1. Modified by Profs. Chen and Cappellino
Chapter 9- Ethernet
Modified by Profs. Chen and Cappellino

2. 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)

3. 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 (_______________).

4. 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 ______________________________

5. 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 ______________________________ ____________________________________

6. Logical Link Control Sublayer of the Data Link Layer
IEEE 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.
_________________________________

7. 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
The MAC layer _____________________ to the Layer 3 PDU.
It __________________________ between the transmitting and receiving nodes.
Each __________________________________________ that enables a frame to be delivered to a destination node.
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.

8. 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

9. 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.

10. 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

11. 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.

12. 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 _____________________________________

13. 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).
_______________________________________________ _______________________________________

14. Review- what field is it?

15. 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?

16. 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

17. 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 there is ___________________________________
If 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.

18. 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 to 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:
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: How would be calculate the DECIMAL VALUE OF 1011?

19. 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.

20. 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 (source) requests a web page from the server at IP address
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?

21. 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 ___________________________

22. 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".

23. 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.
Let's take a look at the process...

24. CSMA/CD – The Process Carrier Sense Multi-access
____________________________________________ 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.

25. 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.

26. 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 _________ _______________________

27. Hubs and Collision Domains Graphic
Need something more than CSMA/CD to control collisions in a large networked environment
Stay tuned…

28. 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- _____________

29. Segmentation with switch
How many collision domains do we have?

30. Segmentation with router
How many collision domains do we have here?

31. 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.

32. 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 _________________________________

33. 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.

34. 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.

35. 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 _________ _________________________________________________________________________

36. 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 ____________.

37. 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…

38. Overview of Ethernet Physical Layer
The ____________ between standard Ethernet, Fast Ethernet, Gigabit Ethernet, and 10 Gigabit Ethernet __________________________
Ethernet is covered by the IEEE 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

39. 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 (star topology)
10 Mbps Ethernet - ________________
______________________ is typically used today
10BASE-T uses ___________________ and is ___________ at each end with an 8-pin _____________________
It uses Manchester-encoding over two unshielded twisted-pair cables.
It uses a _______________________
It could be up to __________________________________ (or repeater)
The 10BASE-T links connected to a switch can support either half-duplex or full-duplex operation.

40. 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 100BASE-TX, 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

41. 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
1000Base-T Ethernet
1000Base-SX and 1000Base-LX using Fiber
More to come…

42. 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

43. 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

44. 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 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.

45. 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

46. 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.

47. 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

48. Using Switches- with _____________________
_____________ 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?

49. 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

50. 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 __________________

51. Stay tuned to the next course…
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…

52. 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.

53. 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.

54. Switch Operation 3. ____________________ 4. __________________________
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 _____________________________.
If a frame fails a CRC check
An additional reason for filtering a frame is ____________________.
A switch has security settings for _______________________ to and/or from selective MAC addresses.

55. 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.

56. ARP Process- obtaining a MAC address from a node on the LOCAL network3. 1.
2. Broadcast sent..
4. ARP table is populated
Now, what if the destination is outside the local area network?...

57. 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 ______________________-

58. 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.
Broadcast sent
5. Ultimate destination IP and local router’s MAC used

59. 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.

60. 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.

61. ARP Broadcasts Issues Overhead on the Media Security Risk
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
____________________________________________ __________________________________