18. Wireless Infrastructure Flashcards
What are the 2 modes a Cisco AP can operate in?
- Autonomous
- Lighweight
What is the difference between the 2 Cisco AP modes?
The autonomous is self-sufficient and standalone
The lightweight need something bigger to operate
What does a autonomus AP need?
A own IP address
What does a lightweighted AP need to become functional?
A WLC
What is a split-MAC architecture?
Where the AP handles the realtime 802.11 processes and the WLC the management functions
What is transported through CAPWAP tunnels?
Data and control traffic between AP and WLC
What is a centralized or unified wlan topology?
When the WLC is placed in a central location, usually the data center or near the network core
Why is the maximum delay for the RTT between an AP and WLC?
100 ms
What is a embedded wlan topology?
When the WLC is embedded in the access layer switch
How many APs does a Cisco embedded WLC support?
200
What is the disadvantage of a embedded topology?
Traffic destined to a central location will be decapsulated at the access layer.
What is a mobility express wlan topology?
Where the WLC software runs on a AP
How many APs does a Cisco mobility express WLC support?
100
How is the sequence of CAPWAP states called?
State machine
What are 8 most common CAPWAP states of an AP?
- AP boots (done with a small IOS image)
- WLC discovery
- CAPWAP tunnel
- WLC join
- Download image
- Download config
- Run state
- Reset
What happens in the WLC join state?
AP selects a WLC from the candidate list and sends a CAPWAP join request.
WLC replies with a CAPWAP Join Reponse
What happens in the Download image state?
The WLC informs the AP of its software release
If not equal, the AP downloads an image of the WLC, reboots and starts at step 1 again
What happens in the Download config state?
AP pulls config parameters from the WLC and updates values as RF, SSID, security and QoS
What happens in the Run state state?
Once AP is full initialized the WLC places it in the run state. WLC and AP begin providing a BSS and accept clients
What can be done to prevent AP downtime due to OS updates?
Newer software can be downloaded on the WLC, but not rebooted. This gives the APs time to download it first as well
What are the methods an AP takes to discover a WLC?
- Broadcast on local subnet
- Prior knowledge
- DHCP or DNS
What are the steps an AP takes to discover a WLC?
- AP sends a CAPWAP discovery request on local subnet and if present a WLC replies with a CAPWAP Discovery Response
- AP can prime 3 controllers that are saved in the nonvolatile memory. 8 Previous WLCs are saved
- DHCP can send a DHCP option 43
- AP resolves CISCO-CAPWAP-CONTROLLER-domainname
- If no steps are succesful the AP resets and starts at step 1 again
What is the selecting WLC process of an AP?
- Previously joined or primed first
- Tries to discover. If there is a master WLC it will respond to the request
- Joins the least loaded WLC
What can be done to have a WLC accept an AP although his capacity is reached?
Change the priority of an AP. A WLC will try to accomodate as many high prio APs as possible
What are the 4 priority states of an AP?
- Low
- Medium
- High
- Critical
What can be done to spread AP traffic when a WLC goes down?
Spread by adding the primaire, secundary and tertiary command
What is the default AP keepalive time?
30 seconds
What happens when a WLC does not respond on the APs keepalive?
The AP sends 4 more keepalives with a 3 sec interval
What is the keepalive timer range?
1-30
What is the fast keepalive timer range?
1-10
What does WLC support for high availability?
Statefull switchover. The active WLC synces with a standby WLC
What are the 8 AP operating special modes from a WLC?
- Local
- Monitor
- FlexConnect
- Sniffer
- Rogue detector
- Bridge
- Flex+Bridge
- SE-connect
What happens in the Local operating mode?
Default mode that offers one or more BSSs on a specific channel. When it is not transmitting it scans the other channels to measure the level of noise, interference and IDS events
What happens in the Monitor operating mode?
AP does not transmit, but receiver is enabled to act as a dedicated sensor. Checks IDS events, roque access points and determines the position of stations through location based services
What happens in the FlexConnect operating mode?
No WLC needed! An AP at a remote site can locally switch traffic between an SSID and VLAN if CAPWAP is down
What happens in the Sniffer operating mode?
AP dedicates its radios to receiving 802.11 traffic from other sources and forwards to a analyzer
What happens in the Rogue detector operating mode?
AP dedicates itself to detect rogue devices by correlating MAC addresses heard on the wired network with those heard in the air. Rogue devices are those that appear on both networks
What happens in the Bridge operating mode?
AP becomes a dedicated bridge (p2p or P2M) between 2 networks. Can form an indoor or outdoor mesh network
What happens in the Flex+Bridge operating mode?
Flexconnect activated on a mesh AP
What happens in the SE-connect operating mode?
AP dedicates its radios to spectrum analyses on all wireless channels.
What is a radiation pattern?
A plot that will show the relative signal strength around an antenna
How is the horizontal plane called?
H-plane (xy-as) Azimuth
How is the vertical plane called?
E-plane (xz-as) Elevation
What is polarization?
The orientation of the electrical waves. The polarization must match on transmitter and receiver
What are the two basic type of antennas?
- Omnidirectional
- Directional
What is a omnidirectional antenna?
A thin cylinder. Signal will go out all ways expcept in the lenght. More signal in the H-plane
What is the typical gain of a omnidirectional antenna?
2dBi on 2,4GHz
5dBi on 5GHz
What is a directional antenna?
Have higher gain than omnidirectional because they focus the RF energy in one general direction
What is the typical gain of a patch antenna?
6-8dBi on 2,4GHz
7-10dBi on 5GHz
What is the typical gain of a Yagi antenna?
10-14dBi
What is the typical gain of a Dish antenna?
20-30dBi
