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DNACY CISCO GUIDE FOR FINAL EXAM


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DnaCy 1

What do we will cover in this paper:

Roles of ISP Technicians OSI model & Troubleshooting approaches Protocols Router Configuration


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Roles of ISP Technicians:When a user initially contacts the help desk to resolve an issue, the call or message is usually

directed to a Level 1 support technician. Level 1 support is usually an entry-level position that provides

junior technicians with valuable experience. Many customer issues are resolved by the Level 1 support

technician.

Issues that cannot be resolved are sent to Level 2 support, which typically has fewer agents

available. The duties and responsibilities of the Level 2 technician are similar to that of the Level 1

technician, but they are at a higher skill level. These agents are expected to solve problems that are

more challenging and require more knowledge.

First Level Support Responsibility: Diagnose basic network connectivity issues. Diagnose and document the symptoms of hardware, software and system

problems.

Resolve and document any basic user issues. Help customers complete online order forms to attain various systems,

services, hardware, software, reports and entitlements. Escalate unresolved issues to the next level.

Second Level Support Responsibility: Diagnose and solve more difficult network problems. Use diagnostic tools and remote desktop sharing tools to identify and fix

problems. Identify when an onsite technician must be dispatched to perform repairs.

Third Level Support Responsibilities: Diagnose and resolve problems that have been escalated by the level 1 and

level 2 technicians.

Survey network conditions for analysis by a senior network technician. Install and configure new equipment, including customer premise

equipment upgrades, when necessary.


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OSI MODEL

ApplicationLayer

PresentationLayer

Session Layer Transport Layer Network Layer Data Link Layer Physical Layer

Understanding OSI Model:

Application Layer:

Defines interfaces between application software and networkcommunication functions.

Provides standardized services such as file transfer between systems.Presentation Layer:

Standardizes user data formats for use between different types ofsystems. Encodes and decodes user data. Compresses and decompresses data.

Session Layer:

Manages user sessions and dialogues. Manages links between applications.

Transport Layer:

Manages end to end message delivery over the network. Can provide reliable and sequential packet delivery through error

recovery and flow control mechanisms.

Network Layer:

Provides logical network addressing. Routes packets between networks based on logical addressing.


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Data Link Layer:

Defines procedures for operating the communication links. Detects frame transmit errors and provides a recovery mechanism. Adds physical address to frame.

Physical Layer: Defines physical means of sending data over network devices. Interfaces between network medium and devices. Defines optical, electrical and mechanical characteristics for both

wired and wireless media.

Includes all form of electromagnetic transmission such as light,electricity, infrared and radio waves.


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Troubleshooting MethodologiesThere are three main troubleshooting approaches when using network models:

Top Down Bottom Up Divide and Conquer

Top Down Approach:Starts with the Application Layer and moves down. Itlooks at the problem from the point of view of the user and the application.

Bottom Up Approach:Starts with the Physical Layer and moves up. The

Physical Layer is concerned with hardware and wire connections.


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Divide and Conquer Approach:Typically troubleshooting begins at one of themiddle layers and moves up or down from there.

Troubleshooting by OSI layers:

Physical Layer:

Performance lower than baselineo Inadequate cable or poor termination can result in

errors that increase the rate of retransmissions.

o Electrical interference may cause poor performanceover copper links.

o Cabling that exceeds the recommended standarddistance limitations can cause attenuation problems.

o In a wireless networks, interference or a significantincrease in traffic can cause network responses to

degrade.

Loss of connectivityo

Intermittent loss can be caused by power relatedproblems such as failing UPS or power supply, resulting

in a device reboot or temporary link or device failure.

o Loose connections and tensions on the connectors andwires can also cause intermittent loss.

o For wireless coverage areas, intermittent connectivitycan be caused by overlapping wireless channels.


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o Complete loss can be caused by a cable connectionfailure or a failed device or interface.

High collision countso Average collision counts on shared media should

generally be below 1% of total traffico Collision based problems are often traced to a single

source, such as bad uplink cable on a hub or switch port,

or a link that is exposed to external electrical noise.

o Too many hosts on a single shared segment cancontribute to high collision rates.

o Duplex mismatches between devices can cause collisionsto be recorded on a switch link.

o A full-duplex switch port should have no collisions.

Network Diagrams:It is very difficult to troubleshoot any type of network issue,

without a network diagram that depicts the IP addresses, IP routes and

devices such as firewalls and switches. Logical and Physical topologies

are extremely useful in troubleshooting.

Physical Network Topologies:A Physical network topology shows the physical layout of the

devices connected to the network. Knowing how devices are Physically

connected is necessary for troubleshooting problems at the Physical

Layer, such as cabling or hardware problems. Physical network

topologies typically include:

Device types Models and manufacturers of devices Locations Operating System versions Cable types and identifiers Cabling endpoints


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Logical Network Topologies:A logical network topology shows how data is transferred on the

network. Symbols are used to represent network elements such as

routers, servers, hubs, hosts and security devices. Logical networktopologies typically include:

Device identifiers IP addresses and subnet masks Interface identifiers Routing protocols Static and default routes Data Link protocols WAN technologies


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ProtocolsProtocols are divided into two categories based on their use of connection:

Connection Oriented Protocols:These protocols require that a logical connection

be established between two devices before transferring data. This is generally accomplished by

following a specific set of rules that specify how a connection should be initiated, negotiated,

managed and eventually terminated. Usually one device begins by sending a request to open a

connection, and the other responds. They pass control information to determine if and how the

connection should be set up. If this is successful, data is sent between the devices. When they

are finished, the connection is lost.

Connectionless Protocols:These protocols do not establish a connection betweendevices. As soon as a device has data to send to another, it just sends it.

HTTPS: Hypertext Transfer Protocol w/ Secure Sockets Layer (SSL)Provides encrypted communication and secure identification of a network

web server. HTTPS connections are often used for payment transactions and for

sensitive data transmission.


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Router

Configuration

Changing hostname. Initial

configuration.

Router> enableRouter# configure terminalRouter(config)# hostname megatr0nz@cronusmegatr0nz@cronus(config)#

Specify an encrypted password

to prevent unauthorized access

to the router.

megatr0nz@cronus# configure terminalmegatr0nz@cronus(config)# enable secret @password@megatr0nz@cronus# end

Disable the router from

translating typos into IP

addresses.

megatr0nz@cronus# configure terminalmegatr0nz@cronus(config)# no ip domain-lookup

megatr0nz@cronus# end

Set the IP address and subnet

mask for the specified interface.

megatr0nz@cronus(config)# interface FastEthernet 0/0megatr0nz@cronus(config-if)# ip address 192.168.10.1 255.255.255.0

Set the encapsulation method

for a Serial interface.

megatr0nz@cronus# configure terminalmegatr0nz@cronus(config)# interface Serial 0/0/0megatr0nz@cronus(config-if)# encapsulation hdlc

Encrypt system passwords in

the configuration file.

megatr0nz@cronus# configure terminal

megatr0nz@cronus(config)# service password-encryption

Configure the default route. megatr0nz@cronus# configure terminalmegatr0nz@cronus(config)# ip route 0.0.0.0 0.0.0.0 Serial 0/0/0

Configure DHCP service. megatr0nz@cronus#configure terminal

megatr0nz@cronus(config)# ip dhcp pool DHCP_POOL_N1megatr0nz@cronus(dhcp-config)# network 192.168.10.0 255.255.255.0megatr0nz@cronus(dhcp-config)# dns-server 8.8.8.8megatr0nz@cronus(dhcp-config)# default-router 192.168.10.254megatr0nz@cronus(dhcp-config)# ip dhcp excluded-address 192.168.10.254


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Cisco Router Show Commands

View version information show version

View current configuration (DRAM) show running-config

View startup configuration (NVRAM) show startup-config

Show IOS file and flash space show flash

Shows all logs that the router has in its memory show log

View the interface status of an interface show interface

Overview all interfaces on the router show ip interfaces brief

View type of serial cable on Serial 0/0/0 show controllersSerial 0/0/0

Display a summary of connected cdp devices show cdp neighbor

Display detailed information on all devices show cdp entry *

Display current routing protocols show ip protocols

Display IP routing table show ip route

Display access lists, this includes the number of displayed

matches

show access-lists

Check the router can see the ISDN switch show isdn status

Check a Frame Relay PVC connections show frame-relay pvc

show lmi traffic stats show frame-relay lmi

Display the frame inverse ARP table show frame-relay map

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