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Semester
3 Chapter 1:
OSI
Model
Identify
and describe the functions of each of
the seven layers of the OSI reference
model.
Application:
This
layer provides services to application
processes, such as E-mail, file transfer
and terminal emulation, that are outside
the OSI reference model. The application
layer identifies and establishes the
availability of intended communication
partners (and the resources required to
connect with them), synchronises
cooperating applications, and
establishes agreement on provedures for
error recovery and control of data
integrity.
Presentation:
This
layer ensures that information sent by
the application layer of one system will
be readable by the application layer of
another. The presentation layer is also
concerned with the data structures used
by programs amd therefore negotiates
data transfer syntax for the application
layer.
Session:
The
session layer establishes, manages and
terminates sessions between applications
and manages data exchange between
presentation layer entities.
Transport:
This
layer is responsible for reliable
network communication between end nodes.
The transport layer provides mechanisms
for establishment, maintenance and
termination of virtual circuits,
transport fault detection and recovery,
and information flow control.
Network:
The
network layer provides connectivity and
path selection between two end systems.
The network layer is the layer at which
routing occurs.
Data
Link:
Provides
transit of data across a physical link.
The data link layer is concerned with
physical addressing, network topology,
line discipline, error notification,
oredered delivery of frames and flow
control. The IEEE divides the layer into
two sub layers: the MAC sublayer and the
LLC sublayer.
Physical:
The
physical layer defines the electrical,
mechanical, procedural, and functional
specifications for the physical links
between systems.
Define
and explain the 5 conversion steps of
data encapsulation.
1:
Build the data: As a user sends for
example, an email message, its
alphanumeric characters are converted to
data that can travel across the
internetwork.
2:
Package the data for end to end
transport: The data is packaged for
internetwork transport. By using
segments, the transport function ensures
that the message hosts at both ends of
the email system can reliably
communicate.
3:
Add the network address to the header:
The data is put into a packet or a
datagram that contains a network header
with source and destination logical IP
addresses. These network addresses help
network devices send the packets across
the network along a dyna,ically chosen
path.
4:
Add the local (MAC) address to the data
link header: Each network device must
put the packet into a frame. The frame
includes a header with the physical
address of the next directly connected
device in the path.
5:
Convert to bits for transmission: The
frame must be converted into a pattern
of 1s and 0s (bits) for transmission on
the medium (usually a wire). A clocking
function enables the devices to
distinguish these bits as they travel
across the medium. The medium on the
physical internetwork can vary along the
path used.
Identify
at least 3 reasons why the industry uses
a layered model.
-
It breaks the network into
smaller, simpler parts that are easier
to develop
-
It facilitates standardisation of
network components to allow multiple
vendor development and support.
-
It allows different types of
network hardware and software to
communicate with each other.
-
Prevents changes in one layer
from affecting the other layers, so that
they can develop more quickly.
Addressing
Define
and describe the function of a MAC
address.
A
standardised data link layer address
that is required for every device that
connects to a LAN. Other devices in the
network use these addresses to locate
specific devices in the network and to
create and update routing tables and
data structures. MAC addresses are six
bytes long and are controlled by the
IEEE.
A
MAC address is a 48-bit address
expressed as 12 hexadecimal digits. The
first six hexadecimal digits of a MAC
address contain a manufacturer
identification, also known as an
Organisationally Unique Identifier. The
last six hexadecimal digits are
administered by each vendor and often
represent the interface serial number.
Describe
data link addresses and network
addresses, and identify the key
differences between them.
Data
link addresses are addresses that reside
at the data link layer of the OSI model.
Data link addresses are MAC addresses.
MAC addresses are flat addresses, that
is, they have no hierarchy, unlike
network addresses. Network addresses are
made up of two main parts; a network
portion and a host portion. The network
portion identifies the network that the
host resides on. Routers use network
layer addresses to make path
determination decisions for network
layer packets. Routers also use the data
link layer address to send the packet to
its intended destination host. As a
packet trvels across a network, the IP
address of the destination never changes
but the data link address changes so
that the packet can be switched to the
next hop.
Describe
and create the different classes of IP
addresses [and subnetting].
Class
A addresses use the first 8 bits of the
IP address to identify the network which
the host belongs to. A class A IP
address is in the range 0.0.0.0 to
127.255.255.255, although the 127.0.0.0
address range is reserved for special
purposes. The subnet mask of 255.0.0.0
will also identify a class A network.
Also, the first bit in a class A address
is always 0.
Class
B IP addresses have the first two bits
of their addresses set to 10. This puts
class B IP in the range 128.0.0.0 to
191.255.255.255. Class B networks always
use the first 16 bits of the IP address
to identify the network. Class B
networks always have the subnet mask
255.255.0.0.
Class
C networks are identified by having the
first three bits of their IP addresses
set to 110. The range for class C IP
addresses is 192.0.0.0 to
223.255.255.255.
Subnetting
involves borrowing contiguous bits from
the host range in an IP address. To
subnet you must borrow at least two bits
and leave two bits. You cannot have all
0s or 1s for a subnet ID. Therefore the
number of usable subnets is always 2
less than the total. To work out how
many subnets you have created you should
multiply 2 to the power of the number of
bits you have borrowed. EG. 2^2 = 4, 2^3
= 8, 2^4 = 16. For every contiguous bit
you borrow from a host range, you double
the amount of subnets possible.
Identify
the functions of the TCP/IP Transport
Layer Protocols.
The
TCP/IP Transport layer provides two
protocols, Transmission Control Protocol
and User Datagram Protocol.
TCP
is a connection oriented reliable
protocol that provides flow control by
providing sliding windows and offers
reliability by providing sequence
numbers and acknowledgements. TCP
resends anything that is not
acknowledged and supplies a virtual
circuit between end user applications.
The advantage of TCP is that it provides
guaranteed delivery of segments.
UDP
is a connectionless unreliable protocol
that is responsible for transmitting
messages but provides no software
checking for segment delivery. The
advantage of UDP is speed. Because UDP
provides no acknowledgements, less
traffic is sent across the network,
making transfer faster.
IOS
Log
into a router using both user and
priviledged modes.
Router
con0 is now available
Press
Return to get started
User
access verification
Password:
Router>
Router>enable
Password:
Router#
Use
the context-sensitive help facility
Typing
a question mark (?) at the user mode
prompt (Router>) or privileged prompt
(Router#) will display a list of context
sensitive, commonly used commands
Use
the command history and editing
features.
Ctrl-P
or Up arrow key: Recalls last (previous)
command
Ctrl-N
or Down arrow key: Recalls most recent
command
Show
History: Shows command buffer
Ctrl-A:
Moves to the beginning of the command
line
Ctrl-E:
Moves to the end of the command line
Esc-B:
Moves back one word
Ctrl-F:
Moves forward one character
Ctrl-B:
Moves back one character
Esc-F:
Moves forward one word
Examine
router elements (RAM, ROM, CDP, show)
RAM:
Stores routing tables, the ARP cache,
the fast-switching cache, packet
bufferring and packet hold queues. RAM
also provides running memory for the
routers configuration file while the
router is powered on.
ROM:
Contains power-on diagnostics, a
boot-strap program, and operating system
software. Software upgrades in ROM
require replacing pluggable chips on the
motherboard.
CDP:
The Cisco discovery protocol provides a
single proprietary command that enables
network administrators to access a
summary of what the configurations look
like on other directly connected routers
Show:
show <command> helps you obtain
vital information that you need when
monitoring and troubleshooting router
operations.
Manage
configuration files from the priviledged
exec mode.
configure
terminal: Configures the router manually
from the console terminal
configure
memory: Loads configuration information
from non-volatile random access memory.
copy
tftp running-config: Loads configuration
information from a network tftp server
show
running-config: Displays the current
configuration in RAM
copy
running-config startup-config: Stores
the current configuration in RAM into
NVRAM
copy
running-config tftp: Stores the current
configuration in RAM on a network tftp
server
show
startup-config: Displays the saved
configuration, which is the contents of
NVRAM
erase
startup-config: Erases the contents of
NVRAM
Control
router passwords, identification, and
banner.
Router
Passwords:
enable
password <password>
enable
secret <password>
Identification:
hostname
<Router Name>
Banner:
banner
motd# <Type your message here>
Identify
the main Cisco IOS commands for router
startup.
Router#
show running-config
Router#
show startup-config
Router#
copy running-config startup-config
Router#
reload
Enter
an initial configuration using the setup
command.
Router#
setup
Enter
Hostname:
Enter
Enable Secret:
Enter
Enable Password:
Enter
Virtual Terminal Password:
Configure
IP? [Yes]
Configure
Interface Serial0: Yes
Configure
Interface Serial1: Yes
Configure
Interface Ethernet 0: Yes
Configure
Interface Ethernet 1: Yes
Copy
and manipulate configuration files.
configure
terminal: Configures the router manually
from the console terminal
configure
memory: Loads configuration information
from non-volatile random access memory.
copy
tftp running-config: Loads configuration
information from a network tftp server
show
running-config: Displays the current
configuration in RAM
copy
running-config startup-config: Stores
the current configuration in RAM into
NVRAM
copy
running-config tftp: Stores the current
configuration in RAM on a network tftp
server
show
startup-config: Displays the saved
configuration, which is the contents of
NVRAM
erase
startup-config: Erases the contents of
NVRAM
List
the commands to load Cisco IOS software
from: flash memory, a TFTP server, or
ROM.
Router
(config)# boot system flash IOS_filename
Router
(config)# boot system tftp IOS_filename
tftp_address
Router
(config)# boot system rom
Prepare
to backup, upgrade, and load a backup
Cisco IOS software image.
show
flash
copy
flash tftp
copy
tftp flash
Prepare
the initial configuration of your router
and enable IP.
Router>ena
Password:
Router#configure
terminal
Router(config)#hostname
<name>
Hostname(config)interface
e0
Hostname(config-if)ip
address <address> <subnet
mask>
Hostname(config-if)no
shut
Add
the RIP routing protocol to your
configuration.
Hostname(config-if)router
rip
Hostname(config-router)network
xxx.xxx.xxx.xxx
Configure
IP Addresses.
Hostname(config)interface
e0
Hostname(config-if)ip
address <address> <subnet
mask>
Hostname(config-if)no
shut
Verify
IP Addresses.
ping
<ipaddress>
show
interface e0/1/2/3 s0/1/2/3
show
ip interface
Explain
the services of separate and integrated
multiprotocol routing.
Routers
are capable of concurrently supporting
multiple independant routing protocols
and maintaining routing tables for
several routed protocols.
List
problems that each routing type
encounters when dealing with topology
changes and describe techniques to
reduce the number of these problems.
Static
Routing:
Static
routing is where the network
administrator has to input route changes
directly into the routing table whenever
there is a change to the networks
topology. One way to solve the problem
of constantly having to manually update
routing tables is to employ a dynamic
routing protocol. Dynamic routing
protocols automatically adjust routing
tables whenever there is a change to the
topology by passing periodic or event
triggered updates to neighbouring
routers. These neighbouring routers then
update their routing tables and
recalculate the best routes to known
networks.
Dynamic
Routing:
Dynamic
Routing protocols encounter the problem
of routing loops. Routing loops occur
when routers suffer from slow
convergence due to differing line speeds
and latency. Because routers do not have
a consistent view of the network,
routing updates can activate routes that
a previous router has stated is
unreachable. This can cause a count to
infinity where the routers' metric
counts to infinity as the packets loop
around and around. The distance vector
protocol answer to the count to infinity
problem is to define a maximum. Distance
vector protocols have a maximum hop
count. When the packet has the maximum
hop count value, the router discards the
packet.
Another
answer to the problem of routing loops
is the Split Horizon. Split Horizon
stops a router that received an update
sending the same information out of the
the same interface.
Holddown
timers are also used to prevent routing
loops. Holddown is when a router will
reject routing updates with a poorer
metric than it originally received from
a neighbour router that indicates the
network is down. If the router receives
an update from that same router it will
mark the route as accessible. If the
router receives an update from another
router with a poorer metric for the same
route, it rejects the update for the
holddown period.
A
poison reverse update is designed to
prevent larger routing loops. A poison
reverse updates explicitly indicate that
a network or subnet is unreachable,
rather than implying that a netwrok is
unreachable by excluding it in updates.
Chapter 2:
LAN
Switching
Describe
the advantages of LAN segmentation.
The
primary reason to segment LANs is to
isolate traffic between segments and to
achieve more bandwidth per user by
creating smaller collision domains. Each
segment is its own collision domain.
Without LAN segmentation, LANs larger
than a small workgroup would quickly
become clogged with traffic and
collisions and would deliver severely
reduced bandwidth.
Describe
LAN segmentation using bridges.
Bridges
learn a network's segmentation by
building address tables that contain the
physical address of each networkdevice,
as well as the port to use to reach the
device. Ethernet bridges are transparent
to the other devices on the network
Describe
LAN segmentation using routers.
A
router operates at the network layer and
bases all of its forwarding decisions on
the layer 3 protocol address. It
accomplishes this by examining the
destination address on the data packet
and then looking in its routing table
for forwarding intstructions.
Describe
LAN segmentation using switches.
A
LAN switch is a high-speed multi-port
bridge that has one port for each node
or segment of the LAN. A switch segments
a LAN into microsegments, thereby
creating collision-free domains from one
formerly larger collision domain.
Switches make frame forwarding decisions
by building a table of the MAC addresses
of the hosts attached to each port.
Describe
the benefits of network segmentation
with bridges.
Ethernet
LANs that use a bridge for segmenting
the LAN provide more bandwidth per user
because there are fewer users on the
segments than when compared to the
entire LAN. The bridge only allows those
frames that have destinations outside
the segment to pass through.
Describe
the benefits of network segmentation
with routers.
Routers
create the highest level of segmentation
because of their capability to make
exact determinations of where to send
the data packet.
Describe
the benefits of network segmentation
with switches.
In
switched ethernet, each node is directly
connected to one of its ports or a
segment that is connected to one of the
switch's ports. This creates a 10/100
Mbps connection between each node and
each segment on the switch. A computer
directly connected to an ethernet switch
is its own collision domain and accesses
the full 10/100 Mbps.
Name
and describe two switching methods.
Store
And Forward:
The entire frame is received before any
forwarding takes place. The destination
and/or the source address are read and
filters are applied before the frame is
forwarded.
Cut-Through:
The switch reads the destination address
before receiving the entire frame. The
frame is then forwarded before the
entire frame arrives.
Fast-forward
switching:
This method of switching offers the
lowest level of latency by immediately
forwarding a packet after receiving the
destination address. Because
fast-forward switching does not check
for errors, there may be times when
frames are relayed with errors. Although
this occurs infrequently and the
destination network adapter discards the
faulty frame upon receipt.
Fragment-free
switching: Fragment-free
switching filters out collision
fragments, which are the majority of
packet errors, before forwarding begins.
Fragment-free switching waits until the
received packet has been determined not
to be a collision fragment before
forwarding the packet
Distinguish
between cut-through and
store-and-forward switching.
Cut-through
- The switch reads the destination
address before receiving the entire
frame. The frame is then forwarded
before the entire frame arrives. This
mode decreases the latency of the
transmission and has poor LAN Switching
error detection.
Fast-forward
switching -
This method of switching offers the
lowest level of latency by immediately
forwarding a packet after receiving the
destination address. Because
fast-forward switching does not check
for errors, there may be times when
frames are relayed with errors.
Fragment-free
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