Final Flashcards
1
Q
What is an important function of a router?
A
Path Determination
2
Q
How does a router accomplish path of determination?
A
Routing table
3
Q
How are routing tables built?
A
Routing protocols
Routing algorithms
4
Q
Why do we need dynamic routing (auto) algorithms?
A
- Topologies can change
- Link costs can change
- Nodes and links can fail
5
Q
What are the two broad types of dynamic routing algorithms?
A
- Distance vector (DV)
- Link state (LS)
6
Q
What is the basic strategy for DV?
A
- If a router receives an update about an unknown network, it accepts the update.
- If a router gets a better update about a known network, it accepts the update. (modifies the the table)
7
Q
What is the updated DV algo to detect faults?
A
- If a router receives an update about an unknown network, it accepts the update.
- If a router gets a better update about a known network, it accepts the update.
- If the update isn’t better than existing entry - don’t accept the new update.
8
Q
What is the classic problem in DV?
A
Count to infinity
9
Q
Summarize the count to infinity problem?
A
- Detects a fault
- Set the distance to infinity
- Then propagates this reading to other routers
- Then all the other routers ‘spinning’ in infinity
10
Q
What are the three solutions to the count to infinity problem?
A
- Sol 1: Set a max number to infinity (e.g. 16)
- Sol 2: Split horizon (prevent neighbours from sending info of a router that they are not directly connected to)
- Sol 3: Hold-down timer: temporary timer until the network stabilizes OR until you start updating the DV tables again.
11
Q
What are the two important concepts of the link state dynamic routing algorithm?
A
- Send (original) information to all nodes, not just neighbours.
- Send information about directly connected links only, not the entire table.
12
Q
What are the main characteristics of the link state algorithm?
A
- Link state packet (LSP) sent to directly connected nodes
- LSPs are forwarded to every node on the network
- Each router builds a link state DB with the LSPs which is a topology or graph of the entire network
- From this DB routers can calculate the shortest path
13
Q
What are the components of the LSP?
A
- RouterID
- Link state (x’s neighbours & costs)
- Sequence number (first LSP has seq=0 and goes seq++)
- Age (Set to max when LSP is created and decrements at every hop until discarded when age=0)
14
Q
Why LSP uses a sequence number?
A
Tells router which LSP is more recent.
15
Q
Why LSP uses age?
A
Prevent unnecessary floodings, LSPs are not forwarded unless they contain new information. However, flooding is needing sometimes to flush the shit out.
16
Q
What is the flow chart for an LSP?
A
- Receive LSP of X
- Is there an LSP of X in the DB (yes –> is it new? no –> discard it)
- Accept LSP decrement age
- Send on outlines
- Re-run shortest path algorithm
17
Q
What are the border gateway protocol principles?
A
- Path Vector Routing
- Path Vector Messayges
- Policy Routing
- Path Attributes
- TCP Connection
18
Q
What is ICANN?
A
Internet Corporation for Assigned Numbers and Names
19
Q
When was the last IP address assigned?
A
Feb. 2011
20
Q
What is subnetting?
A
The process of dividing a network into multiple smaller networks so that each smaller network has its own network address.
21
Q
What is supernetting?
A
Supernetting is the opposite of subnetting, and involves combining smaller networks into one larger network.
22
Q
What is VSLM? Why is it used?
A
Variable length subnet masking. It is used to prevent the waste of IP addresses in basic subnetting.
23
Q
What are some issues with basic subnetting?
A
You waste a lot of addresses, because they get equal chunks of IP address.
24
Q
What are the rules to create a supernet?
A
- The number of blocks must be a power of 2
- The block addresses must be contiguous
- The third byte of the first address block must be evenly divisible by the number of blocks.
25
What is supernetting?
Supernetting is the opposite of subnetting, and involves combining smaller networks into one larger network.
26
How is IPv6 better than IPv4?
- Better utilization of addresses (no classes)
- Support for resource utilization
- Support for security
27
What are some issues with basic subnetting?
You waste a lot of addresses, because they get equal chunks of IP address.
28
What are the rules to create a supernet?
1. The number of blocks must be a power of 2
2. The block addresses must be contiguous
3. The third byte of the first address block must be evenly divisible by the number of blocks.
29
What is the size of an IPv6 address?
128 bits
30
How is IPv6 better than IPv4?
- Better utilization of addresses (no classes)
- Support for resource utilization
- Support for security
31
What are the rules of simplification of IPv6 addresses?
- Remove leading zeros
| - Consecutive groups of zeros to double colon notation (only once per address)
32
What is a loopback address IPv6?
All 128 bits are 0 except the last bit.
33
What is the unspecified IPv6 address used for?
Finding the devices IP address (RARP).
34
What is an IPv6 multicast address?
Defined a group of hosts.
35
What is an IPv6 mapped address?
8 zero bits - 72 zero bits - 16 one bits - 32 bits (IPv4 address)
36
What are the security goals of ESP (IPv6 Datagrams)?
- Confidentiality
- Integrity
- Authentication
37
What is the unspecified IPv6 address used for?
Finding the devices IP address (RARP).
38
What is an IPv6 multicast address?
Defined a group of hosts.
39
What is ESP?
Encrypted Security Payload
40
What are the security goals of ESP (IPv6 Datagrams)?
- Confidentiality
- Integrity
- Authentication=
41
What are the two modes for ESP deployment?
- Transport mode
| - Tunnel mode
42
What is ESP transport mode?
Encrypting only the payload
43
What is ESP tunnel mode?
Encrypting the payload and the base header
44
What are the three strategies to transition from IPv4 to IPv6?
- Dual stack
- Tunneling (auto or config)
- Header translation
45
What is the frequency of wireless networks?
800KHz to 5GHz
46
What is the WLAN protocol?
IEEE 802.11
47
What are frequencies measured with?
Hertz
48
What is a Hertz?
1 Hertz = 1 cycle per second
49
What is the frequency of wireless networks?
800KHz to 5GHz
50
What is the WLAN protocol?
IEEE 802.11
51
What is WiMAX?
802.20 can operate on the 2, 2.5, 3G
52
What wireless metropolitan?
802.16 Fixed WiMAX
53
What is a passive association (or beaconing) for wireless access points?
- APs can be set to beacon mode, where they periodically send beacon frames with an SSID
- Wireless client in the range can detect the beacon frame
- Clients select one access point with the strongest signal and sends association request
- Selected AP sends association response
54
What is an ESS?
Extended service set, a set of infrastructure BSS
55
What are two significant addresses of an infrastructure BSS?
- BSS ID --> MAC address of the AP serving the BSS
| - ESS ID --> Character string (max 32 bytes) assigned by admin (e.g. the fucking name of the network asshole)
56
What is an active association for wireless access points?
- Client sends a Probe request frame
- All APs within reach respond with a probe response
- Clients select one access point with the strongest signal and sends association request
- Selected AP sends association response
57
What is a passive association (or beaconing) for wireless access points?
- APs can be set to beacon mode, where they periodically send beacon frames with an SSID
- Wireless client in the range can detect the beacon frame
- Clients select one access point with the strongest signal and sends association request
- Selected AP sends association response
58
Which wireless connection methods use SSID?
Active association NOT beaconing
59
What is a problem with CSMA/CA?
Hidden nodes causing frames to collide.
60
What is wireless disassociation?
- If a client or an AP wants to terminate an association, it sends a Dissassociation frame.
61
What is wireless authentication?
- For secure connections in wireless networks using protocols such as WEP and WPA1
- The legit wireless client and AP share a secret key
- Client send auth request
- AP sends a challenge text
- Client encrypts the challenge text with the secret key
- Sends it back to the AP
- AP decrypts it, if it passes then ACK success
- Client sends an association request
- AP responds
62
Can an RTS collide with a CTS in CSMA/CA?
Small probability which is reduced with used two wait times:
- DIFS (distributed interframe space) wait time for RTS (50 microsecs)
- SIFS (Short interframe space): wait time for CTS (10 microseconds)
63
What is a problem with CSMA/CA?
Hidden nodes
64
What is the solution for the hidden nodes problem in CSMA/CA?
Modification to the CSMA/CA protocol:
- Use two control frames
- RTS (request to send)
- CTS (clear to send)
65
What if two RTSs collide in CSMA/CA?
This can happen, but the AP will not send CTS to either station.
66
Can an RTS collide with a CTS in CSMA/CA?
Small probability which is reduced with used two wait times:
- DIFS (distributed interframe space) wait time for RTS (50 microsecs)
- SIFS (Short interframe space): wait time for CTS (10 microseconds)
67
What technology is used for the physical layer for the wireless transmission?
Spread spectrum - key idea is to spread the information signal over a wider bandwidth in order to make jamming or interception more difficult
68
What are the two broad types of spectrum techniques
- Frequency hopping spread spectrum (FHSS)
| - Direct sequence spread spectrum (DSSS)
69
What do FHSS and DSSS use in the physical layer of a wireless network?
Pseudorandom Sequence Number Generator PSNG
70
What is a PSNG?
Uses a specific hardware circuit.
71
What are the characteristics of 1G cellular networks?
- Voice only analog
- Circuit switched
- FDMA
72
What are the characteristics of 2G cellular networks?
- Voice + SMS
- Analog (Voice)
- Digital (SMS)
- Circuit switched
- TDMA
73
What are the characteristics of 2.5G cellular networks?
- Voice + medium speed data
- Digital
- Circuit switching and Packet switching
CDMA
74
What are the characteristics of 3G and 3G+ cellular networks?
- Voice + highspeed data
- Digital
- Packet switching
CDMA
75
What are the characteristics of 4G cellular networks?
- All IP Network
| - Fully packet switched
76
How does the 3G cellular network work?
```
Step 1: USIM (i.e. SIM card) device transmit
Step 2: BTS (Cell tower)
Step 3: RNC (radio network controller)
Wired from now on
Step 4: Mobile switching center
Step 5: Global mobile mobile switching center
Step 6: Router
Step 7: The Internet
```
77
What are the advantages of optical networks?
- Highspeed over long distances without repeaters
- Small size
- Immunity to crosstalk (not interference)
- Longer lifetimes (no corrosive materials)
- More secure (absence of the power dissipation and electromagnetic radiation)
78
What are the characteristics of a first generation optical network?
- Fiber used purely as a transmission medium
- Switching and processing by electronics
- Examples: SONET, FDDI
79
What are the characteristics of a second generation optical network?
- As data rates get higher, more difficult to process data electronically
- Drive to incorporate switching and routing into the optical domain --> Development of All-optical networks.
80
All-optical networks use what type of multiplexing?
Wave division multiplexing (WDM).
Recently, more than 100 channels at 10 Gbps --> 1Tbps per fiber per second
81
What is a step index optical fiber?
Density of core is constant
82
How does an optical cable work?
Optical fibers use total internal reflection to guide the light beam through the core.
83
What is a graded index optical fiber?
Density of core decreases gradually outward.
84
What are modes in optical fiber cables?
Mode refers to the distribution of light energy within the fiber.
Larger the core, more the number of modes and more the attenuation.
85
What is the single mode for optical cables?
Small core diameter: all the signal energy travels in a single mode
86
What is the multiple mode for optical cables?
Large core diameter; light energy propagates in the form of multiple modes.
87
What is wavelength filter in optical cables?
- Device that selects one wavelength and rejects others.
| - Building block for other optical devices
88
What is wavelength multiplexer in optical cables?
- A multiplexer combines signals at different wavelengths on its input ports onto a common output port (a demux performs the opposite function)
89
Describe wavelength router/switch?
- Consists of input and output ports
- Each input port carries a WDM signal consisting of a set of wavelengths
- The router exchanges some wavelengths between inputs and outputs
- There are two types: static and dynamic
90
What is a wavelength add/drop MUX?
- Simple form of router: 1 input and 1 output
| - Has a local port wherein wavelengths are added to or dropped from the incoming light stream
91
What is an optical transmitter?
- Consists of an LED or laser source enclosed within a reflective cavity causes it to oscillate with positive feedback to give amplifications.
92
What is an optical receiver?
- Restores electrical signals from optical data
- Consists of a photodiode (detects optical signals and converts them to electrical signals), a signal conditioner and a signal-to-bit converter.
93
What are broadcast and select on optical networks?
- Each node transmits at a specific wavelength
- A MUX/DEMUX (called coupler) receives signals from the nodes and broadcasts them to all nodes.
- Each node has a tunable optical filter to select the desired wavelength for the reception
