Networking Test Friday Online

My test is online today. All the powerpoint slides posted is basically an overview of what is going to be on the test. Basically the test will have mostly subnetting, the configuration modes and commands, and know the 7 layers in and out very well. I need an A on this test…..I will also accept a B if it comes to that. The information in the powerpoints I post, many Networking experts and people who have there CCNA’s will know this information easily. Please if there is someone who is an expert in networking can get me an A!!!

I am going to post alot of powepoints not everything is going to be on this exam. anyone who has an overall knowledge of all this areas should do well.

ITE PC v4.0

Chapter 1 1

Chapter 1
Introduction to

Routing

and Packet Forwarding

Routing Protocols and Concepts –
Dr. C. BouSaba

ITE PC v4.0

Router Functions

 Connect networks together

 Direct packets to their proper
destination efficiently

 Find best routes

 Switch packets from one
network to another

 Provide

– Security (Permitting or denying
specified types of packet)

– Quality of service (Prioritizing
packets)

ITE PC v4.0

Chapter 1

Router as a computer

 CPU: control unit handles instructions,
ALU for calculations

 RAM: volatile working storage

 ROM: permanent storage for POST
and start-up instructions

 Operating System: software that runs
the computer

 System bus, Power supply
 Long term storage is Flash and

NVRAM, not hard disk

 Range of different interfaces all on
different

networks

 No input/output peripherals.
Connect via a console PC and use
PC’s keyboard and screen

Router VS computer

ITE PC v4.0

Hardware Components of a Router

ITE PC v4.0

Integrated Services Routers

ITE PC v4.0

RAM
 Dynamic random access memory

 Temporary memory while router is on

 Loses content when the router loses
power or is restarted

 Holds running configuration

 Holds routing tables

 Holds ARP cache

 Holds fast-switching cache etc.

NVRAM
 Non-volatile RAM: keeps its contents

when the router is off

 Stores the startup configuration file

 When you have configured a router,
you must save your configuration to
NVRAM if you want to keep it

Flash
 Electronically erasable, programmable

ROM (EEPROM)

 Keeps its contents when the router is off

 Holds the operating system image (IOS)

 Allows the IOS to be updated

 Can store multiple versions of IOS
software if it has enough capacity

 Can be upgraded by adding SIMMs

ROM
 Permanent memory: cannot be upgraded

without replacing the chip

 Holds power-on self test (POST) inst.

 Stores bootstrap program

 Stores ROM monitor SW (for emergency
download of IOS, for password recovery)

 May store basic IOS for emergency use
(less common than it was)

ITE PC v4.0

Router storage

 ROM

 Permanent

 Holds POST, boot instructions,
basic IOS

 Flash

 Keeps contents

 Holds IOS image

 NVRAM

 Keeps contents

 Holds startup configuration
file

 RAM

 Volatile

 Holds running config,
tables, queues etc

ITE PC v4.0

Interfaces

 Can be attached directly to the motherboard (like our Fast
Ethernet or Ethernet interfaces)

 Can be on removable and interchangeable modules (like our
serial interfaces)

 Modules for different serial connections

ITE PC v4.0

Operating system

 As specialized computers, routers and switches need
operating systems.

 Cisco devices use the Cisco Internetwork Operating
System (IOS)

 There are versions for different models of router and
switch, and different feature sets

 The IOS can be upgraded periodically

ITE PC v4.0

Naming IOS image files

 Platform-features-format-version

 c2600-i-mz.122-8.T5

 c2600 is the platform: Cisco 2600 series router

 i is a code for the set of features in this IOS, another is
ipbase

 mz is a code to say that the IOS runs in RAM and the file is
zip compressed

 122-8.T5 is the upgrade version

ITE PC v4.0

IOS storage

 The IOS is stored in the router’s flash memory, often in
compressed form

 Most routers copy the IOS to RAM when they start up

 You need enough space in flash and in RAM if you
upgrade the IOS

 Some of our routers have more features than others – it
depends on the IOS.

ITE PC v4.0

IOS modes

 ROM monitor:

Used to recover from system failure or loss of password

Needs direct access from console port

 Boot ROM (optional, may not have this):

Used when upgrading IOS

 Cisco IOS

Normal operation, stored in Flash, runs in RAM

ITE PC v4.0

Router startup

ITE PC v4.0

‘Normal’ start up

1. Run POST and bootup instructions from ROM

2. Load IOS file from flash

3. Load configuration from NVRAM

4. Fully operational

ITE PC v4.0

Configuration register

 Has 4 hex digits – that’s 16 binary
digits

 Configuration register

is saved in
NVRAM

 show version to see its value

 Value of last hex digit tells how to
load IOS

 Usual is 0x2102 (2 means load
from flash)

 Third hex digit controls whether
configuration file is loaded. (0
means load, 4 means do not)

Check Configuration Register value (NVRAM)

0 = ROM Monitor mode

1 = ROM IOS

2 – 15 = Boot system from Flash

ITE PC v4.0

How a Cisco device locates and loads IOS

 Demo

config-register

The config-register can be Downloaded from:

http://www.lilligren.com/cisco/downloads.htm

ITE PC v4.0

Configuration register: 0, 1, and 2 and above

ITE PC v4.0

Configuration register: 2102 and 2142

ITE PC v4.0

Configuration register
Router(config)#config-register value

1 2

ITE PC v4.0

Loading IOS
 You see ############# as IOS loads from flash memory.

 If you see a prompt instead:

 rommon1>

 Then the IOS was not loaded and you are in ROM monitor mode.

 Try reload or boot

 If this fails, the IOS file is probably missing…

ITE PC v4.0

Configuration

 If there is a startup configuration file in NVRAM then it
will normally load into RAM as the running
configuration.

 If not, the router may look for a configuration on a TFTP
server. Wait until it gives up.

 It then prompts you to enter Setup mode: Would you
like to enter the initial configuration dialog? [yes/no]: no
(If it asks if you want to exit Autoinstall: yes)

ITE PC v4.0

Show version

 IOS version

 Bootstrap version

 Router model and CPU

 Amount of RAM

 Number and type of interfaces

 Amount of NVRAM

 Amount of Flash

 Configuration register

ITE PC v4.0

Basic Configuration (revision)

 Name

 Passwords

 Interfaces

 Routing

 Banner (Message of the day)



Save configuration

 Check configuration

ITE PC v4.0

Global configuration

 Router>enable

 Router#configure terminal (config t)

 Router(config)#

 Start in user exec mode

 Go to privileged exec mode (no configuration so no
password)

 Go to global configuration mode

ITE PC v4.0

Hostname

 Give the router a name to show at its prompt

 Do this in global configuration mode

 Router(config)# hostname ITT

 ITT(config)#

ITE PC v4.0

Enable secret

 Protect privileged exec mode with an encrypted
password.

 ITT(config)# enable secret class

 You could set an enable password but this is not
encrypted

 There is no need to set both, but if you do then the
enable secret will be used

ITE PC v4.0

Passwords for login

 Set login password on console port for security

 ITT(config)# line con 0

 ITT(config-line) password cisco

 ITT(config-line) login

 ITT(config-line) exit

 You can also put a password on the AUX port in a
similar way

ITE PC v4.0

Passwords for Telnet login

 Set login password on virtual lines to allow you to
Telnet to the router

 ITT(config)# line vty 0 4

 ITT(config-line) password cisco
 ITT(config-line) login
 ITT(config-line) exit

ITE PC v4.0

Interface configuration

 ITT(config)# interface serial 0

 ITT(config-if)# ip address 192.168.3.1 255.255.255.0

 ITT(config-if)# no shutdown

 ITT(config-if)# exit

 This is for a DTE serial interface

 Ethernet interfaces are configured the same way

ITE PC v4.0

Interface DCE configuration

 A DCE serial interface needs an extra line:

 ITT(config)# interface serial 0

 ITT(config-if)# ip address 192.168.3.1 255.255.255.0

 ITT(config-if)# clock rate 64000

 ITT(config-if)# no shutdown
 ITT(config-if)# exit

ITE PC v4.0

Interface description

 You can give an interface a description

 This does not affect the operation of the router but it is
useful documentation

 Do it in interface configuration mode for the required
interface

 ITT(config-if) description Serial line to Rocco 01993
876543

ITE PC v4.0

Message of the day

 You can configure a message to be shown before the
user logs on

 Cisco recommend that you show a warning to
unauthorized users (NOT “welcome”)

 ITT(config)# banner motd # authorized users only #

 # is a delimiter. Any character can be used.

ITE PC v4.0

Routing

 The router knows its directly attached networks
because you have put IP addresses on its interfaces

 It can put these networks in its routing table

 It needs to find routes to networks that are not directly
attached

 You can give it static routes

 You can enable a routing protocol

ITE PC v4.0

Routing protocol:

RIP

 You choose the routing protocol

 Then you tell the router which directly attached
networks it should advertise

 ITT(config) router rip

 ITT(config-router) network 192.168.1.0

 ITT(config-router) network 192.168.3.0

 ITT(config-router) exit

ITE PC v4.0

Save configuration

 Your configuration is held in RAM as the running
configuration

 If you want to keep this configuration then you must
save it to NVRAM into the startup configuration file

 ITT# copy running-config startup-config

ITE PC v4.0

Shortened commands

 The Cisco IOS accepts shortened forms of commands

 You need to type enough to distinguish the command
from other commands

 copy run start can be used instead of copy running-
config startup-config

 int s 0 can be used instead of interface serial 0

ITE PC v4.0

Show commands

 Show running-config

 Show startup-config



Show ip route

 Show ip interfaces

 Show ip interface brief

ITE PC v4.0

OSI layers 1, 2 and 3

Receive signals

from cable, convert

to binary.

Check layer 2

address,

decapsulate

Find destination network, check routing table for route,

direct packet to correct outgoing interface

Encapsulate with

frame for next link

Encode binary,

place signals on

cable

ITE PC v4.0

What the router does 1

 Ethernet frame received from PC1 through port Fa0/0

 Destination MAC address is router’s address

ITE PC v4.0

What the router does 2

 Strip off frame header and trailer (decapsulate)

 Read destination IP address 192.168.4.9

ITE PC v4.0

What the router does 3

 Logical AND with IP address 192.168.4.9 and subnet
mask 255.255.255.0 (/24) gives destination network
address 192.168.4.0

ITE PC v4.0

What the router does 4

 Look in routing table for network address 192.168.4.0

 Route found via 192.168.3.2 through S0/0

ITE PC v4.0

What the router does 5

 S0/0 connects to a WAN link using PPP

 Encapsulate packet in PPP frame

 Send frame out through S0/0

ITE PC v4.0

No route found

 If the destination network is not in the routing table:

 Use a default route if one exists

 Otherwise drop the packet and send an ICMP
destination unreachable message to the source host.

ITE PC v4.0

Routing tables

 A router uses the routing table to select the best path to
a network

 Directly connected networks are taken from the
interface configuration

 Static routes can be added by administrator

 Routes can be learned dynamically from other routers
by using a routing protocol

ITE PC v4.0

Show ip route

List of codes

List of routes

ITE PC v4.0

Routing table

C 192.168.1.0/24 is directly connected, FastEthernet0/0

C 192.168.2.0/24 is directly connected, Serial0/0

S 192.168.3.0/24 [1/0] via 192.168.2.2

R 192.168.4.0/24 [120/1] via 192.168.2.2, 00:00:20, Serial0/0

Directly connected
Network and mask

Exit port

ITE PC v4.0

Routing table
C 192.168.1.0/24 is directly connected, FastEthernet0/0
C 192.168.2.0/24 is directly connected, Serial0/0
S 192.168.3.0/24 [1/0] via 192.168.2.2
R 192.168.4.0/24 [120/1] via 192.168.2.2, 00:00:20, Serial0/0

Static route
Network and mask

Administrative

distance and metric
Address of next

hop router

ITE PC v4.0

Dynamic route, RIP
Network and mask

Administrative
distance and metric
Address of next

hop router
Time since

last update

Exit port

ITE PC v4.0

Static routes Dynamic routes

 Entered by administrator

 Time consuming, different for
each router

 Must be updated if routes
change

 Little processing

 No bandwidth used

 Gives nothing away

 Learned from other routers

 Start the protocol then it runs
by itself

 Automatically updates when
routes change

 More processing

 Uses bandwidth

 Gives away information

ITE PC v4.0

Routing protocols

Interior, used within

an organization’s

networks

Exterior, used

between different

organizations’

networks

BGP OSPF

IS-IS

Distance vector Link state

RIP

(IGRP)

EIGRP

Routing Information Protocol
Interior Gateway Routing Protocol
Enhanced Interior Gateway RP

Opens Shortest Path First
Intermediate System to…

Border Gateway Protocol

ITE PC v4.0

Routing Table Principles

1. Every router makes its decision alone, based on the
information it has in its own routing table.

2. The fact that one router has certain information in its
routing table does not mean that other routers have the
same information.

3. Routing information about a path from one network to
another does not provide routing information about the
reverse, or return, path.

ITE PC v4.0

Metrics

 A routing protocol may learn of several possible routes
to a destination.

 It uses metrics to pick the best route.

 RIP uses hop count as its only metric.

 OSPF uses “cost” based on bandwidth.

 EIGRP uses bandwidth and delay and can use load
and reliability as well.

ITE PC v4.0

Metrics

RIP uses hop count. It

picks this route as the

best.

ITE PC v4.0

Metrics

OSPF uses cost based

on bandwidth. It picks

this route as the best.

ITE PC v4.0

Administrative distance

 There may be more than one routing protocol running.
There may also be static routes.

 Static routes have administrative distance 1 or 0 by
default.

 RIP routes have administrative distance 120

 OSPF routes have administrative distance 110

 The route with the lowest administrative distance goes
in the routing table

ITE PC v4.0

Communicating over the
Network

Network Fundamentals – Chapter 2

Dr. C. BouSaba

Objectives

 Describe the structure of a network, including the
devices and media that are necessary for successful
communications.

 Explain the function of protocols in network
communications.

 Explain the advantages of using a layered model to
describe network functionality.

 Describe the role of each layer in two recognized
network models: The TCP/IP model and the OSI model.

 Describe the importance of addressing and naming
schemes in network communications.

Network Structure

 3 Common Elements of communication

1. message source

2. the channel

3. message destination

 Network definition
 data or information networks capable of carrying many different

types of communications (including traditional computer data,
interactive voice, video, and entertainment products).

 Messages are communicated by dividing the data sent across a
network in small manageable “chunks” called segments

Network Structure

Segmentation increases reliability

Network Structure
 Segmenting messages has 2 primary benefits:

1. By sending smaller individual pieces from source to
destination, many different conversations can be interleaved
on the network (multiplexing).

2. Segmentation increases the reliability of network. Segments
of each message need not travel same pathway across the
network from source to destination.

 If a path becomes congested with data traffic or fails, segments can
still be directed to destination using alternate pathways.

 If part of the message fails to make it to the destination, only the
missing parts need to be retransmitted.

 Segmenting messages has 1 disadvantage: increases the
level of complexity to the process.

Components of a network

 Devices

 Media

 Services

Are the physical elements or hardware

Are the communication programs or software,
running on the networked devices

Network Structure
 End Devices and their Role in the Network

– Form interface w/ human network & communications network

– Role of end devices depends on software installed on them:
a client, a server, or both

 End device, referred to as host, is either the source or destination of a
message transmitted over the network, and is identified by an address.

Network Structure
 Intermediary devices and their role in the network

– Provide connectivity and ensures data flows across network

– Use destination host address ( + info. about network interconnections),
to determine the path that messages should take through the network.

Intermediary network devices functions:

– Regenerate and retransmit data signals

– Maintain info. about existing pathways through network/internetwork

– Notify other devices of errors and communication failures

– Direct data along alternate pathways when there is a link failure

– Classify and direct messages according to QoS priorities

– Permit or deny the flow of data, based on security settings

 Network media is the channel over which a message travels

 Three media types:

1. Metallic wires within cables

2. Glass or plastic fibers (fiber optic cable)

3. Wireless transmission

Network Structure

 Different types of
network media have
different features and
benefits.

Network Structure
 The signal encoding that must occur for the message to be

transmitted is different for each media type.

1. On metallic wires, the data is encoded into electrical
impulses that match specific patterns.

2. Fiber optic transmissions rely on pulses of light, within
either infrared or visible light ranges.

3. In wireless transmission, patterns of electromagnetic
waves depict the various bit values.

 Criteria for choosing a network media are:

1. The distance the media can successfully carry a signal.

2. The environment in which the media is to be installed.

3. The amount of data and the transmission speed.

4. The cost of the media and installation

Network Types

 Local Area Networks (LANs)

– A network serving a home, building or campus is considered a (LAN)
Local Area Network and is usually administered by a single organization

 Wide Area Networks (WANs)

– Connect LANs that are separated by geographic distance

– Use a telecommunications service provider (TSP) to interconnect the
LANs at the different locations.

Network Types

 The Internet is defined as a global mesh of interconnected
networks

Network Types

Network Representations

How network devices and media connect to each
other?

 Network Interface Card – A NIC, or LAN adapter, provides the
physical connection to the network at the PC or other host
device. The media connecting the PC to the networking device
plugs directly into the NIC.

 Physical Port – A connector or outlet on a networking device
where the media is connected to a host or other networking
device.

 Interface – Specialized ports on an internetworking device that
connect to individual networks. Because routers are used to
interconnect networks, the ports on a router are referred to
network interfaces.

Function of Protocol in Network Communication

 A protocol is a set of predetermined rules

– facilitate communication over data networks

– is implemented in software and hardware that is loaded on each host
and network device.

 Successful communication between hosts on a network requires
the interaction of many different protocols.

 A protocol suite is a group of inter-related protocols that are
necessary to perform a communication function.

 Network protocols

Network protocols are used

to allow devices to

Communicate successfully

Function of Protocol in Network Communication

 Protocol suites and industry standards

A standard is

a process or protocol that has been endorsed by the
networking industry and ratified by a standards organization

Function of Protocol in Network Communication

 Application Protocol:

–HTTP governs the interaction between a web server and a web client.

–HTTP defines the content and formatting of the requests and responses

 Transport Protocol:

–TCP manages the conversations between web servers and web clients.

–TCP divides HTTP messages into smaller pieces, segments, to be sent to client.

–TCP controls the size and rate of exchanged messages between client/server.

 Internetwork Protocol:

–IP is responsible for taking the formatted segments from TCP, encapsulating
them into packets, assigning the appropriate addresses, and selecting the best
path to the destination host.

 Network Access Protocols: describe 2 primary functions, data link
management and the physical transmission of data on the media.

–Data-link management protocols take the packets from IP and format them to be
transmitted over the media.

–Physical media protocols govern how the signals are sent and how they are
interpreted. Transceivers on the network interface cards implement the appropriate
standards for the media that is being used.

Function of Protocol in Network Communication

 Technology independent Protocols

-Many diverse types of devices can communicate using the
same sets of protocols. This is because protocols specify
network functionality, not the underlying technology to support
this functionality.

Function of Protocol in Network Communication

Benefits of using a layered model
 Assists in protocol design

 Fosters competition

 Changes in one layer do not affect other layers

 Provides a common language

Layers with TCP/IP and OSI Model

 A protocol model provides

a model that closely
matches the structure of a
particular protocol suite.

– TCP/IP

 A reference model
provides a common
reference for maintaining
consistency within all
types of network protocols
and services.

– OSI (Open System
Interconnection)

TCP/IP Model

TCP/IP Communication Process

1. Creation of data at the Application layer of the originating source end device

2. Segmentation and encapsulation of data as it passes down the protocol stack
in the source end device

3. Generation of data onto the media at the Network Access layer of the stack

4. Transportation of the data through the internetwork, which consists of media
and any intermediary devices

5. Reception of data at the Network Access layer of the destination end device

6. Decapsulation and reassembly of the data as it passes up the stack in the
destination device

7. Passing this data to the destination application at the Application layer of the
destination end device

Protocol data units (PDU) and encapsulation

Process of sending and receiving messages

The OSI Model

Layers with TCP/IP and OSI Model

 Compare OSI and TCP/IP model

 Transport layer – responsible for low-level network access and for message
transfer between clients, including partitioning messages into packets,
maintaining packet order, controlling flow, and generating physical addresses

 Session layer – implements sessions, or process-to-process
communications protocols

 Presentation layer – resolves the differences in formats among the various
sites in the network, including character conversions, and half duplex/full
duplex (echoing)

 Application layer – interacts directly with the users: deals with file transfer,
remote-login protocols & email, as well as schemas for distributed databases

Communication Protocol
 Physical layer – handles the mechanical and electrical details of the physical

transmission of a bit stream

 Data-link layer – handles the frames, or fixed-length parts of packets,
including any error detection and recovery that occurred in the physical layer

 Network layer –provides connections & routes packets in the communication
network, including handling the address of outgoing packets, decoding the
address of incoming packets, & maintaining routing information for proper
response to changing load levels

Communication Via ISO Network Model

The ISO
Protocol

Layer

The ISO Network Message

Addressing and Naming Schemes

 Labels in encapsulation headers are used to manage
communication in data networks

Addressing and Naming Schemes

 Examples of Ethernet MAC Addresses, IP Addresses,
and TCP/UDP Port numbers

Addressing and Naming Schemes
 How labels in encapsulation headers are used to

manage communication in data networks

Addressing and Naming Schemes
 Information in the encapsulation header is used to

identify the source and destination processes for data
communication

Summary

ITE PC v4.0

Chapter 1 1

Static Routing

Routing Protocols and Concepts – Chapter 2

ITE PC v4.0

Topics

 Role of the router in

networks

 Directly connected networks and interfaces

 CDP protocol

 Static routes with exit interfaces

 Summary and default routes

 Forwarding with static routes

 Managing and troubleshooting static routes

ITE PC v4.0

WAN Serial connections

Smart serial

connector to router

V35 DTE connection to

ISP CSD/DSU device

Larger DB-60

for older routers

Four other standards possible –

choose the right cable.

http://www.csdata.com/csdonline/customer/product.php?productid=18217&cat=314&page=1

ITE PC v4.0

A WAN Physical Layer connection has sides:

Data Circuit-terminating Equipment (DCE) – This is the service provider.
CSU/DSU is a DCE device.

 The CSU/DSU (DCE device) is used to convert the data from the router (DTE device)
into a form acceptable to the WAN service provider.

a DCE device such as a CSU/DSU will provide the clock.

Data Terminal Equipment (DTE) – Typically the router is the DTE device.

Up-to-date technology

Cisco 1-Port T1/Fractional T1 DSU/CSU

WAN Interface Card (WIC-1DSU-T1-V2=)

WAN Serial connections

ITE PC v4.0

LAN Ethernet connections

 Connections of a Router for WAN

-A router has a DB-60 port that can
support 5 different cabling standards

–Newer routers support the smart serial
interface that allows for more data to be
forwarded across fewer cable pins.

 Connections of a Router for Ethernet

-2 types of connectors can be used:
Straight through and Cross-over

Straight through used to connect:

-Switch-to-Router, Switch-to-PC, Hub-
to-PC, Hub-to-Server

Cross-over used to connect (pin 1
connected to pin 3, and pin 2 connected to
pin 6):

-Switch-to-Switch, PC-to-PC, Switch-to-
Hub, Hub-to-Hub, Router-to-Router,
PC-Router

ITE PC v4.0

Default Condition

 By default, interfaces have no IP addresses and are
administratively shut down.

 They need to be configured.

ITE PC v4.0

Configure interface

R1(config)#interface fastethernet 0/0

R1(config-if)#

ip address 172.16.3.1 255.255.255.0

R1(config-if)#no shutdown

*Mar 1 01:16:08.212: %LINK-3-UPDOWN: Interface
FastEthernet0/0, changed state to up

*Mar 1 01:16:09.214: %LINEPROTO-5-UPDOWN: Line
protocol on Interface FastEthernet0/0, changed state to up

ITE PC v4.0

Check interfaces

R1#show interfaces fastethernet 0/0

FastEthernet0/0 is up, line protocol is up

Hardware is AmdFE, address is 000c.3010.9260

Internet address is 172.16.3.1/24 etc.

 Note MAC address of Ethernet interface

 Interface takes part in ARP with its network and keeps an
ARP table

ITE PC v4.0

Check interfaces

R1#show run

interface FastEthernet0/0

ip address 172.16.3.1 255.255.255.0

(Does not say no shutdown)

ITE PC v4.0

Interface not up?

 If the interface does not come up – check the cable,
check link lights, check the configuration at the other
end.

 If the protocol does not come up – for Ethernet check
that you have the right cable (straight-through or
crossover) – for serial check that the clock rate is on
the right end of the cable, check that the same Layer 2
protocol is used.

ITE PC v4.0

Directly connected

 Configure IP address on interface

 It appears in routing table

 Note subnetting information

ITE PC v4.0

Serial interface

 R2(config)#interface serial 0/0

 R2(config-if)#ip address 172.16.2.2 255.255.255.0

 R2(config-if)#no shutdown

 This is DTE end

 DCE end needs an additional command

 R3(config-if)#clock rate 64000

ITE PC v4.0

Usual show commands

 Check that interface and protocol are up

show interfaces

show ip interface brief

show running-config

 Check that network is in routing table

show ip route

ITE PC v4.0

Show controllers

R1#show controllers serial 0/0

Interface Serial0/0

Hardware is PowerQUICC MPC860

DCE V.35, no clock etc.

 Shows if a cable is connected

 Shows the type of cable

 Shows if clock rate set

ITE PC v4.0

debug ip routing

 R2#debug ip routing

 If you give this command before configuring the
interfaces then you see a report of the networks being
added to the routing table.

 R2#no debug ip routing or
R2#no debug all

 Switch off debugging as soon as possible after use – it
takes up resources.

ITE PC v4.0

Cisco Discovery Protocol

 Works at layer 2

 Directly connected devices only

 Cisco devices only

 Devices send CDP advertisements to neighbors at
regular intervals

 Use it to find out about networking devices

ITE PC v4.0

Show cdp neighbors

 Does not show IP address

 You need show cdp neighbors detail for that.

ITE PC v4.0

Going further

 CDP only shows immediate neighbors, but it does tell
you their IP addresses.

 Telnet to the neighbor and then use CDP to find out
about its neighbors and so on.

ITE PC v4.0

Disable CDP

 Disable CDP for the entire device:

 Router(config)#no cdp run

 Stop CDP advertisements on one interface:

 Router(config-if)#no cdp enable

 Do this for security.

ITE PC v4.0

Static routes

 Use for stub networks: only one entry.

Stub network

networks

Static route

Default route

ITE PC v4.0

Configure a static route

 R1(config)#ip route 172.16.1.0 255.255.255.0

172.16.2.2

 Give the next hop address

 R1(config)#ip route 172.16.1.0 255.255.255.0 Serial 0/0

 Or give the exit interface

ITE PC v4.0

Show ip route

 Routing table now includes:

 S 172.16.1.0 /24 [1/0] via 172.16.2.2

 Or
S 172.16.1.0 /24 is directly connected, serial 0/0

 Administrative distance 1

 Metric 0

ITE PC v4.0

Return route

 If you use static routing, you need to configure
static routes in both directions.

 A route in one direction does not ensure that there
is a route in the other direction.

ITE PC v4.0

Find a route to 172.16.1.0/24

Recursive lookup

There it is, via

172.16.2.2

How do you get to

172.16.2.2?

There it is via serial 0/0.

ITE PC v4.0

Static route giving interface

 R1(config)#ip route 192.168.2.0 255.255.255.0 serial 0/0

ITE PC v4.0

Interface down

 If the interface used by a static route goes down, then
the static route is removed from the routing table.

 The static route remains in the configuration.

 If the interface comes up again then the static route
goes back in the routing table.

ITE PC v4.0

Delete a static route

 R1(config)#no ip route 192.168.2.0 255.255.255.0
serial 0/0

 Give the same command again with no in front.

 Most commands can be reversed like this.

ITE PC v4.0

Next hop or exit interface?

 For a point to point serial link, configure the static route
with the exit interface.

Only one look-up, less processing.

 For an Ethernet link, configure the static route with the
next hop address (or with both).

This identifies the device that should receive the packet next.
The MAC address can be found and used in the frame header.

ITE PC v4.0

Summarizing static routes

ITE PC v4.0

Default route

 All packets from the stub network need to go on the
same route to the right hand router.

 Configure a static default route.

Stub network
networks
Static route
Default route

ITE PC v4.0

Configure a default route

 Router(config)#ip route 0.0.0.0 0.0.0.0 serial 0/0
Using exit interface.

 Router(config)#ip route 0.0.0.0 0.0.0.0 172.16.2.2
Using next hop address

 0.0.0.0 network address and subnet mask is called
quad zero. It matches anything.

ITE PC v4.0

Routing table

 S* 0.0.0.0/0 is directly connected, Serial0/0

 The default route is shown with a *

ITE PC v4.0

Troubleshooting tools

 ping

 traceroute

 show ip route

 show ip interface brief

 show cdp neighbors

 show running-config

ITE PC v4.0

General Role of the Router

ITE PC v4.0

General Role of the Router

 Connections of a Router for WAN

-A router has a DB-60 port that can support 5 different cabling standards

 Connections of a Router for Ethernet

-2 types of connectors can be used: Straight through and Cross-over

Straight through used to connect:

-Switch-to-Router, Switch-to-PC, Router-to-Server, Hub-to-PC, Hub-to-
Server

Cross-over used to connect:

-Switch-to-Switch, PC-to-PC, Switch-to-Hub, Hub-to-Hub, Router-to-
Router

 Functions of a Router

Best Path Selections

Forwarding packets to destination

ITE PC v4.0

Interfaces

 Examining Router

Interfaces

-Show IP router command – used to view routing table

-Show Interfaces command – used to show status of an interface

-Show IP Interface brief command – used to show a portion of the
interface information

-Show running-config command – used to show configuration file in RAM

 Configuring an Ethernet interface

-By default all serial and Ethernet interfaces are down

-To enable an interface use the No Shutdown command

 Verifying Ethernet interface

-Show interfaces for fastEthernet 0/0 – command used to show status of
fast Ethernet port

-Show ip interface brief

-Show running-config

 Ethernet interfaces participate in ARP

ITE PC v4.0

 Configuring a Serial interface

-Enter interface configuration mode

-Enter in the ip address and subnet mask

-Enter in the no shutdown command

 Example:

-R1(config)#interface serial 0/0

-R1(config-if)#ip address 172.16.2.1 255.255.255.0

-R1(config-if)#no shutdown

Interfaces

ITE PC v4.0

 Examining Router Interfaces

-Physically connecting a WAN Interface.

-A WAN Physical Layer connection has sides:

Data Circuit-terminating Equipment (DCE) – This is the service
provider. CSU/DSU is a DCE device.

Data Terminal Equipment (DTE) – Typically the router is DTE device.

Interfaces

 Configuring serial links in a lab environment

One side of a serial connection must be considered a DCE

This requires placing a clocking signal – use the clock rate command.

Example:

-R1(config)#interface serial 0/0

-R1(config-if)#clockrate 64000

Serial Interfaces require a clock signal to control the timing of the
communications.

ITE PC v4.0

Routing Table and CDP Protocol

 Purpose of the debug ip routing command

Allows viewing changes that the router performs when adding or
removing routes

Example:

-R2#debug ip routing

-IP routing debugging is on

 To configure an Ethernet interface

Example:

-R2(config)#interface fastethernet 0/0

-R2(config-if)#ip address 172.16.1.1 255.255.255.0

-R2(config-if)#no shutdown

ITE PC v4.0

Routing Table and CDP Protocol

 When a router only has its interfaces configured & no other
routing protocols are configured then:

-The routing table contains only the directly connected networks

-Only devices on the directly connected networks are reachable

ITE PC v4.0

 Checking each route
in turn

The ping command is
used to check end to
end connectivity

ITE PC v4.0

Routing Table and CDP Protocol

 Purpose of CDP

A layer 2 cisco proprietary tool used to gather information about other
directly connected Cisco devices.

 Concept of neighbors

-2 types of neighbors

Layer 3 neighbors

Layer 2 neighbors

ITE PC v4.0

Routing Table and CDP Protocol

 CDP show commands

Show cdp neighbors command

-Displays the following information:

Neighbor device ID

Local interface

Holdtime value, in seconds

Neighbor device capability code

Neighbor hardware platform

Neighbor remote port ID

Show cdp neighbors detail command

-Useful in determining if an IP address configuration error

 Disabling CDP

To disable CDP globally use the following command

Router(config)#no cdp run

ITE PC v4.0

Static Routes with Exit Interfaces

 Purpose of a static route

A manually configured route used when routing from a net to a stub net

 IP route command

To configure a static route use the following command: ip route

ITE PC v4.0

Static Routes with Exit Interfaces

ITE PC v4.0

 Dissecting static route syntax

ip route – Static route command

172.16.1.0 – Destination network address

255.255.255.0 – Subnet mask of destination network

172.16.2.2 – Serial 0/0/0 interface IP address on R2, which is the “next-
hop” to this network

Static Routes with Exit Interfaces

 Configuring routes to 2 or more remote networks

Use the following commands for R1

-R1(config)#ip route 192.168.1.0 255.255.255.0 172.16.2.2

-R1(config)#ip route 192.168.2.0 255.255.255.0 172.16.2.2

ITE PC v4.0

Static Routes with Exit Interfaces

ITE PC v4.0

Static Routes with Exit Interfaces

Zinin’s 3 routing principles

Principle 1: “Every router makes its decision alone,
based on the information it has in its own routing
table.“

Principle 2: “The fact that one router has certain
information in its routing table does not mean that
other routers have the same information.“

Principle 3: “Routing information about a path from
one network to another does not provide routing
information about the reverse, or return path.”

ITE PC v4.0

Static Routes with Exit Interfaces

 Using Zinin’s 3 routing principles, how would you answer the
following?

-Would packets from PC1 reach their destination?

Yes, packets destined for 172.16.1.0/24 and 192.168.1.0/24 networks
would reach their destination.

-Does this mean that any packets from these networks destined for
172.16.3.0/24 network will reach their destination?

No, because neither R2 nor R3 router has a route to the 172.16.3.0/24
network.

ITE PC v4.0

Static Routes with Exit Interfaces

 Resolving to an Exit Interface

-Recursive route lookup – Occurs when the router has to perform
multiple lookups in the routing table before forwarding a packet. A static
route that forwards all packets to the next-hop IP address goes through the
following process (reclusive route lookup)

The router first must match static route’s destination IP address with
the Next hop address

The next hop address is then matched to an exit interface

ITE PC v4.0

 Configuring a Static route with an Exit Interface

-Static routes configured with an exit interface are more efficient because
the routing

–The routing table can resolve the exit interface in a single search instead
of 2 searches

-Example of syntax require to configure a static route with an exit interface

Static Routes with Exit Interfaces

ITE PC v4.0

 Modifying Static routes

Existing static routes cannot be modified. The old static route must be
deleted by placing no in front of the ip route

Example:

-no ip route 192.168.2.0 255.255.255.0 172.16.2.2

A new static route must be rewritten in the configuration

Static Routes with Exit Interfaces

ITE PC v4.0

 Verifying the Static Route Configuration

-Use the following commands

Step 1 show running-config

Step 2 verify static route has been entered correctly

Step 3 show ip route

Step 4 verify route was configured in routing table

Step 5 issue ping command to verify packets can reach destination
and that Return path is working

Static Routes with Exit Interfaces

ITE PC v4.0

 Ethernet interfaces and ARP.

– If a static route is configured on an Ethernet link

-If the packet is sent to the next-hop router then…

the destination MAC address will be the
address of the next hop’s Ethernet interface

This is found by the router consulting the
ARP table.

If an entry isn’t found then an ARP
request will be sent out

Static Routes with Exit Interfaces

ITE PC v4.0

Summary and Default Route

 Summarizing routes reduces the size of the routing table.

 Route summarization is the process of combining a number of
static routes into a single static route.

 Configuring a summary route

Step 1: Delete the current static route

Step 2: Configure the summary static route

Step 3: Verify the new static route

ITE PC v4.0

Summary and Default Route

ITE PC v4.0

Summary and Default Route
 Default Static Route

This is a route that will match all packets. Stub routers that have a
number of static routes all exiting the same interface are good candidates
for a default route.

-Like route summarization this will help reduce the size of routing table

 Configuring a default static route

Similar to configuring a static route. Except that destination IP address
and subnet mask are all zeros

Example:

-Router(config)#ip route 0.0.0.0 0.0.0.0 [exit-interface | ip-address ]

 Static routes and subnet masks

The routing table lookup process will use the most specific match when
comparing destination IP address and subnet mask

 Default static routes and subnet masks

Since the subnet mask used on a default static route is 0.0.0.0 all packets
will match.

ITE PC v4.0

Static Routes and Packet Forwarding

 Packet forwarding
with static routes.
(recall Zinin’s 3
routing principles)

 Router 1

Packet arrives on R1’s
Fastethernet 0/0
interface

R1 does not have a
route to the
destination
network,
192.168.2.0/24

R1 uses the default

static route.

ITE PC v4.0

 Packet forwarding with static routes. (Zinin’s 3 routing principles)

 Router 2

The packet arrives on the Serial 0/0/0 interface on R2.

R2 has a static route to 192.168.2.0/24 out Serial0/0/1.

Static Routes and Packet Forwarding

ITE PC v4.0

 Packet forwarding with static routes. (Zinin’s 3 routing principles)

 Router 3

The packet arrives on the Serial0/0/1 interface on R3.

R3 has a connected route to 192.168.2.0/24 out Fastethernet 0/1.

Static Routes and Packet Forwarding

ITE PC v4.0

 Troubleshooting a Missing Route

 Tools that can be used to isolate routing problems include:

-Ping– tests end to end connectivity

-Traceroute– used to discover all of the hops (routers) along the path
between 2 points

-Show IP route– used to display routing table & ascertain forwarding
process

-Show ip interface brief- used to show status of router interfaces

-Show cdp neighbors detail– used to gather configuration information
about directly connected neighbors

Static Routes and Packet Forwarding

ITE PC v4.0

 Solving a Missing Route

 Finding a missing or mis-configured route requires methodically
using the correct tools

-Start with PING. If ping fails then use traceroute to determine where
packets are failing to arrive

 Issue: show ip route to examine routing table.

-If there is a problem with a mis-configured static route remove the static
route then reconfigure the new static route

Static Routes and Packet Forwarding

ITE PC v4.0

 Solving a Missing Route
Static Routes and Packet Forwarding

ITE PC v4.0

Static Routes and Packet Forwarding
 Solving a Missing Route

ITE PC v4.0

Summary
 Routers

-Operate at layer 3

-Functions include best path selection & forwarding packets

 Connecting Networks

WANs

Serial cables are connected to router serial ports.

In the lab environment clock rates must be configured for DCE

LANs

Straight through cables or cross over cables are used to connect to
fastethernet port. (The type of cable used depends on what devices
are being connected)

 Cisco Discovery Protocol

A layer 2 proprietary protocol

Used to discover information about directly connected Cisco devices

ITE PC v4.0

Summary
 Static Routes

-This is a manually configured path that specifies how the router will get to
a certain point using a certain path.

 Summary static routes

-This is several static routes that have been condensed into a single static
route.

 Default route

-It is the route packets use if there is no other possible match for their
destination in the routing table.

 Forwarding of packets when static route is used

-Zinin’s 3 routing principles describe how packets are forwarded

 Troubleshooting static routes may require some of the following
commands

-Ping

-Traceroute

-Show IP route

-Show ip interface brief

-Show cdp neighbors detail

ITE PC v4.0

rights reserved. Cisco Public 1

Application Layer
Functionality and
Protocols

Network Fundamentals – Chapter 3

Dr. C. BouSaba

OSI Reference Model

 The OSI reference model is a layered,
abstract representation created as a
guideline for network protocol design.

– Divides the networking process into
7 logical layers.

– Each layer has unique functionality &
is assigned specific services & protocols.

info is passed starting at Application
L down the hierarchy to Physical L

O
p

e
n

S
y
s
te

m
s
In

te
rc

o
n

n
e

c
tio

OSI: The Application Layer

info is passed over the network to destination host, where the
info proceeds back up the hierarchy, ending at Application L.

OSI: The Application Layer

OSI & TCP/IP: The Application Layers

The TCP/IP application layer protocols fit roughly into the framework of the
top 3 layers of the OSI model: Application, Presentation & Session layers.

 The Application layer,

–Layer seven, is the top layer of both the OSI and TCP/IP models.

–Provides the interface between applications we use to communicate
and the underlying network over which our messages are transmitted.

–Application layer protocols are used to exchange data between
programs running on the source and destination hosts.

OSI: The Application Layer – 7

 The Presentation Layer has three primary functions:

1. Coding and conversion of Application layer data to ensure that
data from the source device can be interpreted by the appropriate
application on the destination device.

2. Compression of the data in a manner that can be decompressed by
the destination device.

3. Encryption of the data for transmission and the decryption of data
upon receipt by the destination.

 Examples include:

QuickTime: an Apple specification for video & audio,

Motion Picture Experts Group (MPEG):
a standard for video compression and coding.

Graphics Interchange Format (GIF),

Joint Photographic Experts Group (JPEG),

Tagged Image File Format (TIFF)
GIF & JPEG are compression & coding standards for graphic images.

TIFF is a standard coding format for graphic images.

OSI: The Presentation Layer – 6

 The Session Layer create and maintain dialogs between
source and destination applications.

The Session layer handles the exchange of info to initiate dialogs, keep
them active, and to restart sessions that are disrupted or idle for a long
period of time.

 Most applications, like web browsers or e-mail clients,
incorporate functionality of the OSI layers 5, 6 and 7.

OSI: The Session Layer – 5

 The widely-known Application layer protocols provide exchange of info

 Among these TCP/IP protocols are:

Domain Name Service Protocol (DNS) is used to resolve Internet names to IP
addresses.

Hypertext Transfer Protocol (HTTP) is used to transfer files that make up the Web
pages of the World Wide Web.

Simple Mail Transfer Protocol (SMTP) is used for the transfer of mail messages
and attachments.

Telnet, a terminal emulation protocol, is used to provide remote access to servers
and networking devices.

File Transfer Protocol (FTP) is used for interactive file transfer between systems.

 The protocols in the TCP/IP suite are generally defined by Requests

for Comments (RFCs).

The Internet Engineering Task Force maintains the RFCs as the standards for the
TCP/IP suite.

TCP/IP: The Application Layer

Application Layer Software

 The functions associated with the Application layer protocols
enable humans to interface with the underlying data network.

 There are two forms of software programs or processes that
provide access to the network: applications and services.

1. Network-Aware Applications

Applications are the software programs used by people to communicate over
the network.

E-mail clients and web browsers are examples of these types of applications.

2. Application layer Services

Other programs may need the assistance of Application layer services to use
network resources, like file transfer or network print spooling.

Though transparent to the user, these services are the programs that interface
with the network and prepare the data for transfer.

Application Layer Software

User Applications, Services and Application Layer Protocols

 In the OSI model, applications that interact directly with people are
considered to be at the top of the stack, as are the people themselves.

 The Application layer uses protocols that are implemented within
applications and services.

–Applications provide people with a way to create messages

–Application layer services establish an interface to the network

–Protocols provide the rules and formats that govern how data is treated.

 All three components may be used by a single executable program and
may even use the same name.

For example, when discussing “Telnet” we could be referring to the application,
the service, or the protocol.

User Applications, Services and Application Layer Protocols

Application Layer Protocol Functions

 Application layer protocols are
used by both source &
destination devices during a
communication session.

If the communications to be
successful, the application
layer protocols implemented
on the source and destination
host must match.

 Application layer protocols functions:

•Protocols establish consistent rules for exchanging data between
applications and services loaded on the participating devices.

•Protocols specify how data inside the messages is structured and the
types of messages that are sent between source and destination.

•These messages can be requests for services, acknowledgments, data,
status, or error messages.

•Protocols also define message dialogues, ensuring that a message
being sent is met by the expected response when data transfer occurs.

•Applications and services may also use multiple protocols in the course
of a single conversation.

•One protocol may specify how to establish the network connection and
another describe the process for the data transfer when the message is
passed to the next lower layer.

Application Layer Protocol Functions

The Client-Server Model

 Client and server processes are considered to be in the Application layer.

the device requesting the information is called a client

the device responding to the request is called a server.

Application layer protocols describe the format of the requests and responses
between clients and servers.

 One example of a client/server network is a corporate environment where
employees use a company e-mail server to send, receive and store e-mail.

The e-mail client on an employee computer issues a request to the e-mail server
for any unread mail.

The server responds by sending the requested e-mail to the client.

 Data is typically flowing from the server to the client, some data always
flows from the client to the server.

A client may transfer a file to the server for storage purposes (upload).

Data from a server to a client as a download.

The Client-Server Model

Servers

 Any device that responds to requests from client applications is functioning as
a server.

A server is usually a computer that contains information to be shared with many
client systems.

For example, web pages, documents, databases, pictures, video, and audio files
can all be stored on a server and delivered to requesting clients.

In other cases, such as a network printer, the print server delivers the client print
requests to the specified printer.

Some servers may require authentication of user account information to verify if
the user has permission to access the requested data or to use a particular
operation.

 In a client/server network, the server
runs a service, or process, is called
a server daemon.

–Daemons typically run in the
background and are not under an
end user’s direct control.

–Daemons are “listening” for a
request from a client, because they
are programmed to respond
whenever the server receives a
request for the service provided by
the daemon.

–When a daemon “hears” a request
from a client, it exchanges
appropriate messages with the client
and proceeds to send the requested
data to the client in the proper format.

Servers

Application Layer Services and Protocols

 A single application may employ many different supporting
Application layer services;

thus what appears to the user as one request for a web page may, in
fact, amount to dozens of individual requests.

And for each request, multiple processes may be executed.

For example, a client may require several individual processes to
formulate just one request to a server.

 Additionally, servers typically have multiple clients requesting
information at the same time.

For example, a Telnet server may have many clients requesting
connections to it simultaneously

The Application layer processes and services rely on support from lower
layer functions to successfully manage the multiple conversations.

 A single application may employ many different supporting
Application layer services;

Demo:

http://www.cnn.com

Application Layer Services and Protocols

The Peer-to-Peer Model

 Peer-to-peer networking involves two distinct forms: peer-to-peer network
design and peer-to-peer applications (P2P).

 Peer-to-Peer Networks
In a peer-to-peer network, two or more computers are connected via a network
and can share resources (such as printers) without having a dedicated server.

Every connected end device (known as a peer) can function as either a server or
a client.

One computer might assume the role of server for one transaction while
simultaneously serving as a client for another.

 A simple home network with two computers sharing a printer is an example
of a peer-to-peer network.

Each person can set his or her computer to share files, enable networked
games, or share an Internet connection.

 Because peer-to-peer networks usually do not use centralized user
accounts, permissions, or monitors

it is difficult to enforce security

Peer-to-Peer Networking

The Peer-to-Peer Model

 Peer-to-Peer (P2P) Applications
Allow a device to act as both a client and a server within the same
communication.

Require that each end device provide a user interface and run a background
service.

When a specific P2P application is launched, it invokes the required user
interface and background services.

 Some P2P applications use a hybrid system where resource sharing is
decentralized but the indexes that point to resource locations are stored in
a centralized directory.

In a hybrid system, each peer accesses an index server to get the location of a
resource stored on another peer.

The index server can also help connect two peers, but once connected, the
communication takes place between the two peers without additional
communication to the index server.

 Peer-to-peer applications can be used on peer-to-peer networks,
client/server networks, and across the Internet.

Peer-to-Peer Applications

Services and Protocol: Port Number

 Port numbers identify applications and Application layer services that are
the source and destination of data.

Server programs generally use predefined port numbers known by clients.

 Some of these services are:

File Transfer Protocol (FTP) – TCP Ports 20 and 21

Telnet – TCP Port 23

Simple Mail Transfer Protocol (SMTP) – TCP Port 25 (Is a long established
Internet protocol that is used for the delivery and receipt of e-mail).

Domain Name System (DNS) – TCP/UDP Port 53 (TCP is used for “zone
transfers” of full name record databases, while UDP is used for individual
lookups.)

Dynamic Host Configuration Protocol – UDP Port 67

Hypertext Transfer Protocol (HTTP) – TCP Port 80

Post Office Protocol (POP) – UDP Port 110 (Is only to collect e-mail)

Services and Protocol: Port Number

Services and Protocol: Port Number
 Dynamic Host Configuration Protocol – UDP Port 67 and 68

 When a system starts up on a network it must first request an IP address (assume it is not
using a static IP address), and it does this by broadcasting a request to the DHCP server:

 UDP 0.0.0.0:68 -> 255.255.255.255:67

since the requesting system doesn’t have an IP address (why it is asking) it uses 0.0.0.0 and since
its new to the network it doesn’t know where the DHCP server is, so it broadcasts the request to the
entire network (255.255.255.255).

 The DHCP server then responds with something like:

 UDP 192.168.1.1:67 -> 255.255.255.255:68

This is typically a DHCP offer. NOTE it has to be broadcasted (255.255.255.255) as the requesting
system doesn’t yet have an IP address (its contained in the offer). The data in this transmission
contains the IP and other network configuration information that the requesting system needs to
connect to the network (lease time, Subnet Mask, etc).

 Sometimes you will see something like:

 UDP 192.168.1.101:67 -> 192.168.1.1:68

as a request, followed by a reply

 UDP 192.168.1.1:68 -> 192.168.1.101:67

These are typically IP renewal requests, where a system has an IP address and is asking to renew it
(ie get the lease extended). Since the requesting system knows where the DHCP server is and it
already has a current IP address the requests don’t need to use 0.0.0.0 and 255.255.255.255.

 Devices are labeled with numeric IP addresses, so that they can participate in
sending and receiving messages over the network.

People have a hard time remembering this numeric address.

Domain names were created to convert the numeric address into a simple, recognizable
name.

 On the Internet these domain names, such as www.cisco.com, are much easier for
people to remember than 198.133.219.25, the actual address for this server.

Also, if Cisco decides to change the numeric address, it is transparent to the user, since
the domain name will remain www.cisco.com.

The new address will simply be linked to the existing domain name and connectivity is
maintained.

 The

DNS

was created for domain name to address resolution for these networks.

DNS uses a distributed set of servers to resolve the names associated with these
numbered addresses.

DNS

DNS Services and Protocol

 DNS is a client/server service;

The DNS client, or DNS resolver, supports name resolution for other network applications and
services that need it.

 nslookup is an OS utility that allows the user to manually query the name servers to
resolve a given host name.

This utility can also be used to troubleshoot name resolution issues and to verify the current
status of the name servers.

DNS Services and Protocol

 A DNS server provides the name resolution
using the name daemon, which is often
called named, (pronounced name-dee).

 The DNS server stores different types of
resource records used to resolve names.
These records contain the name, address,
and type of record.

 Some of these record types are:

A – an end device address

NS – an authoritative name server

CNAME – canonical name (or Fully Qualified
Domain Name) for an alias; used when
multiple services have single network address
but each service has its own entry in DNS

MX – mail exchange record; maps a domain
name to a list of mail exchange servers for
that domain

 When a client makes a query, the server’s “named” process
first looks at its own records to see if it can resolve the name.

If it is unable to resolve the name it contacts other servers to resolve the
name.

The request take extra time and consume bandwidth.

Once a match is found and returned to the original requesting server,
the server temporarily stores the numbered address that matches the
name in cache.

If that same name is requested again, the first server can return the
address by using the value stored in its name cache.

Caching reduces both the DNS query data network traffic and the workloads
of servers higher up the hierarchy.

DNS Services and Protocol

D
N

S
S

e
rv

ic
e
s

a
n

d
P

ro
to

c
o

 The Domain Name System uses a hierarchical system to create a name
database to provide name resolution.

The hierarchy looks like an inverted tree with the root at the top and branches
below.

The root servers maintain records about how to reach the top-level domain
servers, which in turn have records that point to the secondary level domain
servers and so on.

 Examples of top-level domains are:

.au – Australia

.com – a business or industry

.org – a non-profit organization

DNS Services and Protocol

WWW Service and HTTP

 When a web address (or URL) is typed into a web browser, the web browser
establishes a connection to the web service running on the server using the
HTTP protocol.

The http://www.cisco.com/index.html example

http (the protocol or scheme)

www.cisco.com (the server name)

A web page named index.html on a server.

The browser then checks with a name server to convert www.cisco.com into a
numeric address, which it uses to connect to the server.

Using the HTTP protocol, the browser sends a GET request to the server asks for
file index.html.

The server in turn sends the HTML code for this web page to the browser.

Finally, the browser deciphers the HTML code and formats the page for the
browser window.

Other types of data, may require another service or program, typically referred to as plug-
ins

WWW Service and HTTP

 The Hypertext Transfer Protocol (HTTP), one of the most used
application protocols.

 HTTP specifies a request/response protocol. The three
common message types are GET, POST, and PUT.

GET is a client request for data. A web browser sends the GET message
to request pages from a web server.

Once the server receives the GET request, it responds with a status line,
such as HTTP/1.1 200 OK, and a message of its own, the body of which may
be the requested file.

POST and PUT are used to send messages that upload data to the web
server.

For example, when the user enters data into a form embedded in a web
page, POST includes the data in the message sent to the server.

PUT uploads resources or content to the web server.

WWW Service
and HTTP

 HTTP is not a secure protocol.

The POST messages upload information to the server in plain text that
can be intercepted and read.

Similarly, the server responses, typically HTML pages, are also
unencrypted.

 For secure communication across the Internet, the HTTP
Secure (HTTPS) protocol is used for accessing or posting web
server information.

HTTPS can use authentication and encryption to secure data as it
travels between the client and server.

HTTPS specifies additional rules for passing data between the
Application layer and the Transport Layer.

WWW Service and HTTP

E-mail Service and SMTP/POP Protocols
 E-mail, the most popular network service, has revolutionized how people

communicate through its simplicity and speed.

 To run on a computer or other end device, e-mail requires several
applications and services.

Post Office Protocol (POP): the e-mail client can use POP.

Simple Mail Transfer Protocol (SMTP):
define the formats and commands
used to send e-mail from either
a client or a server.

 When people compose e-mail
messages, they typically use an
application called a Mail User
Agent (MUA), or e-mail client.

The MUA allows messages to be
sent and places received
messages into the client’s mailbox.

E-mail Server Processes – MTA and MDA

 E-mail Server Processes – MTA and MDA

 The e-mail server operates two separate processes:

Mail Transfer Agent (MTA)

The MTA process is used to
forward e-mail.

The MTA receives messages
from the MUA or from another
MTA on another e-mail server.
Based on the message header,
it forwarded to reach its
destination.

Mail Delivery Agent (MDA)

If the mail is addressed to
a user whose mailbox is on
the local server, the mail is
passed to the MDA.

E-mail Server Processes – MTA and MDA
 MDA accepts an e-mail from a MTA and performs the actual delivery.

The MDA can also resolve final delivery issues, such as virus scanning,
spam filtering, and return-receipt handling.

 There are other alternatives for e-mail delivery.

A client may be connected to a corporate e-mail system, such as IBM’s Lotus
Notes, Novell’s Groupwise, or Microsoft’s Exchange.

Computers that do not have an MUA can still connect to a mail service on a web
browser in order to retrieve and send messages in this manner.

 E-mail can use the POP and SMTP

POP3 are inbound mail delivery protocols. They deliver e-mail from the e-mail
server to the client (MUA).

The MDA listens for when a client connects to a server. Once a connection is
established, the server can deliver the e-mail to the client.

The SMTP, transfer of outbound e-mail from the sending client to the e-mail
server (MDA), as well as the transport of e-mail between e-mail servers (MTA).

SMTP enables e-mail to be transported across data networks between different types
of server and client software and makes e-mail exchange over the Internet possible.

E-mail Server
Processes –
MTA and MDA

E-mail Server Processes – MTA and MDA

http://mail.google.com/support/bin/answer.py?answer=76147

E-mail Server Processes – MTA and MDA

 The SMTP protocol message format uses a rigid set of commands and
replies.

These commands support the procedures used in SMTP, such as session
initiation, mail transaction, forwarding mail, verifying mailbox names, expanding
mailing lists, and the opening and closing exchanges.

 Some of the commands specified in the SMTP protocol are:

HELO – identifies the SMTP client process to the SMTP server process

EHLO – Is a newer version of HELO, which includes services extensions

MAIL FROM – Identifies the sender

RCPT TO – Identifies the recipient

DATA – Identifies the body of the message

File Transfer Protocol (FTP)

 The FTP is a Application layer protocol.

FTP allows for file transfers between a client and a server.

An FTP client is an application that runs on a computer that is used to
push and pull files from a FTP server.

The client can download (pull) file from server

or, the client can upload (push) file to server.

 FTP requires two connections between client and server:

The client establishes the 1st connection to the server on TCP port 21.

It consists of client commands and server replies.

The client establishes the 2nd connection to the server over TCP port 20.

This connection is for the actual file transfer and is created every time there is a
file transferred.

Dynamic Host Configuration Protocol (DHCP)

 The DHCP service enables devices on a network to obtain IP
addresses and other information from a DHCP server.

This service automates the assignment of IP addresses, subnet masks,
gateway and other IP networking parameters.

 When the DHCP server is contacted and an address requested.

The DHCP server chooses an address from a configured range of
addresses called a pool and assigns (“leases”) it to the host for a set
period.

If the host is powered down or taken off the network, the address is
returned to the pool for reuse.

This is especially helpful with mobile users that come and go on a network.

 Various types of devices can be DHCP servers when running DHCP
service software.

The DHCP server in most medium to large networks is usually a local dedicated
PC-based server.

With home networks, DHCP server is located at the ISP and a host on the home
network receives its IP configuration directly from the ISP.

 DHCP can pose a security risk because any device connected to the
network can receive an address.

This risk makes physical security an important factor when determining whether
to use dynamic or manual addressing.

 Dynamic and static addressing both have their places in network designs.

Many networks use both DHCP and static addressing.

DHCP is used for general purpose hosts such as end user devices,

Fixed addresses are used for network devices such as gateways, switches,
servers and printers.

Dynamic Host Configuration Protocol (DHCP)

DHCP
 When a DHCP-configured device boots up,

The client broadcasts a DHCP DISCOVER packet to identify any available
DHCP servers on the network.

A DHCP server replies with a DHCP OFFER, which is a lease offer message
with an IP address, subnet mask, DNS server, and default gateway.

The client may receive multiple DHCP OFFER packets if there is more than one
DHCP server on the local network, so it must choose between them, and
broadcast a DHCP REQUEST packet that identifies the explicit server.

Assuming that the IP address requested by the client, or offered by the server, is
still valid, the server would return a DHCP ACK message that acknowledges to
the client the lease is finalized.

DHCP
 When a DHCP-configured device boots up,

If the offer is no longer valid – perhaps due to a time-out or another client
allocating the lease – then the selected server will respond with a DHCP
NAK message (Negative Acknowledgement).

If a DHCP NAK message is returned, then the selection process must begin
again with a new DHCP DISCOVER message being transmitted.

 Once the client has the lease, it must be renewed prior to the lease expiration
through another DHCP REQUEST message

 The fourth CCNA Exploration course will cover the operation of DHCP in greater
detail.

File Sharing Services and SMB Protocol

 The Server Message Block (SMB) is a client/server file sharing protocol.

IBM developed SMB in the late 1980s to shared network resources, such as
directories, files, printers.

Is a request-response protocol: clients establish long term connection to servers

Once the connection is established, the user of the client can access the resources
on the server as if the resource is local to the client host.

 SMB file-sharing and print services have become the mainstay of Microsoft
networking.

Beginning with Windows 2000, all subsequent Microsoft products use DNS
naming. This allows TCP/IP protocols to directly support SMB resource sharing, as
shown in the figure.

 The LINUX and UNIX operating systems also provide a method of sharing
resources with Microsoft networks using a version of SMB called SAMBA.

 The Apple Macintosh operating systems also support resource sharing using
the SMB protocol.

File Sharing Services and SMB Protocol

 The SMB protocol describes file system access and how clients can make
requests for files.

 It also describes the SMB protocol inter-process communication.

 All SMB messages share a common format. This format uses a fixed-sized
header followed by a variable-sized parameter and data component.

 SMB messages can:

Start, authenticate, and terminate sessions

Control file and printer access

Allow an application to send or receive messages to or from another device

File Sharing Services and SMB Protocol

P2P Service and Gnutella Protocol
 With P2P applications based on the Gnutella protocol, people can make files on

their hard disks available to others for downloading.

pronounced /nʊˈtɛlə/ with a silent g,

Gnutella-compatible client software allows users to connect to Gnutella services over the
Internet and to locate and access resources shared by other Gnutella peers.

Many client applications are
available for accessing the
Gnutella network, including:
BearShare, Gnucleus,
LimeWire (screen capture
below), Morpheus, WinMX
and XoloX

http://en.wikipedia.org/wiki/Help:Pronunciation

P2P Service and Gnutella Protocol
 Many P2P applications do not use a central database to record all the files available

on the peers.

Instead, the devices on the network each tell the other what files are available when
queried and use the Gnutella protocol and services to support locating resources.

 When a user is connected to a Gnutella service, the client applications will search
for other Gnutella nodes to connect to.

These nodes handle queries for resource locations and replies to those requests.

They govern control messages,
which help service discover nodes

The actual file transfers usually
rely on HTTP services.

 The Gnutella protocol defines
five different packet types:

ping – for device discovery

pong – as a reply to a ping

query – for file location

query hit – as a reply to a query

push – as a download request

Telnet Service and Protocol

 Telnet provides a standard method of emulating text-based terminal
devices over the data network.

Both the protocol itself and the client software that implements the protocol are
commonly referred to as Telnet.

 A connection using Telnet is called a Virtual Terminal (VTY) session, or
connection.

To support Telnet client connections, the server runs a service (Telnet daemon)

A virtual terminal connection is established from an end device using a Telnet
client application.

Most operating systems include an Application layer Telnet client.

On a Microsoft Windows PC, Telnet can be run from the command prompt.

Other common terminal applications that run as Telnet clients are
HyperTerminal, Minicom, and TeraTerm.

 Telnet is a client/server protocol and it specifies how a VTY session is
established and terminated.

Each Telnet command consists of at least two bytes.

The first byte is a special character called the Interpret as Command (IAC) character.

The next byte as a command.

Some sample Telnet protocol commands include:

Are You There (AYT) – Lets the user request that something appear on the terminal
screen to indicate that the VTY session is active.

Erase Line (EL) – Deletes all text from the current line.

 The Telnet protocol supports user authentication, it does not support the
transport of encrypted data.

All data exchanged during a Telnet sessions is transported as plain text across
the network.

If security is a concern, the Secure Shell (SSH) protocol offers an alternate and
secure method for server access.

SSH provides stronger authentication than Telnet and supports the transport of
session data using encryption.

Telnet Service and Protocol

Telnet Service
and Protocol