIP as the routing protocol using the router rip global configuration command.

Router(config)#router rip

2. Assign a major network number to which the router is directly connected using the network network-number router configuration command.

Router(config-router)#network 10.2.2.0

3.Display network information associated with the entire router using the show ip protocol privileged command.

Router#show ip protocols

4. Display RIP routing updates as they are sent and received using the debug ip rip privileged command.

Router#debug ip rip

Routing

Routing
Routing is the process by which an item gets from one location to another. Many items get routed: for example, mail, telephone calls, and trains. In networking, a router is the device used to route traffic.

Key Information a Router Needs

Destination Address - What is the destination (or address) of the item that needs to be routed?

Identifying sources of information - From which source (other routers) can the router learn the paths to given destinations?

Discovering routes - What are the initial possible routes, or paths, to the intended destinations?

Selecting routes - What is the best path to the intended destination?

Maintaining routing information - A way of verifying that the known paths to destinations are the most current.

•Routed protocols - Any network protocol that provides enough information in its network layer address to allow a packet to be forwarded from host to host based on the addressing scheme. Routed protocols define the format and use of the fields within a packet. Packets generally are conveyed from end system to end system. The Internet protocol IP is an example of a routed protocol.

Here are some examples of Routed Protocols:
•Internet Protocol (IP)
•AppleTalk (AT)
•Novell NetWare Protocol
•Xerox Network Systems (XNS)

•Routing protocols - Supports a routed protocol by providing mechanisms for sharing routing information. Routing protocol messages move between the routers. A routing protocol allows the routers to communicate with other routers to update and maintain tables. examples of routing protocols are RIP,IGRP,EIGRP and OSPF.

Types of Routing
The different types of routing are:
•Static routing
•Default routing
•Dynamic routing

Static Routing

Routes learned by the router when an administrator manually establishes the route. The administrator must manually update this static route entry whenever an internetwork topology change requires an update.

Benefits:
•There is no overhead on the router CPU.
•There is no bandwidth usage between routers
•It adds security

Disadvantage: •The administrator must really understand the internetwork and how each router is connected to configure routes correctly.
•If a network is added to internetwork, the administrator has to add route to it on all routers-by hand

Default Routing

A default route is a special type of static route. A default route is a route to use for situations when the route from a source to a destination is not known or when it is unfeasible for the routing table to store sufficient information about the route.

In the image, Cisco B is configured to forward all frames for which the destination network is not explicitly listed in its routing table to Cisco A.

Dynamic Routing

Routes dynamically learned by the router after an administrator configures a routing protocol that helps determine routes. Unlike static routes, once the network administrator enables dynamic routing, route knowledge is automatically updated by a routing process whenever new topology information is received from the internetwork.

Router Metrics

Routing metrics are used by routing algorithms to determine the desirability of a given route to a destination network. Different routing protocols implement different routing metrics. Routing metrics represent network characteristics. Metric information is stored in routing tables. There are a number of commonly used routing metrics, including:

•Path length
•Reliability
•Delay
•Bandwidth
•Load
•Cost

Hop count is a value that counts the number of intermediate systems (such as
routers) through which a packet must pass to travel from the source to the
destination. The path length is the sum of all the hops in the path.

The reliability routing metric can be based on any of a number of network characteristics. These include:
•Bit-error rate (the ratio of received bits that contain errors)
•How often each network link fails, and, once down, how quickly each network link can be repaired.

The delay routing metric is based on the length of time required to move a packet from the source to a destination through the internetwork.

Bandwidth
The bandwidth routing metric is based solely on the available traffic capacity of each network link. However, routes through links with greater bandwidth do not necessarily provide better routes than routes through slower links.

Load

The load routing metric is based on the degree to which a network resource (such as a router) is busy. Load is calculated according to such factors as:
•CPU utilization
•Packets processed per second

Cost

The cost routing metric is based on the monetary cost of using each network link. For example, a slower company-owned link can be configured as preferable over faster public links that cost money for usage time.

Routing protocols are used between routers to determine paths and maintain routing tables. Dynamic routing relies on a routing protocol to disseminate knowledge.

Autonomous Systems

An autonomous system is a collection of networks under a common administrative domain

Adminstrative Distance
Multiple routing protocols and static routes may be used at the same time. If there are several sources for routing information, an administrative distance value is used to rate the trustworthiness of each routing information source.

An Administrative Distance is a rating of the trustworthiness of a routing information source, such as an individual router or a group of routers. It is an integer from 0 to 255.

Distance Vector Protocols

Distance vector routing protocols require routers to periodically send all (or a significant portion) of their routing table in routing updates, but only to neighboring routers.

Routing Loop

Routing loops are, simply, the continuous forwarding of packets due to some fault in a network. Packets are continuously looped throughout a particular network or segment.

What Causes Routing Loops?
Routing loops can occur when routing decisions are based on incorrect information, resulting in packets taking paths that return them to already visited routers. They are created due to a variety of circumstances

How Do Routers Prevent Loops?
Routing protocols implement a variety of features designed to prevent routing loops.

•Maximum Hop count
•Split Horizon
•Route Poisoning
•Holddowns

distance vector protocols define infinity as some maximum number. This number refers to a routing metric, such as a hop count.

With this approach, the routing protocol permits the routing loop until the metric exceeds its maximum allowed value. The image shows this defined maximum as 16 hops. Once the metric value exceeds the maximum, network 10.4.0.0 is considered unreachable.

Split Horizon

The rule of split horizon is that it is never useful to send information about a route back in the direction from which the original packet came.

Route Poisoning
With this technique, the router sets a table entry that keeps the network state consistent while other routers gradually converge correctly on the topology change. Used with hold-down timers, which are described soon, route poisoning is a solution to long loops.

Hold-Down
A hold-down timer is a state into which a route is placed so that routers will neither advertise the route nor accept advertisements about the route for a specific length of time (the holddown period). A route is typically placed in holddown when a link in that route fails.

Examining the Register Configuration

Examining the Register Configuration
The configuration register is a 16-bit register. The lowest four bits of the configuration register (bits 3, 2, 1, and 0) form the boot field.

You can change the default configuration register setting with the enabled config-mode config-register command.

Examining the IOS Copy Command
Router#show flash

System flash directory:

File Length Name/status

1 10084696 c2500-js-l_120-3.bin

[10084760 bytes used, 6692456 available, 16777216 total]

16384K bytes of processor board System flash (Read ONLY)

Router#copy tftp flash

Address or name of remote host? 10.1.1.1

Source filename? c2500-js-l_120-3.bin

Accessing tftp://10.1.1.1/c2500-js-l_120-3.bin...

Erase flash befor copying? [Enter]

Erasing the flash filesystem will remove all files! Continue? [Enter]

Erasing device... eeeee(output omitted) ...erased

Erase of flash: complete

Loading c2500-js-l_120-3.bin from 10.1.1.1 (via Ethernet0): !!!!!!!!!!!!!!!!!!!!

(output omitted)

[OK - 10084696/20168704 bytes]

Verifying checksum... OK (0x9AA0)

10084696 bytes copied in 309.108 secs (32636 bytes/sec)

Router#

The following example demonstrates the sequence of commands you would enter to configure various passwords on a router with the following characteristics:

Console password is cisco

Telnet password is cisco

Privileged Mode password is cisco

Secret password is cisco

Router(config)#line console 0

Router(config-line)#login

Router(config-line)#password cisco

Router(config-line)#exit

Router(config)#line vty 0 4

Router(config-line)#login

Router(config-line)#password cisco

Router(config-line)#exit

Router(config)#enable password ccna

Router(config)#enable secret cisco

Router(config)#service password-encryption

interface Command Syntax

router(config)#interface ethernet 1

router(config-if)#ip address 10.1.1.1 255.0.0.0

router(config-if)#no shut

The following example demonstrates the sequence of commands you would enter to configure a serial line on a router with the following characteristics:

•Router interface is serial 0
•Clock Rate is 64000
•Bandwidth is 64 kbits
•Router#configure terminal
•Router(config)# interface serial 0
•Router(config-if)#clock rate 64000
•Router(config-if)#bandwidth 64
•Router(config-if)# exit
•Router(config)# exit
•Router# show interface serial 0
•Serial 0 is up, line protocol is up

•Hardware is HD64570... MTU 1500 bytes, BW 64000 Kbit,...

Overview of Cisco Device Startup

Overview of Cisco Device Startup
1.This event is a series of hardware tests to verify that all components of the router are functional. POST executes from microcode resident in the system ROM.

2.Bootstrap code is used to perform subsequent events like finding the IOS software, loading it, and then running it.

3. The bootstrap code determines where the IOS software to be run is located. The configuration register, configuration file, or Flash memory are the normal places to house the IOS image.

4. Once the bootstrap code has found the proper image, it then loads that image into RAM and starts the IOS running

5. The default is to look in NVRAM for a valid configuration.
6. The desired configuration for the router is loaded and executed.

Setup: The Initial

Configuration Dialog
Router#setup

--- System Configuration Dialog ---

Continue with configuration dialog? [yes/no]: yes

At any point you may enter a question mark '?' for help.

Use ctrl-c to abort configuration dialog at any prompt.

Default settings are in square brackets '[]'.

Basic management setup configures only enough connectivity

for management of the system, extended setup will ask you to configure each interface on the system

Would you like to enter basic management setup? [yes/no]: no

Setup Interface Summary

First, would you like to see the current interface summary? [yes]:

Interface IP-Address OK? Method Status Protocol

BRI0 unassigned YES unset administratively down down

BRI0:1 unassigned YES unset administratively down down

BRI0:2 unassigned YES unset administratively down down

E0 unassigned YES unset administratively down down

Serial0 unassigned YES unset administratively down down

Setup Initial

Global Parameters

Configuring global parameters:

Enter host name [Router]:wg_ro_c

The enable secret is a password used to protect access to

privileged EXEC and configuration modes. This password, after

entered, becomes encrypted in the configuration.

Enter enable secret: cisco

The enable password is used when you do not specify an

enable secret password, with some older software versions, and

some boot images.

Enter enable password: rohit

The virtual terminal password is used to protect access to the router over a network interface.

Enter virtual terminal password: thakur

Configure SNMP Network Management? [no]:

Setup Initial

Protocol Configurations
Configure LAT? [yes]: no

Configure AppleTalk? [no]:

Configure DECnet? [no]:

Configure IP? [yes]:

Configure IGRP routing? [yes]: no

Configure RIP routing? [no]:

Configure CLNS? [no]:

Configure IPX? [no]:

Configure Vines? [no]:

Configure XNS? [no]:
Configure Apollo? [no]:

Setup Interface

Parameters
BRI interface needs isdn switch-type to be configured

Valid switch types are :
[0] none..........Only if you don't want to configure BRI.

[1] basic-1tr6....1TR6 switch type for Germany

[2] basic-5ess....AT&T 5ESS switch type for the US/Canada

[3] basic-dms100..Northern DMS-100 switch type for US/Canada

[4] basic-net3....NET3 switch type for UK and Europe

[5] basic-ni......National ISDN switch type

[6] basic-ts013...TS013 switch type for Australia

[7] ntt...........NTT switch type for Japan

[8] vn3...........VN3 and VN4 switch types for France

Choose ISDN BRI Switch Type [2]:

Configuring interface parameters:

Do you want to configure BRI0 (BRI d-channel) interface? [no]:

Do you want to configure Ethernet0 interface? [no]: yes

Configure IP on this interface? [no]: yes

IP address for this interface: 10.1.1.33

Subnet mask for this interface [255.0.0.0] : 255.255.255.0

Class A network is 10.0.0.0, 24 subnet bits; mask is /24

Do you want to configure Serial0 interface? [no]:

Logging In to the Router
Router User-Mode

Command List
Router>?

Exec commands:

access-enable Create a temporary Access-List entry
atmsig Execute Atm Signalling Commands
cd Change current device
clear Reset functions
connect Open a terminal connection
dir List files on given device
disable Turn off privileged commands
disconnect Disconnect an existing network connection
enable Turn on privileged commands
exit Exit from the EXEC
help Description of the interactive help system
lat Open a lat connection
lock Lock the terminal
login Log in as a particular user
logout Exit from the EXEC
-- More --

Router Privileged-Mode

Command List
Router#?

Exec commands:

access-enable Create a temporary Access-List entry

access-profile Apply user-profile to interface

access-template Create a temporary Access-List entry

bfe For manual emergency modes setting

cd Change current directory

clear Reset functions

clock Manage the system clock

configure Enter configuration mode

connect Open a terminal connection

copy Copy from one file to another

debug Debugging functions (see also 'undebug')

delete Delete a file

dir List files on a filesystem

disable Turn off privileged commands

disconnect Disconnect an existing network connection

enable Turn on privileged commands

erase Erase a filesystem

exit Exit from the EXEC

help Description of the interactive help system
-- More --


Enhanced Editing Commands

Major Components of a Router

Major Components of a Router

•Random access memory (RAM) contains the software and data structures that allow the router to function. The principle software running in RAM is the Cisco IOS image and the running configuration.

•Read-only memory contains microcode for basic functions to start and maintain the router.

•Flash is primarily used to contain the IOS software image. Some routers run the IOS image directly from Flash and do not need to transfer it to RAM.

•Non-volatile random access memory is mainly used to store the configuration. NVRAM uses a battery to maintain the data when power is removed from the router.

•Configuration Register The configuration register is used to control how the router boots up.

OSI Network Model

OSI Network Model

There are 7 layers in the OSI model. Each layer is responsible for a particular aspect of data communication. For example, one layer may be responsible for establishing connections between devices, while another layer may be responsible for error checking during transfer.

The layers of the OSI model are divided into two groups: the upper layer and lower layer. The upper layers focus on user applications and how files are represented on the computers prior to transport. For the most part, network engineers are more concerned with the lower layers. It's the lower layers that concentrate on how the communication across a network actually occurs.

ALL People Seem to Need Data Processing (Layer 7 to 1)

Please Do Not Take Sausage Pizzas Away (Layer 1 to 7)

The Application Layer

The Application Layer is the highest layer in the protocol stack and the layer responsible for introducing data into the OSI stack. In it resides the protocols for user applications that incorporate the components of network applications.

Classification of Applications

Computer applications

Network applications

Internetwork applications

Examples: Telnet, FTP, HTTP, WWW Browsers, NFS, SMTP, POP, TFTP .

Presentation LayerThe Presentation Layer manipulates the representation of data for transfer to applications on different devices.

The Presentation Layer is responsible for the following services:
•Data representation
•Data security
•Data compression

Data Representation

Session Layer

The Session Layer establishes, manages, and terminates sessions (different from connections) between applications as they interact on different hosts on a network.

Its main job is to coordinate the service requests and responses between different hosts for applications.

Examples: NFS, SQL, RPC, ASP

Three different communication modes exists for data transfer within a session connection:

•Single-duplex

•Half-duplex

•Full-duplex.

Transport Layer

The basic roles of the Transport Layer are to establish end-to-end connections from one computer to another on the network and provide reliable "transport" of data between devices.

Basic Transport Layer Services:

Resource Utilization (multiplexing)
Connection Management (establishing)
Flow Control (Buffering / Windowing)
Reliable Transport (positive acknowledgment / error checking)

Flow Control Once the connection has occurred and transfer is in progress, congestion of the data flow can occur at a destination for a variety of reasons. Possible options include:

The destination can become overwhelmed if multiple devices are trying to send it data at the same time.

It may become overwhelmed if the source is sending faster than it can physically receive.

Congestion Prevention
The Transport Layer is responsible for providing flow control to alleviate the issue of congestion and provide reliability in the data transfer. Two main methods for flow control include

•Buffering

•Windowing

Buffering

Buffering is a form of data flow control regulated by the Transport Layer. It is responsible for ensuring that sufficient buffers are available in the destination for the processing of data and that is data transmitted at a rate that does not exceed what the buffer can handle.

Windowing

Windowing is a flow control scheme in which the source computer will monitor and make adjustments to the amount of information sent based on successful, reliable receipt of data segments by the destination computer. The size of the data transmission, called the "window size", is negotiated at the time of connection establishment. It is determined by the amount of memory or buffer that is available.

Given a window size of 3, the source (in this case a router) sends 3 data segments to the destination. The destination sends an acknowledgement asking for the next set of data segments.

If the destination does not receive all three of the negotiated data segments, for example, due to a buffer overflow, it sends no acknowledgment. Since the source does not receive an acknowledgment, it knows the data segments should be retransmitted

Network Layer
The Network Layer is the 3rd layer in the OSI model and is responsible for identifying computers on a network. This layer works closely with layer 2 to translate data packets from a logical address (similar to an IP address) into hardware based MAC addresses.

This layer is concerned with 2 functions:
•Routing
•Fragmentation / Reassembly

Two types of packets are used at the Network layer:

Data packets: Used to transport user data through the internetwork. Protocols used to support data traffic are called routed protocols. Eg. IP and IPX.

Route update packets: Used to update neighboring routers about the network connected to all routers within the internetwork. Protocols that send route updates are called routing protocols. Eg. RIP, EIGRP, OSPF

Data Link / Physical Layer
LAN and WAN protocols occupy the bottom two layers of the OSI model. These two layers, Physical Layer and Data Link Layer, work very closely together to ensure data transfer across the physical network. Examples: HDLC, Frame Relay, PPP, ATM, FDDI, IEEE 802.3/802.2

To accomplish accurate delivery, the Data Link Layer provides the following services:

1. Machine address determination of both sending and receiving machines

2. Formatting of Network Layer "packets" into frames with machine addresses attached

3. Sequencing and resequencing of frames transmitted out of sequence

Data Link SublayersLogical Link Control (LLC) responsible for identifying Network layer protocols and encapsulating them.

Media Access Control (MAC) defines how packets are placed on media

Physical Layer The Physical Layer is the lowest layer in the OSI model and is concerned with how the physical structure of the network enables transmission of data. It is responsible for defining the mechanical and electrical specifications for the transmission medium within a connection, as well as the transformation or encoding of data into “bits”.

Examples:EIA/TIA-232, V.35, EIA/TIA-449, RJ-45, Ethernet, 802.3

Protocols defined at the Physical Layer standardize physical connections. Specifications include voltage levels, maximum transmission distances, data rates, and physical connectors.

Each layer depends on the service function of the ISO/OSI layer below it. To provide this service, the lower layer uses encapsulation to put the PDU from the upper layer into its data field; then it can add whatever headers and trailers the layer will use to perform its function.

As networks perform services for users, the flow and packaging of the information changes. In this example of internetworking, five conversion steps occur:

What do the 7 layers really do?
TCP/IP
The Transmission Control Protocol/Internet Protocol (TCP/IP) suite of protocols was developed as part of the research done by the Defense Advanced Research Projects Agency (DARPA).

TCP/IP Protocol Layers•Process/Application Layer
•Transport Layer or Host-to-Host Layer
•Internet Layer
•Network Access Layer

Application protocols exist for file transfer, e-mail, and remote login. Network management is also supported at the application layer.

Transport services allow users to segment and reassemble several upper-layer applications onto the same transport-layer data stream.

TCP Segment
UDP Segment
IP provides connectionless, best-effort delivery routing of datagrams. It is not concerned with the content of the datagrams. Instead, it looks for a way to move the datagrams to their destination.

IP Datagram
Version - Version number (4 bits)

Header Length - Header length in 32-bit words (4 bits)

Priority and Type of Service - How the datagram should be handled. The first 3 bits are priority bits (8 bits).

IP Options - Network testing, debugging, security, and others (0 or 32 bits if any)

ICMP
The Internet Control Message Protocol (ICMP) is implemented by all TCP/IP hosts. ICMP messages are carried in IP datagrams and are used to send error and control messages.

ICMP uses the following types of defined messages:

1. Destination Unreachable

2. Time Exceeded

3. Parameter Problem

4. Subnet Mask Request

5. Redirect

6. Echo

7. Echo Reply

8. Information Request

9. Information Reply

10.Address Request

11.Address Reply

Address Resolution Protocol
Address Resolution Protocol (ARP) is used to resolve or map a known IP address to a MAC sublayer address to allow communication on a multi-access medium such as Ethernet.

The term local ARP is used to describe resolving an address when both the requesting host and the destination host share the same media or wire.

Reverse ARP

Reverse Address Resolution Protocol (RARP) relies on the presence of a RARP server with a table entry or other means to respond to these requests.

ARP and RARP are implemented directly on top of the data link layer

IP Address
In a TCP/IP environment, end stations communicate seamlessly with servers or other end stations. This communication occurs because each node using the TCP/IP protocol suite has a unique 32-bit logical IP address.

Each IP datagram includes the source IP address and destination IP address that identifies the source and destination network and host.

When IP was first developed, there were no classes of addresses. Now, for ease of administration, the IP addresses are broken up into classes.

The bits in the first octet identify the address class. The router uses the first bits to identify how many bits it must match to interpret the network portion of the address

Class A addresses include the following:
•The first bit is 0.
•Range of network numbers: 1.0.0.0 to 126.0.0.0
•Number of possible networks: 127 (1- 126 usable, 127 is reserved)
•Number of possible values in the host portion: 16,777,216.

Class B addresses include the following:
•The first two bits are 10.
•Range of network numbers: 128.0.0.0 to 191.255.0.0
•Number of possible networks: 16,384
•Number of possible values in the host portion: 65,536

Class C addresses include the following:
•The first three bits are 110.
•Range of network numbers: 192.0.0.0 to 223.255.255.0
•Number of possible networks: 2,097,152
•Number of possible values in the host portion: 256

Class D addresses include the following:
•Range of network numbers:
224.0.0.0 to 239.255.255.255

Ethernet

Ethernet
Ethernet was developed by Xerox in 1970. It was implemented through thicknet cable running at 10 Mbps.Ethernet is a connection media access method that allows all hosts on a network to share the same bandwidth of a link.

Ethernet actually just refers to the LAN implementations that includes three principal categories.
•Ethernet / IEEE 802.3---operates at 10 Mbps on coaxial cable and twisted pair cable.
•100-Mbps Ethernet---(also known as Fast Ethernet) operates at 100 Mbps over twisted-pair cable.
•1000-Mbps Ethernet---( also known as Gigabit Ethernet) operates at 1000 Mbps (1 Gbps) over fiber and twisted-pair cables.

Ethernet and IEEE 802.3 operation involves three basic components:
•Transmission
•Media access
•Collision handling

Media Access

The Ethernet media access uses the following process:
•Any station on a LAN can access the network at any time.
•Before sending data, stations listen for traffic on the network.
•A station waits until it detects no traffic before it transmits data.

Collision handling

Ethernet is a "first come, first serve" environment. In such an environment, any station on the network can transmit whenever the network is quiet. A collision occurs when two stations listen for traffic, hear none, and then transmit data at the same time. Both transmissions are damaged, and the stations must retransmit at a later time.


CSMA / CD

Ehernet Cabling

Striaght Through cable: used to connect
•Host to switch or hub
•Router to switch or hub

Four wires are used in straight-through cable to connect Ethernet devices.

1 1

2 2

3 3

6 6

Striaght Through cable: used to connect
•switch to switch
•Router direct to host
•hub to hub
•Host to host

Four wires are used as in straight-through cable to connect Ethernet devices.

1 1

2 2

3 3

6 6

Rolled cable
Although rolled cable is not used to connect any Ethernet connections together, we use this cable to connect a host to a router console serial communication (com) port.

Eight wires are used in this cable to connect serial devices.
•

1 1

2 2

3 3

4 4

5 5

6 6

7 7

8 8

Start HyperTerminal to create a console connection and configure the device.Start Programs accessories communications HyperTerminalProvide the default settings for com1 port

Network Model Overview
In order for a computer to send information to another computer, and for that computer to receive and understand the information, there has to exist a set of rules or standards for this communication process. These standards ensure that varying devices and products can communicate with each other over any network. This set of standards is called a model.

Network Model Advantages

This division provides advantages for the network design, architecture and implementation. These include:

•Reduces complexity - by dividing the processes into groups, or layers, implementation of network architecture is less complex
•Provides compatibility - standardized interfaces allow for "plug-and-play" compatibility and multi-vendor integration
•Facilitates modularization - developers "swap" out new technologies at each layer keeping the integrity of the network architecture
•Accelerates evolution of technology - developers focus on technology at one layer while preventing the changes from affecting another layer
•Simplifies learning - processes broken up into groups divides the complexities into smaller, manageable chunks

Local Area Network Cabling

Local Area Network Cabling

The earliest LANs used coaxial cables. Over time, the twisted pair cables used in telephone systems were improved to carry higher frequencies and support LAN traffic. More recently, fiber optic cables have emerged as a high-speed cabling option.

Local Area Networks use four types of cables:

•Coaxial
•Unshielded Twisted Pair (UTP)
•Shielded Twisted Pair (STP)
•Fiber Optic

Coaxial Cables


A coaxial cable consists of:
•a single copper conductor
•a layer of shielding with a ground wire
•an outer jacket

Coaxial cables are sometimes used for bus topologies, but many LAN products are dropping support of coaxial cable connectivity.

The Ethernet LAN protocol was originally developed to operate over coaxial cables. 10Base5 / Thicknet cable:
•was the original Ethernet cable.
•is no longer in use in modern LANs. 10Base2 / Thinnet cable:
has a smaller diameter than Thicknet.
•replaced Thicknet.
•is no longer recommended, but is still used in some very small LANs.

Unshielded Twisted Pair

Unshielded twisted pair (UTP) cable is used for both LANs and telephone systems. UTP cables are composed of four color-coded pairs of copper conductors twisted around each other. An outer jacket provides protection and keeps the pairs in alignment. UTP cable connects to devices via 8 pin modular connectors called RJ-45 plugs. All LAN protocols can operate over UTP. Most modern LAN devices are equipped with RJ-45 jacks.

Shielded Twisted Pair




STP cable is also used for Data Networks. It originated with IBM's Token-Ring networks. Its shielding allows greater tolerances for protection from EMI interference, such as from flourescent light fixtures and electric motors.

Fiber Optic Cable

Fiber Optic cables are the latest development in cabling technology. They are constructed from optical glass. There is a central glass filament, called the core, and surrounding layers of cladding, buffer coatings, strengthening materials, and an outer jacket.




Information is transmitted by wavelengths of light. This is accomplished through devices that convert electrical signals into rapid pulses of either LED or Laser light.




Fiber optic cables offer several advantages, including:
•high bandwidth capacity (many gigabits per second).
•longer distances between devices (from 2 to over 60 kilometers).
•immunity to electromagnetic interferences

Fiber optic cables are widely used in WANs for both voice and data communications. The primary barrier to their widespread use in LANs is the cost of electronics.

Wide Area Network (WAN) Infrastructure

Wide Area Network (WAN) Infrastructure

As with LANs, there are numerous devices associated with data information flow across a WAN. Together, these devices create the infrastructure of a functional WAN. These devices include:
•Router
•ATM Switch
•Modem and CSU/DSU
•Communication Server
•Multiplexer
•X.25/Frame Relay Switches

ATM Switches

ATM Switches provide high-speed transfer between both LANs and WANs.

Modem (modulator / demodulator)
Modems convert digital and analog signals. At the source, modems convert digital signals to a form suitable for transmission over analog communication facilities (public telephone lines). At the destination, modems convert the signal back to a digital format.

CSU/DSU (Channel Service Unit / Data Service Unit)
CSUs/DSUs are similar to modems, however they send data in digital format across digital telephone loops. They are usually in a physical box, but they may come in two separate units: CSUs or DSUs.


Multiplexers

A Multiplexer combines multiple signals for transmission over a single circuit. This allows for the transfer of various data simultaneously, such as video, sound, text, etc.

Communication Servers

Communication Servers are typically dial in/out servers that allow users to dial in from remote locations and attach to the LAN.

X.25 / Frame Relay Switches
X.25 and Frame Relay Switches connect private data over public data circuits using digital signal. These units are very similar to ATM switches, but the transfer rate of data is not comparable.

Routers

A router is a device that analyzes the contents of data packets transmitted within a network or to another network. Routers determine whether the source and destination are on the same network or whether data must be transferred from one network type to another, which requires encapsulating the data packet with routing protocol header information for the new network type.

Based on designs developed in the 1960s, the Advanced Research Projects Agency Network (ARPANET) was created in 1969 by the U.S. Department of Defense. This early network design was based on circuit switching. The first device to function as a router was the Interface Message Processors that made up ARPANET to form the first data packet network. 

The initial idea for a router, which was then called a gateway, came from a group of computer networking researchers who formed an organization called the International Network Working Group, which became a subcommittee of the International Federation for Information Processing in 1972. 

In 1974, the first true router was developed and by 1976, three PDP-11-based routers were used to form a prototype experimental version of the Internet. From the mid-1970s to the 1980s, mini-computers were used as routers. Today, high-speed modern routers are actually very specialized computers with extra hardware for rapid data packet forwarding and specialized security functions such as encryption. 

When several routers are used in a collection of interconnected networks, they exchange and analyze information, and then build a table of the preferred routes and the rules for determining routes and destinations for that data. As a network interface, routers convert computer signals from one standard protocol to another that's more appropriate for the destination network. 

Large routers determine interconnectivity within an enterprise, between enterprises and the Internet, and between different internet service providers (ISPs); small routers determine interconnectivity for office or home networks. ISPs and major enterprises exchange routing information using border gateway protocol (BGP).




Simple Words:-

Routers are a step up from bridges. They are able to route and filter information to different networks. Some routers can automatically detect problems and redirect information around the problem area. These are called "intelligent routers."

Switches

A switch, in the context of networking is a high-speed device that receives incoming data packets and redirects them to their destination on a local area network (LAN). A LAN switch operates at the data link layer (Layer 2) or the network layer of the OSI Model and, as such it can support all types of packet protocols.

Essentially, switches are the traffic cops of a simple local area network.

A switch in an Ethernet-based LAN reads incoming TCP/IP data packets/frames containing destination information as they pass into one or more input ports. The destination information in the packets is used to determine which output ports will be used to send the data on to its intended destination.

Switches are similar to hubs, only smarter. A hub simply connects all the nodes on the network -- communication is essentially in a haphazard manner with any device trying to communicate at any time, resulting in many collisions. A switch, on the other hand, creates an electronic tunnel between source and destination ports for a split second that no other traffic can enter. This results in communication without collisions.

Switches are similar to routers as well, but a router has the additional ability to forward packets between different networks, whereas a switch is limited to node-to-node communication on the same network.

This definition was written in the context of Networking

Simple Words:- Switches connect all computer LAN connections, the same as hubs do. The difference is that switches can run in full-duplex mode and are able to direct and filter information to and from specific destinations

Hubs

A hub, also called a network hub, is a common connection point for devices in a network. Hubs are devices commonly used to connect segments of a LAN. The hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.

What Hubs Do

Hubs and switches serve as a central connection for all of your network equipment and handles a data type known as frames. Frames carry your data. When a frame is received, it is amplified and then transmitted on to the port of the destination PC. 

Image: Hub and wireless hub network icons

In a hub, a frame is passed along or "broadcast" to every one of its ports. It doesn't matter that the frame is only destined for one port. The hub has no way of distinguishing which port a frame should be sent to. Passing it along to every port ensures that it will reach its intended destination. This places a lot of traffic on the network and can lead to poor network response times.

Compared to a standard switch, the hub is slower as it can send or receive information just not at the same time, but typically costs more than a hub.

Passive, Intelligent and Switching Hubs

A passive hub serves simply as a conduit for the data, enabling it to go from one device (or segment) to another. So-called intelligent hubs include additional features that enables an administrator to monitor the traffic passing through the hub and to configure each port in the hub. Intelligent hubs are also called manageable hubs.

A third type of hub, called a switching hub, actually reads the destination address of each packet and then forwards the packet to the correct port.

Home and Small Business Hubs

Hubs can be used as a standalone device or connected to compatible hubs and switches to form a larger network. Hubs are generally easy to install and maintain, making these devices a good option for home networking. A hub is also easily configured for small business branch office networking.

Bridges

A bridge is a type of computer network device that provides interconnection with other bridge networks that use the same protocol.

Bridge devices work at the data link layer of the Open System Interconnect (OSI) model, connecting two different networks together and providing communication between them. Bridges are similar to repeaters and hubs in that they broadcast data to every node. However, bridges maintain the media access control (MAC) address table as soon as they discover new segments, so subsequent transmissions are sent to only to the desired recipient.

Bridges are also known as Layer 2 switches.

A network bridge device is primarily used in local area networks because they can potentially flood and clog a large network thanks to their ability to broadcast data to all the nodes if they don’t know the destination node's MAC address.

A bridge uses a database to ascertain where to pass, transmit or discard the data frame.

1. If the frame received by the bridge is meant for a segment that resides on the same host network, it will pass the frame to that node and the receiving bridge will then discard it.
2. If the bridge receives a frame whose node MAC address is of the connected network, it will forward the frame toward it.

Simple Words:- Bridges are intelligent repeaters. They regenerate transmitted signals, but unlike repeaters, they can also determine destinations.

Repeaters

1) In digital communication systems, a repeater is a device that receives a digital signalon an electromagnetic or optical transmission medium and regenerates the signal along the next leg of the medium. In electromagnetic media, repeaters overcome theattenuation caused by free-space electromagnetic-field divergence or cable loss. A series of repeaters make possible the extension of a signal over a distance.

Repeaters remove the unwanted noise in an incoming signal. Unlike an analog signal, the original digital signal, even if weak or distorted, can be clearly perceived and restored. With analog transmission, signals are restrengthened with amplifiers which unfortunately also amplify noise as well as information.

Because digital signals depend on the presence or absence of voltage, they tend to dissipate more quickly than analog signals and need more frequent repeating. Whereas analog signal amplifiers are spaced at 18,000 meter intervals, digital signal repeaters are typically placed at 2,000 to 6,000 meter intervals.

2) In a wireless communications system, a repeater consists of a radio receiver, an amplifier, a transmitter, an isolator, and two antennas. The transmitter produces a signal on a frequency that differs from the received signal. This so-called frequency offset is necessary to prevent the strong transmitted signal from disabling the receiver. The isolator provides additional protection in this respect. A repeater, when strategically located on top of a high building or a mountain, can greatly enhance the performance of a wireless network by allowing communications over distances much greater than would be possible without it.

3) In satellite wireless, a repeater (more frequently called a transponder) receives uplink signals and re-transmits them, often on different frequencies, to destination locations.

4) In a cellular telephone system, a repeater is one of a group of transceivers in a geographic area that collectively serve a system user.

5) In a fiber optic network, a repeater consists of a photocell, an amplifier, and a light-emitting diode (LED) or infrared-emitting diode (IRED) for each light or IR signal that requires amplification. Fiber optic repeaters operate at power levels much lower than wireless repeaters, and are also much simpler and cheaper. However, their design requires careful attention to ensure that internal circuit noise is minimized.

6) Repeaters are commonly used by commercial and amateur radio operators to extend signals in the radio frequency range from one receiver to another. These consist of drop repeaters, similar to the cells in cellular radio, and hub repeaters, which receive and retransmit signals from and to a number of directions.



7) A bus repeater links one computer bus to a bus in another computer chassis, essentially chaining one computer to another.

Simple Words:- Repeaters, located within the physical layer of a network, regenerate and propagate signals from one to another. They do not change any information being transmitted, and they cannot filter any information. Repeaters help to extend the distances of networks by boosting weak signals

LAN Infrastructure Devices

There are numerous devices associated with data information flow across a LAN. When adjoined, they create the infrastructure of a functional LAN. These devices include:

•Repeaters
•Bridges
•Hubs
•Switches
•Routers

LAN Transmission Methods

LAN transmission methods fall into 3 main categories:

•Unicast transmission
•Multicast transmission
•Broadcast transmission

Unicast Transmission
In unicast transmissions, a single data packet is sent from a source to a single destination on the network.

Unicast Process
•The source addresses
the packet with the
destination address.

  •The packet is sent into
the network.

•The network delivers the
packet to the destination.


Multicast Transmission

In multicast transmissions, a single data packet is copied and sent to specific destinations on the network

Multicast Process
•The source addresses the packet
using a multicast address.
•The packet is sent into the
network.
•The network copies the packet.
•A copy is delivered to each
destination that is included in the
multicast address.


Broadcast Tranmission
In multicast transmissions, a single data packet is copied and sent to specific destinations on the network

Broadcast Process
•The source addresses the packet with the broadcast address.
•The packet is sent into the network.
•The network copies the packet.
•The packet copies are delivered to all destinations on the
network.

Common LAN Topologies

In computer networking, topology refers to the layout of connected devices. This article introduces the standard topologies of networking.

Topology in Network Design

Think of a topology as a network's virtual shape or structure. This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home network may be arranged in a circle in a family room, but it would be highly unlikely to find a ring topology there.

Network topologies are categorized into the following basic types:

• bus
• ring
• star
• tree
• mesh

More complex networks can be built as hybrids of two or more of the above basic topologies.

Bus Topology

Bus networks (not to be confused with the system bus of a computer) use a commonbackbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.

Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices.

If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.

Illustration: Bus Topology Diagram

Ring Topology

In a ring network, every device has exactly two neighbors for communication purposes.

All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.

To implement a ring network, one typically uses FDDI, SONET, or Token Ringtechnology. Ring topologies are found in some office buildings or school campuses.

Illustration: Ring Topology Diagram

Star Topology

Many home networks use the star topology. A star network features a central connection point called a "hub node" that may be a network hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.

Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)

Illustration: Star Topology Diagram

Tree Topology

A tree topology joins multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the root of a tree of devices. This bus/star hybrid approach supports future expansion of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

Illustration: Tree Topology Diagram

Mesh Topology

Mesh topology introduces the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.

A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.

Illustration: Mesh Topology Diagram

Summary

Topology remains an important part of network design theory. You can probably build a home or small business computer network without understanding the difference between a bus design and a star design, but becoming familiar with the standard topologies gives you a better understanding of important networking concepts like hubs, broadcasts, and routes.