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Wireless - midterm
Wireless midterm
| Question | Answer |
|---|---|
| Distribution System | Interconnects BSSs to LANs, normally wired but can be wireless. |
| BVI | Bridge Virtual Interface, virtual bridge between wireless and wired interfaces. Also used for management of the AP. |
| How many IP addresses in an AP? | One, assigned to the BVI for management. |
| 4 Main steps to configuring AP? | 1(Configure BVI), 2(Configure SSID), 3(Configure Wireless Radio), 4(Configure wired/wireless sub-interfaces). |
| Basic Service Set | One or more STA associated with an access point, identified by the BSSID (radio MAC ID) |
| Extended Service Set | One or more BSSs interconnected by a distribution system, identified by SSID. |
| Relationship between VLAN and SSID? | Can associate an SSID to a specific VLAN sort of like associating ports to a VLAN. |
| AP | Access Point: provides wireless connectivity and connection to DS. |
| STA | Wireless Station: device that contains 802.11 compatible interface (laptops, wifi adaptors) |
| BSA | Basic Service Area: also called Cell, area which the AP provides service, defined by signal strength |
| IBSS | Independant BSS: self-contained, no DS, peer-to-peer (ad hoc). |
| Autonomous AP vs. Split MAC AP | Autonomous AP is like a normal AP, split MAC w/ Controller has controller doing most of the work with the lightweight AP doing little. |
| BVI Config | int bvi 1; ip address; no shut |
| SSID Config | dot11 ssid (name); vlan (#); authentication; guest-mode |
| Radio Config | int dot11radio 1; ssid (name); channel; station-role (root|repeater) access point; no shut |
| Sub Interface Config | int (dot11radio 1.(#)| fa0.#); encapsulation dot1q (vlan#) [native]; bridge-group (#) |
| Setting Up Repeater | SSID CONFIG#infrastructure-ssid RADIO CONFIG#station-role repeater #dot11 extension aironet #parent 1 (parent MAC ID) |
| Setting up Standby | (gc)#iapp standby mac-address (parent MAC ID) |
| Wavelength | The distance between two identical points on a wave (ex: peak to peak) |
| Frequency | Number of RF signal cycles within a specified time interval, measured in Hz. |
| How are Wavelength and Frequency related? | Smaller wavelength = Larger Frequency |
| Phase | The difference in alignment when comparing two or more signals that share the same frequency. |
| Amplitude | Signal Strength/Power |
| Transmit Amplitude | Initial amplitude that leaves the radio transmitter. |
| Receive Amplitude | Final amplitude that is received by STA, lowered by attenuation. |
| Signal Gain | Two sources of gain for RF, an amplifier which increases the power or an Antenna which concentrates the signal in a smaller area. Measured in dB. |
| Signal Loss | Some loss occurs due to cabling, as well as various wave propagation effects for RF. Measured in dB. |
| Part of the power of the signal gets taken into the object which it is interacting with. | Absorption |
| When a wave hits a smooth object the wave may bounce in another direction. | Reflection |
| RF signal encounters some type of uneven surface and is reflected into multiple directions. | Scattering |
| Bending of an RF signal as it passes through a medium causing the direction of the wave to change. | Refraction |
| Bending and the spreading of an RF signal when it encounters an obstruction. | Diffraction |
| Decrease of amplitude, or signal strength. Occurs on wire and in air. | Attenuation |
| Loss of signal strength caused by the natural spreading of the waves. | Free Space Path Loss |
| Two or more paths of a signal arriving at a receiving antenna at basically the same time. | Multipath |
| What are the effects of Multipath? | Since waves will be out of phase it can cause up/down fade, complete nulling, and data corruption. |
| How does frequency/wavelength affect absorption? | Higher frequency/Shorter wavelength is more easily absorbed by materials (won't pass through). |
| 802.11i | specifies security mechanisms for wireless networks (WPA2) to fix broken WEP. |
| Which 802.11 amendments use 5GHz band? | a, n, ac |
| Which 802.11 amendments use 2.4GHz band | b, g, n |
| Wireless governing bodies? | IEEE, Wi-Fi Alliance, FCC/CRTC |
| What are the channels used in 2.4GHz band? | 1, 6, 11 |
| What are the channels used in lab on 5GHz band? | 36, 40, 44, 48, 52, 56, 60, 64 |
| How do APs get power in lab? | PoE from power injectors in the floor. |
| Which layer does an AP operate on? | Layer 2 |
| Wireless Networking functions primarily at which OSI layers? | Layer 1 and 2 |
| What modes can a Bridge be in? | Root, Non-root, Repeater, Root/non-Root w/ clients, AP, WGB |
| Lightweight “Thin, mesh” AP | Low cost, centrally managed by controller. |
| Repeater | Extends the radio frequency cell, reduce throughput by 50%/per wireless link. Also requires 50% overlap of the cell. Recommended no more than 2 hops per cell. |
| Multi-Channel Architecture | Separate channel per cell, reduce cell size for capacity (user more cells) |
| Sectorized Array Arch | Sectored antenna system, add sectors for capacity. Picture looks like a rainbow flower. |
| Main use of Bridges | Connect two or more wired LAN’s, usually located within separate buildings, to create one large LAN. |
| Root Bridge | Parent, allows non-Root(children) bridge devices to associate. Does not communicate with other Roots. |
| Non Root Bridge | Child, associates with Root(parent). Will not communicate with other non-root unless other device is communicating with a parent. |
| Rugged devices | Literally rugged, can suffer the outdoors. |
| Point-to-Point Bridge | max: 40km (25mile), line of sight, obstacles cause problems. Acts as a single segment. Can aggregate up to 3 links with cisco Etherchannel. |
| Point-to-Multipoint Bridge | Typically omni-directional used at main site, directionals at remote sites. LoS only needs to be maintained to the main site. All LANs appear as a single segment. |
| How does wireless bridging go past 1.6km (1 mile)? | Violating the 802.11 timing standard for ACKs. |
| Recommended Cell overlap? | 10% - 15%, need overlap for seamless roaming |
| Redundancy with different vendors. | Same channel and data rates, only one AP can be talking at a time in this situation. Only provides redundancy no extra throughput. |
| Redundancy with Hot-Standby | No load balancing, monitors the primary AP on the same channel and if it fails will take over. |
| 802.11F | Deals with IAPP (Inter-Access Point Protocol) which is used for roaming. No standard is yet set for this. |
| Roaming process | Moving away from AP signal strength lowers but strength of neighboring AP increases. Client initiates roaming (re-association). |
| Re-Association Process | New AP confirms association, New AP informs Old AP of association, New AP updates MAC address tables on switches, new AP sends MAC address of client to Old AP so all switches can update tables. |
| Roaming Signal Strength Threshold | When signal strength falls bellow threshold client will try to find a better AP. Used to prevent client switching between 2 strong signals. |
| Roaming Wait Threshold | Client will will at least a certain per-defined time after connecting to an AP before searching for better access. |
| Dynamic Rate Switching | As client gets further from AP it will shift to lower data rates to improve reliability. |
| Default SSID | tsunami |
| Reset AP to Factory Defaults | 1:Disconnect Power 2:Press+hold MODE button while power reconnected 3:Hold MODE button until LED turns amber |
| Connecting to AP | console, Telnet 10.0.0.1/27, password = Cisco |
| WEP | Wired Equivalent Privacy. Broken weak legacy encryption, <5 minutes to crack. |
| TKIP | Temporal Key Integrity Protocol. Interim solution to replace WEP without requiring the replacement of legacy hardware. Medium security. |
| AES | Advanced Encryption Standard. Currently used worldwide. Strong. |
| EAP | Extensible Authentication Protocol. Authentication framework frequently used in wireless networks and Point-to-Point connections. |
| What happens when you issue no shutdown on dot11radio interface before sub interfaces are configured? | State of the interface changes to reset. |
| What does encapsulation dot1q 50 command do? | Used on a sub interface, tells the AP it will now be accepting traffic on Vlan 50. |
| What does bridge-group 15 command do? | Used on sub interfaces, when same number is used on a wireless and ethernet sub interfaces it will be bridging the two interfaces. |
| What does the guest-mode command do? | Sets the SSID to be broadcasting. |
| How to verify RF power and channel? | show controllers |
| How to see AP associations | SHOW DOT11 ASSociations |
| what is infrastructure-ssid used for? | It is used to instruct a non-root access point/bridge or workgroup bridge radio to associate with this SSID. |
Created by:
Datheral
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