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ag-CCNA > 11 - Wireless LANs > Flashcards

11 - Wireless LANs Flashcards

1
Q

What is the IEEE number for Ethernet?

A

802.3

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2
Q

What is the IEEE number for Wireless?

A

802.11

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3
Q

Why are 802.11 WLANs always half duplex?

A

Because transmissions use the same frequency only one station can transmit at any time, otherwise collisions occur

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4
Q

What is a BSS?

A

Basic Service Set. A wireless service area involving a group of devices formed around a fixed device

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5
Q

What mode does an AP operate in?

A

Infrastructure mode

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6
Q

What is a BSA?

A

Basic Service Area. The bounding area of the BSS where the APs signal is usable

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7
Q

What does an AP use to advertise the existence of the BSS?

A

BSSID

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8
Q

What is a BSSID?

A

Unique BSS Identifier, based on the APs own radio MAC address

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9
Q

What is an SSID?

A

Service Set Identifier. A human readable name tag that identifies a wireless service

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10
Q

What is an association and how is it formed?

A

A membership with the BSS. A potential client must send an association request to the AP which it can grant or deny

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11
Q

What does the 802.11 standard refer to as the upstream wired Ethernet as?

A

The DS (Distribution System)

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12
Q

What is an AP effectively doing when it serves multiple SSIDs?

A

Trunking VLANs over the air to wireless clients

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13
Q

What is an ESS and what is it used for?

A

Extended Service Set.

For interconnecting APs placed at different geographic locations with a switched infrastructure

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14
Q

What is roaming with respect to APs?

A

Moving from one AP to another automatically

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15
Q

What must a client do as it roams from one AP to another?

A

Scan available channels to find the new AP (and BSS) to roam toward

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16
Q

True/False: In ESS each AP offer its own BSS on its own channel, even with the same SSID

A

True

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17
Q

What is an IBSS?

A

Independent BSS.

Allows two or more wireless clients to communicate directly with each other with no other means of network connectivity

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18
Q

What is another name for an IBSS?

A

Ad hoc WLAN

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19
Q

How could you extend the range of a wireless network?

A

Add an AP in repeater mode

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20
Q

What is a WGB and what is it used for?

A

Workgroup Bridge.

It can be used to connect a device’s wired network adapter to a wireless network

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21
Q

What are the two common types of WGBs?

A
  1. uWGB (universal). A single wired device can be bridged to a wireless network
  2. WGB. Cisco proprietary implementation allows multiple wired devices to be bridged
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22
Q

What is an Outdoor Bridge?

A

APs can be configured to act as bridges for LANs. Outdoor bridged links involve special purpose antennas to achieve this over long distances

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23
Q

What is a Mesh network?

A

Interconnected wireless APs in Mesh mode instead of being interconnected with switched infrastructure (Ethernet)

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24
Q

What is the frequency of a wave measured as?

A

The number of times a signal makes one complete up and down cycle in 1 second

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25
Q

What is another way of describing Hz / Hertz?

A

Cycles per second

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26
Q

What frequency range category are 5Ghz and 2.4Ghz wireless in?

A

Microwave

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27
Q

What is an interesting property of 5ghz band channels?

A

They are non overlapping, so APs can use any channel number without affecting APs using any other channel numbers

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28
Q

What channels must be used in 2.4Ghz to avoid overlap between adjacent channels?

A

1, 6, 11

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29
Q

What is the primary function of an access point?

A

Bridge wireless data from air to a wired network

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30
Q

What is an Autonomous AP?

A

Self contained AP, fully equipped with both wired and wireless hardware

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31
Q

How are Autonomous APs natural extensions of a switched network?

A

They connect wireless SSIDs to wired VLANs at the access layer

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32
Q

True/False: Two clients connected to an AP cannot talk to each other without going through the full network connected to the AP?

A

False. They can communicate directly through the AP

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33
Q

True/False: SSIDs and their VLANs must be extended at Layer 2

A

True

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34
Q

What is Cisco Prime Infrastructure?

A

An AP management platform

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35
Q

What is Cisco Meraki?

A

Cloud based AP management platform

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36
Q

What is a WLC and why are they good?

A

Wireless LAN Controller. They separate out the management functions required of APs (RF management, auth, security) into a separate centralized controller to make autonomous APs easier to manage

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37
Q

What is a lightweight AP?

A

An AP that only performs the real-time functions of 802.11 such as sending and receiving frames, MAC etc

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38
Q

True/False: Generally a lightweight AP cannot usually operate on its own

A

True

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39
Q

What is Split MAC architecture?

A

When management and normal operations of an AP are split out into WLC and lightweight APs

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40
Q

What is CAPWAP?

A

Control and Provisioning of Wireless Access Points.

A tunneling protocol used to encapsulate data between the LAP and WLC within new IP packets

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41
Q

What are the two separate tunnels that are part of the CAPWAP relationship?

A

CAPWAP Control messages

CAPWAP Data

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42
Q

What are CAPWAP control messages used for?

A

Carrying authenticated/encrypted exchanges used to configure an AP and manage its operations.

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43
Q

What are CAPWAP data messages used for?

A

Packets traveling to and from wireless clients that are associated with the AP. Not encrypted by default.

44
Q

What is DTLS?

A

Datagram Transport Layer Security. Used under CAPWAP when data encryption is enabled for an AP to protect packets

45
Q

What legacy Cisco proprietary solution is CAPWAP based on?

A

LWAPP. Lightweight Access Point Protocol

46
Q

What must every AP and WLC authenticate with each other using?

A

Digital Certificates e.g. X.509

47
Q

True/False: An AP and WLC cannot be separated logically or geographically, they must be in the same subnet / location

A

False. CAPAP tunneling allows them to be separated and breaks dependence on Layer 2 connectivity between them

48
Q

Why are trunk links not needed for an AP using CAPWAP?

A

Because all VLANs its supports are encapsulated and tunneled as Layer 3 IP packets rather than individual L2 VLANs

49
Q

What is Unified / Centralized WLC deployment?

A

When you place the WLC in a central location to maximize the number of APs joined to it

50
Q

How many APs does a WLC typically support?

A

6000

51
Q

What is a Cloud based WLC deployment and how many APs would it typically support?

A

Where the WLC exists as a virtual machine rather than physical device e.g inside a data center in a private cloud.

Around 3000

52
Q

What is an Embedded WLC deployment and where would you use it?

A

When the WLC is co-located with a stack of switches.

Used on small campuses or distributed branch locations where the number of APs is small. Can support around 200 APs

53
Q

What is Cisco Mobility Express WLC deployment and where would you use it?

A

WLC function co-located with an AP that is installed at the site. Supports around 100 APs.

Small scale environments where you might not need to invest in dedicated WLCs at all

54
Q

What is Local mode for a lightweight AP?

A

Default lightweight mode that offers one or more functioning BSSs on a specific channel.

When not transmitting AP will scan to measure noise, interference, rogue devices etc

55
Q

What is Monitor mode for a lightweight AP?

A

The AP does not transmit at all but receiver enabled to check for IDS events, rogue access points and positions of stations, etc

56
Q

What is FlexConnect mode for a lightweight AP?

A

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

57
Q

What is Sniffer mode for a lightweight AP?

A

An AP that dedicates its radios to receiving 802.11 traffic from other sources and forwards it to a host running network analyzer software

58
Q

What is Rogue detector mode for a lightweight AP?

A

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

59
Q

What is Bridge mode for a lightweight AP?

A

AP becomes a dedicated bridge (PtP or PtMP) between two networks. Can be used to link two locations separated by distance. Multiple APs in bridge mode can form a mesh network

60
Q

What is Flex+Bridge mode for a lightweight AP?

A

FlexConnect operation enabled on a mesh AP

61
Q

What is SE-Connect mode for a lightweight AP?

A

AP dedicated to spectrum analysis on all wireless channels

62
Q

With respect to Security, what should a client do with management frames sent by an AP?

A

Authenticate them to ensure the AP is actually a legitimate expected AP

63
Q

What is an AP group key used for?

A

A key maintained by the AP that it uses when it needs to send encrypted data to all clients in its cell at one time, with each client using the same group key to decrypt the data

64
Q

What is a MIC?

A

Message Integrity Check that prevents against data tampering

65
Q

What cipher algorithm does WEP use?

A

RC4

66
Q

What type of security method is WEP?

A

Shared-key

67
Q

How does an AP test the clients knowledge of a WEP key?

A

Sends it a random challenge phrase that it must encrypt with the WEP key and return the result to the AP

68
Q

What is EAP?

A

Extensible Authentication Protocol.

Defines a set of common functions that actual methods can use to authenticate users

69
Q

What is the difference between Open/WEP authentication at the AP and EAP?

A

With 802.1x the client uses open authentication to associate with the AP, then the actual client authentication process occurs at a dedicated authentication server

70
Q

What is an 802.1x Supplicant?

A

The device requesting access

71
Q

What is an 802.1x Authenticator?

A

The network device that provides access to the network (usually WLC)

72
Q

What is an 802.1x Authentication Server?

A

The device that takes the user / client credentials and permits or denies network access based on a user db and policies (e.g. RADIUS server)

73
Q

What is LEAP?

A

Lightweight EAP.

Protocol that tried to overcome WEP weaknesses by using dynamic WEP keys that changed frequently but was still vulnerable

74
Q

What is EAP-FAST?

A

EAP Flexible Authentication by Secure Tunneling.

Authentication credentials protected by passing a PAC (Protected Access Credential) between the AS and the supplicant. Uses inner and outer authentication for both authenticating the supplicant and the end user through the resulting tunnel

75
Q

What is a PAC?

A

Protected Access Credential.

A form of shared secret generated by the AS and used for mutual authentication

76
Q

What is PEAP?

A

Protected EAP. Has inner and outer authentication like EAP-FAST, but the AS presents a digital certificate to authenticate itself with the supplicant in the outer authentication.

If the supplicant is happy, it will form a TLS tunnel to be used for subsequent inner client authentication and encryption key exchange

77
Q

What is EAP-TLS?

A

EAP-TLS goes a step further from relying on clients to authenticate digital certificates presented by the AS by requiring certificates on the AS and on every client device.

Highly secure but complex. Requires a PKI to implement effectively for certificate supply and revocation

78
Q

What is TKIP?

A

Temporal Key Integrity Protocol.

Contains TKIP sequence counter to prevent frame replay attack. Now deprecated. Used in WPA, WPA2

79
Q

What is CCMP?

A

Counter/CBC-MAC protocol consisting of two algorithms

  • AES Counter mode encryption
  • Cipher Block Chaining Message Authentication Code used as a MIC

Used in WPA, WPA2

Requires devices to have hardware support (WPA2)

80
Q

What is GCMP?

A

Galois/Counter Mode protocol consisting of two algorithms

  • AES counter mode encryption
  • Galois MAC used as a MIC

Used in WPA3

81
Q

What are PMFs?

A

Protected Management Frames used to secure important 802.11 management frames between APs and clients

82
Q

What is SAE?

A

Simultaneous Authentication of Equals

83
Q

What two client modes do all WPA versions support?

A
  • PSK (Pre Shared Key) aka Personal mode

- 802.1x aka Enterprise mode

84
Q

How does PSK mode function?

A

They secret key string is never sent over the air. A four way handshake procedure takes place that uses the PSK to construct and exchange encryption key material, then subsequently authenticate the client and secure frames

85
Q

How does WPA3 avoid the eavesdropping attacks associated with WPA and WPA2 Personal (PSK) modes?

A

By strengthening key exchange between clients and APs using SAE in which the client and AP can initiate the authentication process equally and simultaneously.

WPA3 also uses forward secrecy to prevent attackers being able to un-encrypt data that has already been transmitted over the air

86
Q

What does an AP map each VLAN to?

A

A WLAN and BSS

87
Q

What must the wired Ethernet interface on a lightweight AP be paired with to be fully functional?

A

A WLC

88
Q

What are multiple VLANs extended from the WLC to the AP carried over?

A

CAPWAP tunnel

89
Q

What does a lightweight AP need in terms of a link to connect to network infrastructure and terminate its end of the tunnel?

A

An Access link

90
Q

How are ports and interfaces distinguished differently when talking about WLCs?

A

For WLCs a port refers to physical connections made to an external wired or switched network.

Interfaces refers to logical connections made internally within the controller

91
Q

What is a WLC Service port used for?

A

Out of band management, system recovery, and initial boot functions.

Always connects to switch port in Access mode

92
Q

What is a WLC Distribution System port used for?

A

Normal AP and management traffic.

Usually connects in 802.1Q Trunk mode

93
Q

What is a WLC Redundancy port used for?

A

To connect to a peer controller for HA (high availability)

94
Q

True/False: The WLC service port only supports a single VLAN

A

True

95
Q

Which WLC ports do the CAPWAP tunnels extending to each AP pass across?

A

Distribution System ports

96
Q

What is name for the wired system that connects APs together?

A

Distribution System (DS)

97
Q

What mode should Distribution System ports on a WLC always operate in and why?

A

802.1Q Trunking mode.

Because they must carry data that is associated with many different VLANs

98
Q

What is a LAG?

A

Link Aggregation Group.

A bundle of WLC distribution ports configured to operate as a single logical group / EtherChannel, with traffic being able to be load balanced across the ports.

99
Q

What is a WLC Management interface?

A

Used to terminate CAPWAP tunnels and for normal management traffic such as:

  • RADIUS
  • WLC to WLC communication
  • Web / SSH sessions
  • SNMP
  • NTP
100
Q

What is a WLC Virtual interface?

A

Used for client facing operations.

It is the IP address facing wireless clients when the control is relaying DHCP requests, client web auth and supporting client mobility

101
Q

What is a WLC Service port interface?

A

Interface bound to a service port and used for out of band management

102
Q

What is a WLC Dynamic interface?

A

Connects VLAN to a WLAN

103
Q

What type of controller interface type is used to connect a VLAN to a WLAN?

A

Dynamic interface

104
Q

What class of address should you configure on a WLC virtual interface?

A

Unique nonroutable IP such as a private address

105
Q

Why should each controller in a mobility group use the same virtual interface address?

A

Appear to operate as a cluster as clients roam from controller to controller

106
Q

True/False: You only need one dynamic interface to support multiple WLANs

A

False.

You must create one dynamic interface for each WLAN offered by the controller’s APs and map the interface to the WLAN

107
Q

What is the downside of creating too many WLANs?

A

A channel can be starved of any usable airtime. Clients will have difficulty transmitting their own data because the channel is too busy with beacon transmissions coming from the AP

ag-CCNA (21 decks)

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