Download Ethernet - Faculty - Genesee Community College

Chapter 9- Ethernet
Modified by Profs. Chen and Cappellino
Objectives

Learning Objectives

Upon completion of this chapter, you will be able
to:
 Describe the evolution of Ethernet
 Explain the fields of the Ethernet Frame
 Describe the function and characteristics of the
media access control method used by Ethernet
protocol
 Describe the Physical and Data Link layer
features of Ethernet
 Compare and contrast Ethernet hubs and
switches
 Explain the Address Resolution Protocol (ARP)
Historic Ethernet - FYI

The foundation for Ethernet technology was first
established in 1970 with a program called Alohanet.
Alohanet
was a digital radio network designed to transmit
information over a shared radio frequency between the Hawaiian
Islands.
Alohanet required all stations to follow a protocol in which an
unacknowledged transmission required re-transmitting after a short
period of waiting.

The techniques for using a shared medium in this way
were later applied to wired technology in the form of
Ethernet.
Ethernet
was designed to accommodate multiple computers that
were Interconnected on a ________________________

The first version of Ethernet incorporated a media access
method known as Carrier Sense Multiple Access with
Collision Detection (_______________).
Ethernet – Standard and Implementation



Ethernet operates in the __________
_____________ of the OSI model:
the __________________________
(L2) and the _________________ (L1).
The first Ethernet standard was
published in 1980 by a consortium of
Digital Equipment Corporation, Intel,
and Xerox (DIX).
In 1985, the Institute of Electrical and
Electronics Engineers (IEEE) standards
committee published standards for
LANs.
These
standards start with the number 802.
The ______________________________
Ethernet – Layer 1 and Layer 2

The Physical layer
 Review:
Ethernet at Layer 1 involves signals, bit
streams, physical components that put signals on
media, and various topologies.

Ethernet is actually implemented in the
_______________ of the Data Link
layer, which is known as the _________
_____________________________
 Ethernet
at Layer 2 addresses the limitations that
exist in layer 1– see chart…
 The MAC sublayer is concerned with the ______
________________________________________
______________________________ and
__________________________ over the media.

The ____________________ sublayer
of the Data Link layer remains relatively
___________ of the physical equipment
 Acts
as an ______________________________
____________________________________
Logical Link Control Sublayer of the Data Link Layer
IEEE 802.2 standard describes the LLC
sublayer
 LLC handles the _____________ between
the ______________ and the hardware of
the MAC sublayer and _____________
 LLC is implemented ___________ and
takes the network protocol data (L3), and
______________________ to help deliver
the packet to the destination node.
 _________________________________

MAC Sublayer of the Data Link Layer



IEEE _______ standard describes the MAC sublayer and
the Physical layer functions.
MAC is implemented in hardware, typically in __________
MAC sublayer has _________ responsibilities:
1. ______________ including frame assembly prior to
transmission and frame parsing when frame is received

Frame __________________________________ that make up
a frame



Each __________________________________________ that
enables a frame to be delivered to a destination node.


The MAC layer _____________________ to the Layer 3 PDU.
It __________________________ between the transmitting and
receiving nodes.
More to come on MAC addresses…
________________________

Each trailer contains a ________________. If the CRC of the
_________________________________, the frame can be
______________ to have been received without error.
MAC Sublayer responsibilities
cont…
2. Media Access Control
 The
____ sublayer controls the _________
__________________________________
___________________________

Includes recovery from transmission failure due to
collisions.
 The
media access control method for
Ethernet is _________________
All the nodes in that network segment ________
_________________________________
 ___________________________________________
transmitted by any node on that segment.
 They examine the MAC address to determine if
frame is meant for themselves

Physical Implementations of Ethernet

Ethernet has evolved to meet the increased
demand for high-speed LANs due to the
introduction of fiber optics.
Ethernet
is simple, easy to maintain and upgrade,
reliable and cost effective



With the introduction of Gigabit speeds, Ethernet
has become a Metropolitan Area Network (MAN)
and WAN standard.
Ethernet can _____________________________
______________________________
Ethernet supports a variety of media types but the
_______________________________________
_____________________________
Uses
different media to interconnect network devices
via intermediary devices such as hubs and switches.
Early Ethernet Media- Bus topology

The first versions of Ethernet used
________ to connect computers in
a physical bus topology.
Each
_____________________
______________________
This versions of Ethernet were known
as _____________, (10BASE5) and
_______________ (10BASE2).



__________, used a _____________________
_____________________ before the signal
required a repeater.
_______________, used a ______________
______________________________________
________________________________
Coaxial cables where eventually
replaced with UTP cables
UTP
was easier to work with,
lightweight, and less expensive
Early Ethernet Media- Star topology

Physical topology eventually changed to a
____________________________
 _________

concentrate connections
When a frame arrives at one port, it is __________
_____________________________________
 Hubs
_______________________ by allowing
any single cable to fail without disrupting the
entire network.
Ethernet Collision Management

Legacy Ethernet (Hub and half-duplex)
10BASE-T
networks used hubs as the central point of the network
segment
______________enabled only ________________________
______________________________________
As ___________ were added to an Ethernet network, the amount
of frame ________________ significantly.

Current Ethernet (switch and full-duplex)
– around development of 100BASE-TX- were
introduced to __________________________________
____________

isolate each port and _______________________________ (if the
destination is known), rather than send frame to every device.
Later


______________________________ was introduced
connections that ________________________________________
at the ___________________________
In full duplex mode, there is no contention for the media. Thus, a
_____________________________________
The Frame




– Encapsulating the Packet
Review of Frame from Chapter 7-The Ethernet frame structure adds headers and
trailers around the Layer 3 PDU.
There are 2 Ethernet framing- what are they?
Ethernet Frame Size
Both
Ethernet standards define the minimum frame size
as 64 bytes and the maximum as 1522 bytes (extended
from 1518 bytes)

This includes all bytes from the Destination MAC Address field
through the Frame Check Sequence (FCS) field.


The Preamble and Start Frame Delimiter fields are not included
The frame size was increased to accommodate a technology
called Virtual Local Area Network (VLAN).
____________________________________________
___ _______________________________________
Review- what field is it?
The Ethernet MAC Address
in more detail…
A unique identifier called a Media Access Control (______)
__________ was created to _________________
_____________________________________
It
provided a method for device identification at a lower level of the
OSI model.


REVIEW…
What layer does the MAC address belong to?
What is the size of the MAC address?
 What is another name
for a MAC address?
MAC Address Structure

Any vendor that sells Ethernet devices must
register with IEEE who will assign a 3-byte
Organizational Unique Identifier (____) to that
vendor
 A ________________________________

Requirements:
 All
MAC addresses assigned to a NIC must use
that ______________________________
_____________________________
 All MAC addresses with the same OUI must be
assigned a unique value in the last 3 bytes.

The MAC address is often referred to as a
burned-in address (____) because it is
___________________________________
 When
the computer starts up, the NIC copies
the address into RAM.
 The address is used to compare with the
destination address of a received frame.
Ensures unique MAC
address gets assigned
to all devices
How a MAC is used on a LAN

When a device forwards a message in an
Ethernet network, each NIC in the (local)
network sees if the destination MAC address
matches its address.
 If
 If
there is ___________________________________
there is a _________, that device’s ___________
______________, where the _______________
process take place.

All devices connected to an Ethernet LAN have
MAC addressed interfaces including
workstations, servers, switches, printers etc.
Hexadecimal (“Hex”) Numbering and Addressing


_____________ is used to ______________________
addresses and IP Version 6 addresses.
Hexadecimal is a base ______________ system.
 It uses the ________________________________
 Hex is a way to represent binary values



Each Hex digit is up to ____________________
Review: what base is decimal? And binary?
Given that 8 bits (a byte) is a common binary grouping,
 Binary
00000000 to 11111111 can be represented in
hexadecimal as the range _________________
 Leading zeroes are always displayed to complete the 8-bit
representation
 Given the chart at the right- what is the Hex equivalent of the
following: 0010 1011


Hexadecimal is usually ________________________
_______________________________ (for example 0x73)
to distinguish it from a decimal value.
NOTE: you should be able to convert Hex to binary to
decimal or vice-versa
 Review:
1011?
How would be calculate the DECIMAL VALUE OF
Addressing Review…

Data Link layer (Layer 2) physical
addressing, implemented as an
Ethernet MAC address, is used to
transport the ________________
_________________________
These
addresses have _______________
___________________________
Source and Destination MAC addresses
_________________________________

Network layer (Layer 3) addresses,
such as ______________, provide
________________ that is understood
at both source and destination and
_________________________
Source
and Destination ____________
______________ at all from start to finish
The Network layer address enables the
packet to be forwarded toward its
destination.
Ethernet Unicast, Broadcast & Multicast


A _______ MAC address is the
___________ used when a frame
is sent from a ______________
__________________________
______________ device.
In the example shown, a host
with IP address 192.168.1.5
(source) requests a web page
from the server at IP address
192.168.1.200.
The
destination IP address and MAC
address combine to deliver data to
one specific destination host.
Notice- both source and destination
are on the same network

HOW DO WE KNOW THAT?
Ethernet Unicast, Broadcast & Multicast

With a _______________________
_______________________________
____________________________
Direct broadcast
 This numbering in the address means that ____
_______________________________________
_____________________________________


Network protocols, such as Dynamic
Host Configuration Protocol (______)
and Address Resolution Protocol
(_____), __________________
On Ethernet networks, the broadcast
MAC address on the frame is 48
binary ones displayed as Hexadecimal
___________________________
Ethernet Unicast, Broadcast & Multicast

___________ addresses allow a ________
__________________________________.
 Devices
that belong to a multicast group are
assigned a _____________________ ranging
from ______________________________
 ___________ used as the ___________ of a
packet while the ___________ will always
have a _______________________

Multicast IP address requires a corresponding
multicast MAC address to actually deliver
frames on a local network.
 The
_____________________________
________________________ in hexadecimal.
 The value ___________________________
_____________________________________
__________________ of the multicast MAC
address.
 The leading bit in the last half of the MAC
address is always a binary "0".
Media Access Control in Ethernet- Review

In a shared media environment, all devices
have guaranteed access to the medium
If
more than one device transmits
simultaneously, what happens?

Ethernet uses Carrier Sense Multiple Access
with Collision Detection (CSMA/CD) to
detect and handle collisions and manage the
restart of communications.
CSMA/CD – The Process

Carrier Sense
 ____________________________________________
for electrical
activity on the cable before transmitting.
 If a device _________________ from another device, it will _________ for
a specified amount of time before attempting to transmit.
 When there is ____________, a device ________________ its message.
 While this transmission is occurring, the __________________________
for traffic or collisions on the LAN.
 After the message is sent, the ______________________________

Multi-access
 If
the distance between devices is such that the one device's signals are
not detected by a second device, ____________________________
__________________________________- Their messages will propagate across the media until they
_____________________________________
 At that point, the _________________________________________
 Although the messages are corrupted, the jumble of remaining signals
_______________________ across the media.
CSMA/CD – The Process cont…

Collision Detection
Once
a collision occurs, the ______________________ - as well
as all the transmitting devices - _______________________
__________________________ above the normal level
Once detected, every device transmitting will continue to transmit
to _________________________________________________

Jam Signal and Random Backoff
Once
the collision is detected by the transmitting devices, they
_____________________ used to notify the other devices of a
collision, so that they will __________________________

This backoff algorithm causes all devices to __________________
_________________, which allows the collision signals to subside.
A __________________
ensures that the devices that were
involved in the collision do not try to send their traffic again at the
same time, which would cause the whole process to repeat.
Hubs and Collision Domains


Collisions will occur in many shared media topologies
______ were created as intermediary network devices that
enable ______________________________________
Because
hubs operate at the ___________________, _________
____________________ between the devices they connect.
Hubs retransmit ____________________________________,
except the one from which it received the signal

_______________________________________________
____________________________ or series of directly
connected hubs (see next slide for graphic of a collision domain)
A collision
domain can also be considered a _________________.
Hubs _________________ of the collision domain.

Seen on the next slide, the interconnection of hubs form a
physical topology called an extended star and _________
_______________________
Hubs and Collision Domains Graphic
Need
something
more than
CSMA/CD to
control
collisions in a
large
networked
environment
Stay tuned…
Collision domains

The types of devices that interconnect the media
segments define collision domains.
___________________________________________

Examples of Layer 1 devices: repeaters and hubs

_________________ the collision domains
____________________________________________
______________________________
 Breaking up, or ___________________________
______________ with Layer 2 and 3 devices is also
known as segmentation
 Layer 2 device- _____________
 Layer 3 device- _____________
Segmentation with switch
How many
collision domains
do we have?
Segmentation with router
How many
collision
domains do
we have
here?
Ethernet Timing: Latency

When a device wants to send a message,
the electrical ______________________
______________________ called _______
to travel down the cable.
Each
hub adds latency as it forwards the bits
from one port to the next.

The ___________________________
increases the likelihood that ___________
will occur
Listening
node may begin transmitting signals
while the hub is processing the message.
Ethernet Timing: Timing and Synchronization

_________ 64 bits of __________________
information
Transmitted


by the sending device in half-duplex mode
The sending device ______________________
__________________________________
Ethernet with throughput speeds of __________
________ are ____________________.
Meaning
each ____________________________
___________________________________

Ethernet implementations with throughput of
____________________ are _______________.
Synchronous
communication in this context means
that the _________________________________
Ethernet Timing: Bit Time

___________ For each
different media speed this is
the __________________
_______________________
______________________
For
100 meters of UTP cable,
it takes just under 5 bit times
for a 10BASE-T signal to
travel the length the cable.
Ethernet Timing: Slot Time

__________ time it takes for an __________
_____________________________________
____________________________________
Slot
time is calculated assuming maximum cable
lengths on the largest legal network architecture


In half-duplex Ethernet, slot time becomes an
important parameter in determining how many
devices can share a network.
The _________________________________
_____________________________________
_______________________ (4096 for Gigabit
Ethernet) of the frame transmission.
Interframe Spacing

Ethernet standards require a
minimum spacing between two
non-colliding frames.
Gives
the media time to stabilize
after the transmission of the
previous frame and time for the
devices to process the frame.

_________________ is the ____
measured from the _________
__________________________
__________________________
_____________________
Jam Signal

As soon as a collision is detected, the
sending devices transmit a 32-bit "jam"
signal that will enforce the collision and
ensure all devices in the LAN to detect
the collision.
It
is important that the ________________
___________________________________;
otherwise the collision would not be
identified.

The corrupted, __________________
______________ are often referred to as
collision fragments or ____________.
Backoff Timing

After a collision occurs and all devices allow the
cable to become idle (each waits the full
interframe spacing), the devices must ________
__________________________________
before attempting to retransmit
Randomization
is important so that two stations do not
transmit at the same time, which would result in more
collisions.

The methods described in this section allowed
Ethernet to provide greater service in a shared
media topology based on the use of hubs.
With
the use of switches, the need for CSMA/CD
starts to diminish or, in some cases, is removed
altogether– stay tuned…
Overview of Ethernet Physical Layer


The ____________ between standard
Ethernet, Fast Ethernet, Gigabit
Ethernet, and 10 Gigabit Ethernet
__________________________
Ethernet is covered by the IEEE
802.3 standards. Four data rates are
currently defined for operation over
optical fiber and twisted-pair cables:
______
Mbps - ___________ Ethernet
____ Mbps - _________ Ethernet
______ Mbps - _________ Ethernet
10 Gbps - 10 Gigabit Ethernet

There are many different
implementations of Ethernet at these
various data rates
10 Mbps Ethernet

The principal 10 Mbps implementations of Ethernet
include:
10BASE5 using Thicknet coaxial cable (bus topology)
10BASE2 using Thinnet coaxial cable (bus topology)
10BASE-T using Cat3-Cat5 unshielded twisted-pair cable
topology)

(star
10 Mbps Ethernet - ________________
______________________ is typically used today
10BASE-T uses ___________________ and is ___________
each end with an 8-pin _____________________

It
It
at
It uses Manchester-encoding over two unshielded twisted-pair cables.
uses a _______________________
could be up to __________________________________ (or
repeater)
The
10BASE-T links connected to a switch can support either halfduplex or full-duplex operation.
100 Mbps Fast Ethernet

100 Mbps AKA Fast Ethernet
Can
be _____________________________________________.
Higher frequency signals make Fast Ethernet _______________
__________________
Two main types…

100BASE-TX (Cat5 or later UTP)
 Designed
to support _____________________________________ copper
wire or ________________________
 Uses 4B/5B encoding
 Is ______________________________________________ at the center

100BASE-FX (fiber-optic cable)
 100BASE-FX
standard uses the same signaling procedure as 100BASETX, but ___________________________ rather than UTP copper.
 Encoding, decoding, and clock recovery procedures are the same for both
media,
 Signal transmission is different - ___________________________
 100BASE-FX uses the duplex SC connector
1000 Mbps Ethernet

1000 Mbps AKA Gigabit Ethernet
 Can
be _____________________________
________________________________
 With signals occurring in less time, bits
become even _________________________
than Fast Ethernet

______________________
 Two
main types
More to come…
1000Base-T Ethernet
 1000Base-SX and 1000Base-LX using Fiber

1000BASE-T Ethernet

Provides ______________________________
____________________________________
Gigabit
Ethernet over copper wire enables 125 Mbps
per wire pair, or ____________________________
Each wire pair signals in full duplex, doubling the 500
Mbps to _____________________



Can ______________________________________________
____________________________
Uses 4D-PAM5 line encoding to obtain 1 Gbps
data throughput.
Unlike most digital signals where there are usually
a couple of discrete voltage levels,
1000BASE-T
uses many voltage levels.
Looks similar to an analog signal rather than digital
1000BASE-SX and 1000BASE-LX

These ________________ of _______________
offer the following advantages over UTP:

small





physical size
Support full-duplex binary transmission at 1250
Mbps over two strands of optical fiber.
The transmission coding is based on the 8B/10B
encoding scheme.
The principal ________________- among the
1000BASE-SX and 1000BASE-LX fiber versions
are the ________________ and wavelength of
the optical signal
Ethernet - Future Options

The IEEE 802.3ae standard was adapted to include 10
Gbps, full-duplex transmission over fiber-optic cable.
10-Gigabit
Ethernet (10GbE) is evolving for use not only in LANs,
but also for use in WANs and MANs.

10Gbps can be compared to other varieties of Ethernet in
these ways:
______________________,
allowing _______________ between
all varieties of legacy, fast, gigabit, and 10 gigabit Ethernet.
Because only full-duplex fiber connections are used, CSMA/CD is
not necessary.
The IEEE 802.3 sublayers within OSI Layers 1 and 2 are
mostly preserved, with a few additions to accommodate 40 km
fiber links and interoperability with other fiber technologies.

Future Ethernet Speeds
The
IEEE and the 10-Gigabit Ethernet Alliance are working on 40, 100-, or even 160-Gbps standards.
Legacy Ethernet – Using Hubs

Classic Ethernet uses hubs to interconnect nodes
on the LAN segment.
 Hubs
___________________________________
 Forwards all the bits to every device connected to
the hub.
 ____________________________________
 May result in high levels of collisions on the LAN.

Sharing media creates issues as the network
grows.
 Scalability -with each device added to the shared
media, the _________________________________
____________________
 Latency
 __________________________________________
connected to a segment results in increased latency.
 The greater the latency the _________________
_______________________
 Network Failure- if any device connected to the hub
____________________, the _________________
on the media ___________________________.
 _________ a network with a larger number of nodes
contains more traffic and has a larger collision domain
Ethernet – Using Switches


A _____________________ network device
which _________________________________
____________________________
Looks like a hub
 Essential
distinction between hubs and switches is
that a ___________________________________
between hosts on a network.
Ethernet – Using Switches

Switches allow the ___________
______________________________
________________________
___________
of the switch represents a
____________________________
__________________ to the node or
nodes connected on that port.


With fewer nodes in each collision
domain, there is an ____________
______________________ to each
node, and ____________________.
In a LAN where a hub is connected to
a switch port, there is still shared
bandwidth, which may result in
collisions within the shared
environment of the hub.
Switch
will isolate the segment and help
reduce collisions
Using Switcheswith _____________________

_____________ of the network
___________ dramatically due to…
__________________________

Each device has a dedicated point-to-point
connection between the device and the switch,
without media contention.
____________________________


Each node is it’s own collision domain
If running NIC with _____________________
____________________________
Full-duplex


operation
With full-duplex enabled in a switched Ethernet
network, the devices connected directly to the
switch ports can transmit and receive
simultaneously, at the full media bandwidth.
Doubles transmission rates when compared to
half-duplex. How?
Ethernet – Why are hubs still being used?

______________
Early
Ethernet networks used hubs and many
of them remain in operation to this day.

____________________
As
the price of switches has dropped, the use
of hubs has decreased and cost is becoming
less of a factor in deployment decisions.

_____________________
In
certain (very few) LANs, shared media
hubs still suffice so are still used
Switches – Selective Forwarding

_________________________
_______________________________________
between
__________________________________
At this time, __________________ between them

Switches forward individual frames directly from the receiving
port to the destination port (if known) using selective forwarding
Switch
______________________________________
The _____________________________________. that matches a
destination MAC address with the port used to connect to a node.
For each incoming frame, the ______________________ in the frame
header is _______________________________ in the MAC table.


If a match is found, the ____________________ that is paired with the MAC
address is used as the ___________________________
The MAC table AKA the _______________ or the bridge table
or the __________________
Bridging- FYI

Bridges were devices used in early LANs
to connect two physical network
segments.
 Today-
______________________________
________________________

Today, bridges are used in wireless
networks to connect two wireless network
segments
Stay tuned to the next course…
Switches – Store and Forward


In __________________________, the switch
_______________________, checks the FSC for
errors, and ______________________________
______________ for the destination node.
Any node operating in full-duplex mode can
transmit anytime it has a frame, without regard to
the availability of the receiving node.
This
is because a LAN _________________________
___________________ and _____________________
__________ when that port is idle.

As a result of the ability to ___________ and
_______________________, _______________
________________________________
They
can send and receive at full media speed without
losses due to collisions or the overhead associated with
managing collisions.
Switch Operation
Ethernet LAN switches use ____basic operations:
1. __________________

This
process ________________________________
with MAC addresses and their corresponding ports
______________ during normal operation
As each frame enters the switch, the switch examines
the ______________ MAC address.

If ___________________________________________________ using
the _____________ MAC address and pairs the address with the
_________________________________________
The
switch now can use this mapping to forward frames
to this node.
2. _____________________
The entries in the MAC table are ________________
 After entry made in MAC table, a __________________ begins.
 When the value reaches 0, the entry in the table will be removed.
Switch Operation
3. ____________________
If
the ______________________ to which port to send a frame because
the destination MAC address is not in the MAC table, the switch
______________________________________________________
Flooding is also used for frames sent to the ______________________.
4. __________________________
Selective
forwarding is the process of ______________ a frame's
_____________ MAC address and _____________________________

The destination MAC address has already been learned and the
corresponding port added to the MAC table
Core
function of a switch
5. _______________ when a frame is __________ forwarded
A switch
does _________________________________________
A switch will _____________________________.

An

If a frame fails a CRC check
additional reason for filtering a frame is ____________________.
A switch has security settings for _______________________ to and/or from
selective MAC addresses.
The ARP Process – Mapping IP to MAC Address
The ARP protocol provides two basic functions:
1. ________________________________________________

 For
a frame to be placed on the LAN media, it must have a __________
destination MAC address.
 When a _____________ to the Data Link layer _________________ into a
frame, the node refers to a table in its memory to find the Data Link layer
MAC address that is mapped to the destination IPv4 address.


This table is called the ___________ or the ________________The ARP table is stored in the _____________ of the device.
2. Maintaining the ARP Table
 The ARP
table is _______________________
 There are _____________ that a device can ____________________


______ way is to _________________________________________
Another way is to __________________________ as follows…
 ARP
sends a Layer 2 broadcast to all devices on the Ethernet LAN. The
frame contains an ARP request packet with the IP address of the destination
host.

The _____________ receiving the frame that __________________________
_______________________ packet back to the sender as a ________________.
This response is then used to make a ___________________________
 These
dynamic entries in the ARP table are timestamped.
ARP Process- obtaining a MAC
address from a node on the
LOCAL network
3.
1.
2. Broadcast sent..
4. ARP table is populated
Now, what if the destination is
outside the local area
network?...
ARP Process – Destination outside the local Network

If the ________________ IPv4 host is ________
_______________ (determined by the source node’s
comparison of it’s IP to the destination IP)
the source node __________________________
_________ which is the gateway or next hop used to
reach the ultimate destination.
The ____________________________________
___________________ for frames containing an IPv4
packet addressed to hosts on other networks.
In the event that the gateway entry is not in the table,
the __________________ will send an __________
to _______________ associated with the IP address
of the ______________________-
ARP Process – Destinations
outside
the
local
Network
NOTE: In this scenario, host A expressly requests the MAC address of the
gateway (router’s interface)
4. ARP cache populated
2.
1.
3.
5. Ultimate destination IP and
local router’s MAC used
Proxy ARP– Destinations outside the local Network

There are circumstances under which a __________________________
______________________________________________ (ie- the host
does not expressly request the MAC address of the router’s interface)
 The
device sends ARP requests for IPv4 addresses not on the local
network instead of requesting the MAC address with the IPv4 address of
the gateway.

To provide a MAC address for these hosts, a ___________________ to
respond on behalf of remote hosts.
 This
means that the ARP cache of the requesting device will contain the ____
___________________________________________________________
 If proxy ARP is disabled on the router interface, these hosts cannot
communicate out of the local network.

When might proxy ARP be needed?
 IPv4
________________ whether the ________________________________
as the source.
 When a host believes that it is directly connected to the same network as the
destination host. This generally occurs when a host is configured with an
improper mask.
 When a ___________________________________________. Proxy ARP can
help devices on a network reach remote subnets.
ARP Process – Removing Address Mapping

For each device, an ARP _______________
_________________ that have not been used
for a specified period of time.
The
times differ depending on the device and its
operating system.

Commands may also be used to __________
____________ all or some of the entries in the
ARP table.
>______________
Deletes all entries
After an entry has been removed, the process for
sending an ARP request and receiving an ARP reply
must occur again to enter the map in the ARP table.
ARP Broadcasts Issues

Overhead on the Media
As
a broadcast frame, an ARP request is received
and processed by every device on the local network.
These broadcasts, generally, would probably have
minimal impact on network performance.

Security Risk
_____________________________________
___________ AKA ___________, is a technique
used by an attacker to ______________________
______________________________________

An attacker forges the MAC address of a device and then frames
can be sent to the wrong destination.
Prevent ARP spoofing by:
 ____________________ static ARP associations
 ____________________________________________
__________________________________