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Wireless Infrastructure - Chapter 18 > Chap 18 - Wireless Infrastructure > Flashcards

Chap 18 - Wireless Infrastructure Flashcards

1
Q

What are the two modes can wireless APs operate in?

A
  • Autonomous Mode
  • Lightweight Mode
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2
Q

What is Local MAC architecture?

A

When the AP does all the MAC functions (aka autonomous mode)

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3
Q

What is Split MAC architecture?

A

When the MAC functions are divided between the AP performs most of the real-time MAC functions and the WLC handles the management MAC functions.

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4
Q

What does CAPWAP stand for and what is it used for?

A
  • Control and Provisioning of Wireless Access Points
  • Tunneling protocol used to connect an AP to a WLC
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5
Q

What is a Centralized or Unified wireless LAN topology?

A

When the controller is located in a central location like a data center or a network core.

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6
Q

What kind of traffic goes across a CAPWAP tunnel?

A

Control plane and data plane traffic

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7
Q

How many APs can an enterprise WLC support?

A

Up to 6000

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8
Q

What should RTT be between an AP and the WLC?

A

Less than 100 msec

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9
Q

What is Embedded wireless topology?

A

It is when the WLC functionality resides on the switch itself.

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10
Q

How many APs can an embedded WLC support?

A

Up to 200

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11
Q

What is the Mobility Express Topology?

A

where a fully functional Cisco AP also runs software that acts as a WLC.

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12
Q

How many APs can Mobility Express support?

A

Up to 100

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13
Q

What are the 8 states that make up the Wireless Access Point State Machine?

A
  • AP Boots
  • WLC Discovery
  • CAPWAP Tunnel
  • WLC Join
  • Download image
  • Download config
  • Run State
  • Reset
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14
Q

What 3 things happen during the AP Bootup state?

A
  • AP receives power
  • AP runs small version of IOS
  • Receives an IP address (either DHCP or statically defined
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15
Q

What happens during the WLC Discovery state?

A

AP takes a number of steps to find a WLC

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16
Q

What happens during the CAPWAP Tunnel state, what protocol is the channel and how is authentication done?

A
  • AP attempts to build a CAPWAP tunnel with one or more controllers
  • The tunnel will provide a secure Datagram Transport Layer Security (DTLS) channel for subsequent AP-WLC control messages
  • The AP and WLC authenticate each other through an exchange of digital certificates.
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17
Q

What happens during the WLC Join state?

A
  • AP selects a WLC from a list of candidates and then sends a CAPWAP Join Request message to it.
  • WLC replies with a CAPWAP Join Response message
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18
Q

What happens during the Download Image state?

A
  • WLC informs the AP of its software release.
  • If AP software is a different release, the AP downloads a matching image from the controller, reboots to apply the new image, and then returns to step 1.
  • If the two are running identical releases, no download is needed.
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19
Q

what happens during the Download Config state and what 4 config parameters are included?

A
  • AP pulls configuration parameters down from the WLC and can update existing values with those sent from the controller
  • Settings include RF, SSID, security, and QoS parameters.
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20
Q

What happens during the Run state?

A

The AP and WLC provide a BSS and begin accepting wireless clients

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21
Q

What happens during the Reset state?

A
  • Existing client associations and CAPWAP tunnels torn down
  • AP then reboots and starts through the entire state machine again.
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22
Q

What determines the software release running on an AP?

A

The AP must run the software release that is running on the WLC.

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23
Q

What 3 scenarios would cause an AP to download a software release?

A
  • Version mismatch with the WLC
  • Code upgrade performed on the WLC
  • WLC fails forcing AP to join a different WLC
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24
Q

When upgrading a WLC how can you prevent a lengthy outage caused by APs downloading new code?

A
  • Download the new image to the controller but don’t reboot
  • Then perform pre-downloads to the AP’s They will continue to run the old image until the WLC reboots
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25
Q

What 3 methods of discovery do APs use when trying to build a list of WLCs?

A
  • Prior knowledge of WLCs
  • DHCP and DNS information to suggest some controllers
  • Broadcast on the local subnet to solicit controllers
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26
Q

What 4 sources can an AP use to build a list of WLCs and what does it do if those sources fail?

A
  • Broadcasts a CAPWAP Discovery Request on local wired subnet
  • Primed with up to 3 WLC addresses kept in NVRAM or up to 8 WLCs from previously joined WLC
  • DHCP option 43
  • DNS query for CISCO-CAPWAP-CONTROLLER. localdomain
  • If previous steps unsuccessful reset and try again
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27
Q

Once the AP has a list of WLCs what 3 steps does it go through to decide on one?

A
  • If AP has primed addresses it will attempt to join primary, secondary, tertiary in order
  • Joins the Master WLC
  • Joins the least loaded WLC
28
Q

What could be one reason a WLC refuses an AP’s request to join?

A

The WLC license or platform determines the max number of AP’s it’s allowed to manage. That max number may have been reached.

29
Q

What can be done to mitigate a situation where there are more APs than the WLC is allowed and what is the default priority?

A
  • AP’s can be assigned a priority - low, medium, high, critical. The WLC will kick off lower priority APs to allow higher priority ones to join
  • Default is Low
30
Q

What is the default keepalive interval that APs send to WLCs?

A

30 seconds

31
Q

What does the AP do if the WLC doesn’t answer a Keepalive?

A
  • Sends 4 more keepalives at 3 second intervals
  • If still no answer the AP finds another WLC
32
Q

By adjusting timers how quickly can an AP detect a failed controller?

A

6 seconds

33
Q

How long does it take an AP to detect a down controller if the default timers are in use?

A

As little as 35 seconds

34
Q

What are the 8 Access Point Modes?

A
  • Local
  • Monitor
  • FlexConnect
  • Flex-Bridge
  • Bridge
  • Rogue Detector
  • Sniffer
  • SE-Connect
35
Q

What is the Local mode, what does it normally do, and what does it do when its not transmitting?

A
  • Default mode
  • Provides one or more BSSs
  • When not transmitting it scans other channels to measure level of noise, level of interference, rogue devices, matches IDS events
36
Q

What is Monitor mode and what are 3 things it checks for?

A
  • Does not transmit
  • Receiver enabled to act as dedicated sensor
  • The AP checks for IDS events, rogue access points, and location of stations through location-based services.
37
Q

What is FlexConnect mode?

A

An AP at a remote site can locally switch traffic between an SSID and a VLAN if its CAPWAP tunnel to the WLC is down

38
Q

What is Sniffer mode?

A

An AP dedicates its radios to receiving 802.11 traffic from other sources, much like a sniffer or packet capture device. The captured traffic is then forwarded to a PC running network analyzer software such as LiveAction Omnipeek or Wireshark,

39
Q

What do Rogue Detectors do?

A

An AP dedicates itself to detecting rogue devices by correlating MAC addresses heard on the wired network with those heard over the air. Rogue devices are those that appear on both networks.

40
Q

What is Bridge mode and what 2 things can APs in Bridge Mode do?

A
  • An AP becomes a dedicated bridge (point-to-point or point-to-multipoint) between two networks.
  • Two APs in bridge mode can be used to link two locations separated by a distance.
  • Multiple APs in bridge mode can form an indoor or outdoor mesh network.
41
Q

What is Flex+Bridge mode?

A

It’s when FlexConnect operation is enabled on an AP in a mesh network

42
Q

What is SE-Connect mode?

A
  • AP does spectrum analysis on all wireless channels.
  • Engineer remotely connects a PC running software such as MetaGeek Chanalyzer or Cisco Spectrum Expert to the AP to collect and analyze the spectrum analysis data to discover sources of interference.
43
Q

What is a Radiation Pattern?

A

It is a plot that shows the relative signal strength around an antenna

44
Q

What is the ‘H’ Plane and what does it show?

A
  • Horizontal plane
  • Shows top-down view of the radiation pattern through the center of the antenna
45
Q

What is the ‘E’ Plane and what does it show?

A
  • Elevation Plane
  • It lies vertically along the elevation of the sphere
  • It shows a side view of the same radiation pattern.
46
Q

What is a Polar Plot made up of, and what does it measure?

A

A polar plot contains concentric circles that represent relative changes in the signal strength, as measured at a constant distance from the antenna.

47
Q

What do Antennas do?

A

They add gain to the signal by shaping the RF energy as it is propagated into free space.

48
Q

What is gain of an antenna a measure of?

A

How effectively an antenna can focus RF energy in a certain direction.

49
Q

Which antenna produces higher gain - Omni-directional or Directional?

A

Directional antennas

50
Q

What is Beamwidth and what unit of measurement is used to calculate it?

A

It’s a measure of the antenna’s focus. Beamwidth is normally listed in degrees for both the H and E planes.

51
Q

What 2 components make up a wave?

A
  • Electrical Field
  • Magnetic Field
52
Q

What is Polarization?

A
  • The electrical field wave’s orientation, with respect to the horizon,
  • Antennas that produce vertical oscillation are vertically polarized; those that produce horizontal oscillation are horizontally polarized.
53
Q

What is the orientation of the Magnetic field?

A

The magnetic field is oriented at 90 degrees from the electrical field wave.

54
Q

Why does polarization matter?

A

Antenna polarization at the transmitter must be matched to the polarization at the receiver. If the polarization is mismatched, the received signal can be severely degraded.

55
Q

What are the 2 types of antennas?

A
  • Directional
  • Omnidirectional
56
Q

What does an Omnidirectional Antenna look like, which way does it propogate a signal, what is its pattern shaped like, and what kind of gain does it have?

A
  • Usually made in the shape of a thin cylinder
  • Tends to propagate a signal equally in all directions away from the cylinder
  • Donut-shaped pattern that extends further in the H plane than in the E plane
  • Relatively low gain
57
Q

What is an Omnidirectional Antenna best suited for?

A

Best suited for broad coverage of a large room or floor area, with the antenna located in the center.

58
Q

What type of antenna is a Dipole antenna, what is it made up of, what does it do, and what is its gain?

A
  • A type of omnidirectional antenna
  • It has 2 wires that radiate RF when alternating current is applied
  • Has a gain of around +2 to +5 dBi.
59
Q

What kind of gain does an integrated omnidirectional antenna have in the 2.4GHz and 5 GHz bands?

A
  • 2 dBi in the 2.4 GHz band
  • 5 dBi in the 5 GHz band.
60
Q

What are directional antennas used for?

A
  • Elongated indoor areas, such as the rooms along a long hallway or the aisles in a warehouse.
  • Also outdoor areas out away from a building or long distances between buildings.
61
Q

Can directional antennas be used to reduce an AP’s cell size?

A

Yes, if they are mounted against a ceiling, pointing downward, they can cover a small floor area to reduce an AP’s cell size.

62
Q

What is a patch antenna?

A

A directional antenna mounted against a wall that radiates outward.

63
Q

What is the gain for a patch antenna?

A

Patch antennas have a typical gain of about 6 to 8 dBi in the 2.4 GHz band and 7 to 10 dBi at 5 GHz.

64
Q

What type of antenna is the Yagi antenna, what is it made up of, what does the outer case look like, what what gain does it have?

A
  • Directional antenna
  • Made up of several elements of increasing size
  • Outer case shaped like a cylinder
  • 10 to 14 dBi gain
65
Q

What type of antenna is a Dish antenna, what is it made up of, and what is its gain?

A
  • Directional antenna
  • Parabolic dish that reflects signals to the antenna in the middle
  • Gain of 20-30 dBi
66
Q

What does DTLS stand for?

A

Datagram Transport Layer Security

Wireless Infrastructure - Chapter 18 (3 decks)

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