ccent notes part-4

8/9/2019 CCENT Notes Part-4

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CCENT Notes

Part 4 Wide-Area Networks

Ref : CCENT/CCNA ICND1 Official Exam Certification Guide, Second Edition

by Wendell Odom

It is highly recommended that you read at least once the above study guide to make full

use of this notes, it is expected that there may be minor errors in this notes, please

always refer the study guide for accurate information.

(Jojo Jacob - CCENT)


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TABLE OF CONTENTS

Chapter 16 WAN Concepts .............................................................................................. 3

Chapter 17 WAN Configuration .....................................................................................15

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Chapter 16 WAN Concepts

WAN Technologies

Voice calls with PCM (Pulse Code Modulation) codec in use consumes 64 Kbps throughthe digital part of the PSTN (when using links like T1 and T3s inside the Telco)

Analog Modems

A Telephone converts sound waves into analog electrical signals, a modem converts a

stream of binary digits on a computer to into representative analog electrical signal.

The modems modulates and de-modulates the analog signals at the sending and receiving

ends.

Modems create an asynchronous circuit, but a leased line creates a synchronous circuit

with CSU/DSUs synchronizing the speeds.

Analog Modems basically uses the dial-up technology and max. speed is around 100

kbps..

Digital Subscriber Line (DSL)

Comparison between DSL and ModemSome of the key features of DSL service

DSL allows analog voice signals, and digital data signals to be sent over the same

local loop wiring at the same time

The local loop must be connected some thing besides the traditional voice switch at

the local CO, in this case a device called DSL Access Multiplexer (DSLAM).

DSL allows for a concurrent voice call to be up at the same time as the dataconnection

Unlike modems, the DSL data component is always on, in other words you dont

have to signal or dial a phone number to set up a data circuit.

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DSL Connection from Home to an ISPTypical topology and devices used for DSL

TELCO - CO

HOME

`

Ethernet

DSL

Router /

Modem

Digital

Signal

> 4000 Hz

DTMF Tones,

Analog Voice,

0 4000 Hz

Local Loop

IP Network

Owned by ISP

PSTN

DSLAM

IP Traffic

Split to ISP

Router

Analog Voice

Split to Voice

Switch

Voice Switch

w/PCM

Telephone wall jack in uses RJ-11 connectors.

RJ11 is aphysical interface often used for terminating telephone wires. It is probably the

most familiar of the registered jacks, being used for single line POTS telephone jacks inmost homes across the world.

RJ14 is similar, but for two lines, and RJ25 is for three lines.RJ61is a similar registered

jack for four lines. The telephone line cord and its plug are more often a true RJ11 with

only two conductors.

Phone generates analog signals at the rate of 0 4000 Hz, and the DSL modem uses

frequencies higher than 4000 Hz, so that the phone and the DSL signals interfere very

much, still need to use a filter.

The DSLAM directs (multiplexes) the analog voice signals frequency range between 0Hz and 4000 Hz, to a voice switch.

4
http://en.wikipedia.org/wiki/Physical_interfacehttp://en.wikipedia.org/wiki/Telephonehttp://en.wikipedia.org/wiki/Registered_jackhttp://en.wikipedia.org/wiki/Plain_old_telephone_servicehttp://en.wikipedia.org/wiki/RJ61http://en.wikipedia.org/wiki/RJ61http://en.wikipedia.org/wiki/RJ61http://en.wikipedia.org/wiki/Physical_interfacehttp://en.wikipedia.org/wiki/Telephonehttp://en.wikipedia.org/wiki/Registered_jackhttp://en.wikipedia.org/wiki/Plain_old_telephone_servicehttp://en.wikipedia.org/wiki/RJ61


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Two views of an RJ25 6P6C crimp-on style connector. .

RJ11 is aphysical interface often used for terminating telephone wires. It is probably themost familiar of the registered jacks, being used for single line POTS telephone jacks in

BS6312 431A plug; colloquially, a British Telecom plug. Used in NZ.

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http://en.wikipedia.org/wiki/Physical_interfacehttp://en.wikipedia.org/wiki/Telephonehttp://en.wikipedia.org/wiki/Registered_jackhttp://en.wikipedia.org/wiki/Plain_old_telephone_servicehttp://en.wikipedia.org/wiki/File:British_Telephone_connector.jpghttp://en.wikipedia.org/wiki/File:Rj11_connector.jpghttp://en.wikipedia.org/wiki/Physical_interfacehttp://en.wikipedia.org/wiki/Telephonehttp://en.wikipedia.org/wiki/Registered_jackhttp://en.wikipedia.org/wiki/Plain_old_telephone_service


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DSL Types

Symetric DSL means that link speed in both directions is the same, and Asymetric meansmore download speed as compared to a relatively low upload speed.

Acronym Spelled Out Type

ADSL Asymetric DSL Asymmetric

CDSL (G.lite) Consumer DSL Asymmetric

VDSL Very-high-data-rate DSL Asymmetric

SDSL Symmetric DSL Symmetric

HDSL High-data-rate DSL Symmetric

IDSL ISDN DSL Symmetric

Factors that affect speed of DSL line.

The speed of a DSL line can vary based on many factors, including The distance between the CO and the consumer (the longer the distance, the slower

the speed)

The quality of the local loop cabling (the worse the wiring, the slower the speed)

The type of DSL (each standard has different maximum theoretical speed)

The DSLAM used in the CO, (older equipment may not have, recent improvements

that allow for faster speeds, on lower grade local loops)

Theoretical maximum speed of an ADSL line on local loop is 10 Mbps (8.192 Mbps).Most ISPs quote it as 1.5 Mbps downstream, 384 kbps upstream.

ADSL support local loops upto 18,000 feets, 5 Kms.

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CABLE Internet

CABLE Company Facitlity

HOME

`

Ethernet

Cable

Modem

HEADEND

ISP Router

TV

F-connectors

Spiter

SATELITE

The equipment at the Head End splits the channels used for internet over to an ISPRouter.

Comparison of Analog, DSL and Cable ModemComparison points for Internet AccessTechnologies

Analog Modem DSL Cable Modem

Transport Telco Local loop Telco Local loop CATV Cable

Supports symmetric Speeds Yes Yes No

Supports asymmetric speed Yes Yes YesTypical practical speed Upto 100kbps 1.5 Mbps

downstream

3 6 Mpbs

downstream

Allows concurrent voice and

data

No Yes Yes

Always-on Internet Service No Yes Yes

Local loop distance issue No Yes No

Throughput degrades under

higher loads

No No Yes

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ATM Packet Switching Service

ATM supports much higher physical link speed compared to Frame relay, especiallywhen using specification called Synchronous Optical Network (SONET).

ATM does not forward frames as in Frame relay, but it forwards Cells. ATM cells arealways fixed 53 bytes in length. 48 bytes of payload (data) and 5 byte header.

ATM header contains two fields that act like Data link connection identifier (DLCI) inframe relay, by identifying each VC (Virtual Channel) , these two fields are called,

Virtual Path Identifier (VPI) and Virtual Channel Identifier (VCI).

When a router need to convert an Ethernet frame into an ATM cell, it creates the ATMcells by splitting the data link frame into 48 bytes segments, each segment is placed in a

cell with 5 byte header. The other end router does the reassembly of ATM cells to

Ethernet frames. The whole process of segmenting frame into cells and reassembling

them is called segmentation and reassembly (SAR).

Circuit Switching : is the physical ability to send or receive data and voice across two end

points.

Packet Switching : The device interpret the bits, and decides forwarding decisions basedon some type of address fields in the header.

Comparison of circuit switching and packet switching.

Features Circuit switching Packet switching

Service implemented as OSI Layer 1 2Point-to-Point (two devices) or more Point-to-Point Multi point (more than two)

IP Services for Internet Access

Besides basic routing, the access router needs to perform three additional important

functions, assigning addresses, learning routes, and translate address. (NAT).

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Internet access equipments separate devices.

`

PC1

Fa0/0

DSLRouter /Modem

R1

`

PC2

ISP1

Fa0/1

Cable Modem

CATV CableISP/Internet

Fast EthernetInterfaces

IP Addressesare in same

subnet

Address assignment on Internet Access Routers.

Factors that impact the IP Addresses used by internet access routers.

The internet access router (R1) has two interfaces, one facing the internet, andother facing the devices at that site, the router needs IP addresses on each of these

interface, the IP addresses are chooses as per the following rules

The internet facing interfaces need one public IP address so that the routers in the

internet knows how to route packet to the access router

The ISP typically assigns that public (globally routable) ip address dynamicallyusing DHCP.

The local PCs typically needs to dynamically learn IP addresses using DHCP, so

the access router acts as a DHCP server for the local hosts.

The router needs a statically configured ip address on the local subnet, using a

private network number

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The local LAN subnet will use ip address in private network number.

DHCP Client and Server Function in an Access Router

`

PC1

192.168.1.1

R1

`

PC2

ISP1

ISP/Internet

192.168.1.101/24

GW 192.168.1.1

DNS 198.133.219.2

192.168.1.102/24

GW 192.168.1.1

DNS 198.133.219.2

R1 as DHCP Server R1 as DHCP Client

DHCP Server

64.100.1.1/30

GW 64.100.1.2

DNS 198.133.219.2

64.100.1.2

ISPs DNS Server

198.133.219.2

Access router is part of the Integrated DLS/Cable Modem. And is a customer locatedequipment.

Access router R1 needs a statically configured IP address on its local LAN facinginterface, a DHCP server function enabled on that interface, and DHCP client function

enabled on its internet facing interface.

Routing for the Interface Access Router

The access router creates a default route with its default gateway(ISP router interface) asits next-hop router.

The default gateway settings on the locals PCs, along with the default route on the accessrouter allows PCs to send packets that reach internet.

However the traffic from internet to local PCs are incomplete, as the internet routes willnever have a route for the private ip address for hosts PC1 and PC2, this problem is

solved by NAT and PAT.

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NAT and PAT

NAT : Network Address Translation

PAT : Port Address Translation

ISP try to conserve public IP address by assigning only minimum (one) public IP address

to each access router, not to each local hosts connected to it.

A key concept of PAT : there is no important difference between some number of TCPconnections from different hosts, versus the same number of TCP connections from the

same hosts.

Three connections from three PCs

PC

PC

PC

64.100.1.1

64.100.1.2

64.100.1.3Server

128.107.1.1

Internet

64.100.1.1 Port 1024

64.100.1.2 Port 1024

64.100.1.3 Port 1033

128.107.1.1 Port 80

128.107.1.1 Port 80

128.107.1.1 Port 80

Three connections from ONE PC

PC

64.100.1.1

Server

128.107.1.1

Internet

64.100.1.1 Port 1024

64.100.1.1 Port 1025

64.100.1.1 Port 1026

128.107.1.1 Port 80

128.107.1.1 Port 80

128.107.1.1 Port 80

The top part of the figure shows a network with three different hosts connecting to a webserver using TCP. The bottom part shows three TCP connection from a single host. All

six connection connect to Server 128.107.1.1 port 80. In each of these cases the server is

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able to differentiate between each connection, because each has a unique combination of

IP address and port number.

PAT allows the local hosts to use private ip addresses, while the access router uses a

single public ip address. PAT takes advantage of the fact that a sever does not care if it

has one connection each to three different hosts, or three connections to a single host ipaddress.

PAT translates the local hosts private IP address to the access routers public ip address,also to tell which ip packet needs to be sent back which local hosts, router keeps track of

both ip address and TCP/UDP port number.

Shows how PAT translates IP Addresses in an Internet Access Router.

PC1

64.100.1.1

SA 192.168.1.101 S.Port : 1024

R1

1

SA 64.100.1.1 S.Port : 1024

2

Server

128.107.1.1

DA 64.100.1.1 D.Port : 1024

DA 192.168.1.101 D.Port : 1024

3

4

NAT Translation Table

Inside Local Inside Global192.168.1.101:1024 64 .100.1.1 : 1024

192.168.1.102:1024 64 .100.1.1 : 1025

The numbered steps in the figure follow the logic.

1. PC1 sends a packet to server 128.107.1.1 and as per PC1s default gateway setting

send the packet to access router R1.

2. R1 performs PAT, based on the on the routers NAT translation table, changing the

local hosts private ip address to routers public ip address, R1 then forwards the packet

based on its default route

3. When the server replies to the packet sent from PC1, server sends the packet to router

R1s address, with a destination port 1024. Internet routers know how to forward thepacket to R1, because it uses a public ip address.

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4. R1 changes the destination ip address and port based on the NAT table, switching

destination ip address/port from 64.100.1.1 : 1024 to 192.168.1.101 : 1024 and R1 knows

the route to reach 192.168.1.101 because this address is in subnet connected to R1.

NAT uses the following key terms

Inside Host : Refers to a host inside the enterprises network

Inside Local : Refers to an IP address in an IP header, with that address representing a

local host as the packet passes over the local enterprise network. In this case

192.168.1.101 and 102 are inside local IP addresses, and packets at step 1, and 4 in the

above figure shows inside local ip addresses.

Inside Global : Refers to an IP address in an IP header, with that address representing a

local host, as the packet passes over the global internet. In this case, 64.100.1.1 is the one

inside global IP address, and the packets in step 2 and 3 in the above figure show insideglobal ip addresses.

Inside Interface : The router interface connected to the same LAN as the inside hosts

Outside Interface: The router interface connected to the internet

Definitions.

ADSL : Asymmetric Digital Subscriber Line, one of many DSL technologies, ADSL is

designed to deliver more bandwidth downstream, than upstream.

Asymmetric : A feature of many internet access technologies including DSL, cable and

modems, in which downstream transmission rate is higher than the upstream transmission

rate.

ATM : Asynchronous Transfer Mode, The international standard for cell relay, in which

multiple service types, such as voice, video and data, are conveyed in fixed length, 53

byte cells. Fixed length cells allow cell processing to occur in hardware, thereby reducingtransit delays.

DSL : Digital Subscriber Line, Public network technology that delivers high bandwidthover conventional telco local loop copper wiring at limited distance. Typically used as an

internet access technology, connecting use to an ISP.

Inside Global : For packets send to and from host that resides in the trusted part of a

network that uses NAT, a term referring to the IP address used in the headers of that

packets, when those packets traverse the global (public) internet.

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Inside Local : For packets sent to and from hosts that reside in the trusted part of a

network that uses NAT, a term referring to the IP addresses used in the headers of those

packets when they traverse enterprises (private) part of the network.

Modem : Modulator demodulator. A device that converts between digital and analog

signals so that a computer can send data to another computer using analog telephonelines.

NAT : Network Address Translation. A mechanism for reducing the need for globallyunique (public) IP addresses. NAT allows an organization with addresses that are not

globally unique to connect to the internet by translating those addresses into public

addresses, in the globally routable address space.

PAT : Port Address Translation. A NAT feature in which one Inside Global IP address

supports over 65,000 concurrent TCP and UDP connections.

PSTN : Public Switched Telephone Network, A general term referring to variety oftelephone networks and services in place worldwide. Some times called POTS, or Plain

Old Telephone Service.

Symmetric : A feature of many internet access technologies in which downstream

transmission rate is same as the upstream transmission rate.

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Chapter 17 WAN Configuration

Configuring Point-to-Point WAN

Configuring HDLC

No layer 1 or Layer 2 commands are required for a routers Ethernet or serial interface,

by default assumes Ethernet and HDCL as the data link layer protocols respectively. Onlycommand that is required is to configure ip address on the interface, and a no shutdown

command if the interface is administratively down.

Optional and required configuration steps for a serial link between two

routers.Configuration steps on a serial link..

Step 1. Configure Interface IP address using ip address interface subcommand

Step 2. The following tasks are required only when the specifically listed conditions are

true.

a. if an encapsulationprotocolinterface subcommand lists a protocol besides HDLC

already exists on the interface, use encapsulation HDLC interface subcommand to

enable HDLC

b. if the interface status is administratively down, enable the interface using the

no shutdown interface sub command

c. if the serial link is a back to back serial link in a lab, configure the clocking rate using

the clock ratespeedinterface sub command, but only on the one router with the DCE

cable attached, (show controllers serialnumber, command)

Step 3. The following steps are optional, and have no impact on whether the link works

and passes IP traffic.

a. configure the link speed using the bandwidthspeed-in-kbps interface subcommand

b. configure the descriptiontextsubcommand on the interface for documentationpurposes

Configure PPP

To migrate from a working HDLC link (default) to a working PPP link, the onlycommand needed is an encapsulation ppp command on each of the two routers serial

interfaces.

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Configuring and Troubleshooting Internet Access Routers

Internet Access Routers : Configuration Steps

Step 1. Establish IP connectivity, plan and configure from CLI, IP address on the localLAN, so that PC on the LAN can ping the routers LAN interface.

Step 2 : Install and access SDM (Cisco Router and Security Device Manager) , installSDM on the router, and access the routers SDM interface using the PC that can ping

routers ip address

Step 3.Configure DHCP and PAT. Use SDM to configure both DHCP client servicesand PAT services on the router

Step 4. Plan for DHCP services, plan the IP address to be assigned by the router to the

hosts on the local LAN, along with the DNS ip address, Domain name, and defaultgateway settings that the router will advertise

Step 5.Configure DHCP Server, Use SDM to configure DHCP server features on the

router

Step 1. Establish IP Connectivity

IP Address details planned and configured on the local LAN for an internet access router.

a. Choose any private IP network number (generally a class c 192.168.1.1 network)

b. choose a mask that allows for enough hosts (typically the default mask is fine)

c. choose the router ip address from the network number

`

PC1

Fa0/0

DSL

Router /

Modem

R1

`

PC2

ISP1

Fa0/1

Cable Modem

CATV CableISP/Internet

Fast Ethernet

Interfaces

IP Addresses

are in samesubnet

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Step 2. Install and Access SDM

Installation and accessing SDM from a host requires ip connectivity between host and the

router, and additional steps and configuration as per the SDM installation manuals.

Step 3 Configuring DHCP and PAT

Pleas refer to page 549 through to 554 for SDM configuration wizards . which asks for

the user inputs and configures the router DHCP client and PAT features.

Step 4. Plan for DHCP services

The following lists outlines the key items that you need to gather before you configure

the router as a DHCP server, the first two items related to planning on the local LAN, andthe last two items are values learned from the ISP, that just needs to be passed on to the

hosts in the local LAN.

1. Recall the private network number and the mask used on the local LAN, and choose a

subset of that network, that can be assigned to hosts using DHCP

2. Make a note of the routers ip address in that network, this address will be the local

hosts default gateway

3. Find the DNS server ip address learned by the router using DHCP client services, use

the show dhcp server exec command, the router will then be able to inform the DNS

sever ip address to the hosts in the local LAN

4. Find the domain name, again with the show dhcp server exec command

Step 4. Configure DHCP server

Pleas refer to page 556 and 557 for SDM DHCP server configuration wizards . which

asks for the user inputs DHCP pool and DHCP setting learned in the previous steps.

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Internet Access Router Verification

Steps to perform basic verification of the installation of the access routers.common

items to check when troubleshooting access router installation

Step 1. Go to a PC on the local LAN and open a web page, if it works fine, then the

access router configurations worked, otherwise go to step 2.

Step 2. Try the ipconfig/all , command prompt command to verify the host has the

correct IP address, dhcp settings, DNS setting as per the configured DHCP server

configurations on the router, otherwise try ipconfig/release and ipconfig/renewcommands to lease a new ip address.

Step 3. Check the cabling and inside interface and outside interface as per the PAT

configurations

Step 4. Test the PAT functionality by generating traffic from a local pc to a host in thenetwork

EXEC commands on the access router for configuration verification

Show ip dhcp binding lists ip addresses assigned on the local lan

Show ip nat translation lists the NAT translation table entries

Clear ip nat translation * - clears the NAT translation table entries

Please refer to page 558 for a output listing of the above commands

Definitions

Cisco Router and Security Device Manager : Administrative web based interface on a

router, that allows for configuration and monitoring of a router, including the

configuration of DHCP, and NAT/PAT.

Please refer to page540 for the Chapter 17 WAN configuration quiz.

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