Karteikarten
System Admin- Wireless Networking
Karten in diesem Stapel (21)
- 1Q1: What is meant by the terms a) Frequency b) Wavelength as applied to electromagnetic waves How are they related?a) frequency of a wave is the number of times per second the amplitude of the waves electrical (or magnetic) field goes from max to min back to maximum. The unit of frequency is Hertz (Hz). A frequency of 1 Hz means that the amplitude varies from max to min to max only once per second.
b) Wavelength of a wave is the distance over which the wave must travel for the amplitude of its electrical (or magnetic) field to go from max to min back to max. A wavelength of 1m means that the wave must travel a whole metre before the amplitude has varied through the cycle max-min-max.
The frequency of a wave is related to the wavelength of the wave
v=fλ, where v is the velocity of the wave.
V=velocity (speed at which wave travels)
f= Frequency and λ= Wavelength - 2Q2: Info (data) is carried by a carrier wave by changing one of its properties . What is meant by the term "carrier wave" ? Hence draw diagrams showing a) amplitude modulation b) frequency modulation of a carrier wave to transfer data?A Carrier Wave is the initial electromagnetic wave, eg the radio wave or the light wave
- 3a) amplitude modulation
- 4b) Frequency modulation
- 5Q3: what is meant by the term bandwidth and on what does it depend?is the range of frequencies occupied by a modulated wave. Its size depends on the type and ‘depth’ of the modulation.
- 6Q4: Compare and contrast the different types of contrast links?
- 7Q5: what are the characteristics of a wireless PAN network?A Wireless PAN network centres around an individual, connecting their devices wirelessly together. Technologies that are use in Wireless PANs include:
• Bluetooth (radio)
• IrDA (Infrared light)
• Wireless USB (radio)
• Zigbee (radio)
• Wi-Fi (radio) - 8Q6: what are the requirements for a mesh network?A wireless mesh network is created when a network has:
• Ad hoc capabilities at the physical layer: all devices can communicate directly to any other device within radio range, and
• Mesh routing capabilities at the network layer: nodes can act as a router and forward packets on behalf of another node, thus providing multi-hop capabilities to the network. Routes are created dynamically, to cope with devices entering and leaving the network, or moving around.
Wireless mesh networks do not require infrastructure such as access points to operate, although they may have a connection to a fixed network such as the internet. - 9Q7: what are the key components of a Wireless LAN and what does each component do?Key components of a WLAN are:
• Wireless Access Point (AP):
The base-station for the network. They normally act as routers and as connections to a fixed-wire network. They will have a wireless network interface for clients but may also be able to accept fixed-wire connections.
• Wireless client:
Device with a wireless network interface. This may be the only network interface on the client, or it may be one of several, which may include a fixed wire interface. Thus clients can be mobile devices such as smartphones and tablets, or static devices such as desktops. - 10Q8: What are, and what are the differences between BSSID and a SSID?A BSSID is the Basic Service Set Identifier. It is the MAC address of the Access Point.
A SSID is an ‘informal’ name for a BSS, and can be chosen by the AP administrator. - 11Q9: What are, and what are the relationship between BSS and an ESS?A BSS is a Basic Service Set – an Access Point and its connected devices
A ESS is an Extended Service Set. An ESS is a set of connected BSSs that share the same SSID, security and back-end wired network (distribution system). A device sees all APs in a ESS as single BSS. - 12Q10: What is the difference between ad hoc and infrastructure mode in wireless?In ad hoc mode there is no access point and devices communicate directly with each other. The SSID of the network is chosen by the client that ‘starts’ the network and it is broadcast in turn by a randomly chosen member of the network.
In Infrastructure mode devices are all clients, which then connect to dedicated Access Points. - 13Q11: You are in a car that is driving through a town centre and you are maintaining your laptop’s wireless connectivity as you go by attaching to different wireless networks. What type of roaming are you doing, and what do you need in order for it to be successful?External roaming. You need to have software installed on your laptop to maintain the session as you move from one network to another.
- 14Q12: Your wireless router is operating on channel 1. Your neighbour’s wireless router (just the other side of the wall from yours) is also operating on channel 1. What impact might this have on the performance of both wireless networks, and what can you do about it?Both networks will suffer from interference which will result in a loss of performance (reduced data rates) possibly down to no connectivity at all.
You (or your neighbour) should change channels, to one that does not overlap, ie to channel 6, or above (assuming not other APs are around). - 15Q13: Why is physical layer security important on a wireless network?Wireless is an open medium so anyone can capture data packets, unlike a wired network where some effort has to be made to tap the cable.
- 16Q14: What encryption and integrity protocols were used with WEP and why are these a problem in modern networks?The protocols are RC4 and CRC-32
- 17Q14: continued RC4RC4 was used for encryption. It is a stream cipher, and so security is only ensured if the generated keystream is not re-used. In WEP the key used to generate the keystream can itself be weak (because the WEP key is chosen by the user) and the key for the keystream is generated by simply ‘adding’ a random number (initialisation vector) to the front of the WEP key, which is mathematically weak. The IV is only 24 bits so there are not many variations, which matters because wireless networks – where packets are frequently lost – and stream ciphers are not a good combination as lost packets break the keystream sequencing. Therefore the developers decided to generate a new key, and therefore keystream, for every packet sent: on a busy network it takes only minutes to use all possible keystreams so they have to be re-used – a serious weakness in security terms.
- 18Q14: continued CRC-32CRC32 was used for integrity. It is not a cryptographic integrity algorithm and so has ‘collisions’ – different inputs give the same output. Thus an attacker can selectively modify the data in the packet without changing the output of the CRC32 algorithm in order to obtain information that will allow them to decrypt the packets.
- 19Q15: What is the relationship between WEP, WPA and WPA2?WPA was a half-way house between WEP and WPA2. It solved the major problems of WEP by replacing the very simple keystream key generation (secret key + IV) by the Temporal Key Integrity Protocol (TKIP).
• TKIP takes the secret key, the initialisation vector, a sequence counter and the MAC address of the sender and mixes them altogether to generate an encryption key AND an integrity key for each packet sent. The mixing process ensures much greater uniqueness of keys.
• TKIP is also able to rekey, that is change the keys used in an ongoing communication session.
• TKIP uses a Message Identity Check algorithm, called Michael, with the new integrity key.
Therefore, even though the use of legacy hardware requires that RC4 and CRC-32 are still being employed, compared to WEP, if WPA is used:
• The use of key mixing (and rekeying if used) means that decoding data is much more complex because much less data is encrypted using the same key;
• The use of Michael prevents modified packets being accepted. (Michael acts as a check on packets that CRC-32 has accepted) - 20Q15: WPA2WPA2 implements the mandatory requirements of the current security standard for WLANs. Only WLAN devices that support WPA2 are able to use the Wi-Fi trademark. Its key features are:
• RC4 is replaced by a secure block cipher called AES (Advanced Encryption Standard)
• The mode of the AES used in WLANs incorporates authentication of the packets, thus confirming the identity of their sender as well as the integrity of the packets themselves.
• It provides for two different methods of establishing the secret key:
o Personal mode – Access Point and all connected computers use the same secret key, chosen by the AP administrator
o Enterprise mode – a back-end server provides a unique key for each computer that connects to an AP and group keys for any broadcasting. The keys are chosen by the system, not by a human administrator. - 21Q16: Why was wi-fi protected setup introduced and how has it introduced a weakness into WPA2 security?16. Wi-Fi Protected Setup was developed to enable users with little or no technical knowledge to setup wireless communications using WPA or WPA2 with a secure pre-shared key (secret).
Although intended to make life easier, and more secure, for WLAN users, in fact the PIN method (which is mandatory in WPA2 for both clients and access points) introduced a flaw in security which was identified in December 2011. Because the PIN is effectively only 7 digits long it can be subjected to a brute-force attack in which all possible PINs can practically be tried, which, when the attacker finds the correct one, allows them to connect to the access point and then obtain the pre-shared key.
Some access points prevent such an attack by slowing or disabling the PIN method after a specified number of failed connection attempts. Some access points allow the PIN method to be disabled. Others appear to allow it but do not do it, and others don’t allow it to be disabled at all.
Informationen
- Beschreibung
- Karteikarten am System Admin- Wireless Networking, erstellt von Robena786 am 22/05/2015.
- Erstellt von
- Robena786
- Aufrufe
- 2
- Bewertung