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Final Prep Flashcards

1
Q

How many classes are in classful addressing?

A

There are five classes, A - E.

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2
Q

T/F: We mostly use classless addressing and subnetting now

A

True

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3
Q

T/F: The TTL value increases by one each time a packet passes through a router.

A

False, the TTL value decreases by one each time a packet passes through a router.

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4
Q

What is the first duty of the network layer?

A

Packetizing, that is, encapsulating the payload in a network-layer packet at the source, and decapsulating it at the destination.

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5
Q

Can the network layer alter the content of the packet?

A

Only if it is too large to be sent, and must be fragmented.

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6
Q

Can network packets ever be decapsulated by routers?

A

Only if the packet needs to be fragmented, otherwise, no.

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7
Q

If a packet in the network layer needs to be fragmented, what must happen to each fragment?

A

The header needs to be copied to each fragment.

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8
Q

What is the basic goal of the network layer?

A

The network layer is responsible for routing the packet from its source to its destination, and finding the best possible route.

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9
Q

What is forwarding?

A

Forwarding is a service provided by the network level, where a packet is received by a router from one of its attached networks, and it forwards the packet to another attached network.

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10
Q

How does the network layer handle error checking?

A

Very poorly, most of the time, although checksum may still be useful to prevent header corruption, but not the whole datagram.

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11
Q

How does the network layer handle flow control?

A

Very poorly, as datagrams are sent as soon as the sender is ready, regardless of the receiver.

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12
Q

What’s the difference between datagram and virtual circuit as far as packet switching?

A

In datagram packet switching, it’s connectionless. This means that the network layer treats each packet independently, so they have no relationships to each other. This means the packets may or may not take the same paths, or arrive in the correct order. Their source and destination are contained in their headers.This is what routers do.

In Virtual-Circuit packet switching, it’s connection-oriented. The packets are all related. A connection is set up, packets all follow the same path, and each has a flow label in the header to guide them. This has the basic setup/transmit/teardown as a normal virtual circuit approach.

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13
Q

Why is virtual circuit beneficial, and why isn’t it used as much these days?

A

Benefits are that the packets are delivered in the same order, the packets don’t need to store the full address of the destination, the connection is reliable

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14
Q

What are the four types of delay?

A

Transmission Delay
Propagation Delay
Processing Delay
Queuing Delay

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15
Q

What is transmission delay?

A

Transmission delay is the amount of time it takes for the sender to line up the bits to send.

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16
Q

What is propagation delay?

A

Propagation delay is the amount of time it takes for a bit to travel from point A to point B through the transmission media.

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17
Q

What is processing delay?

A

Processing delay is the amount of time it takes for a router or a destination host to receive a packet from its input port, remove the header, perform an error detection procedure, and deliver the packet to the output port.

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18
Q

What is queuing delay?

A

Queuing delay is the amount of time a packet waits in the input and output queue of the router.

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19
Q

What is throughput?

A

Throughput is the number of bits passing through a point in a second, which is also the transmission rate. The average speed is determined by the lowest speed segment, or bottleneck/

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20
Q

How does packet loss happens?

A

Packet loss happens when the input buffer of a router fills up, and incoming packets are dropped.

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21
Q

What are the two main causes of congestion?

A

Throughput and delay.

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22
Q

Does discarding packets alleviate network congestion?

A

No, because dropped packets are almost always retransmitted.

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23
Q

What are the two forms of congestion control?

A

Open-loop congestion control and closed-loop congestion control.

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24
Q

What is open-loop congestion control?

A

In open-loop congestion control, policies are applied before congestion occurs.Things like good re-transmission policies, Selective Repeat (where only corrupted/lost packets are retransmitted), acknowledgement policies, discarding and admission policies.

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25
What is closed-loop congestion control?
Closed-loop congestion control happens after congestion has occurred, and there are several methods used: Backpressure, choke packets, impicit signaling, and explicit signaling.
26
What is backpressure?
Backpressure occurs when a node in a network stops receiving data from the immediate upstream node, which congests those nodes, which then stop receiving packets. This can only work with a virtual circuit, as it requires a circuit to work.
27
What is a choke packet?
A choke packet is a packet sent from the router back to the originating sender to inform the sender of congestion.
28
What is implicit signaling?
Implicit signaling is where there is no communication between the congested node(s) and the sender; instead, the sender looks for signs of congestion elsewhere.
29
What is explicit signaling?
Explicit signaling is basically the choke-packet technique.
30
What is an address space?
An address space is the total number of addresses used by a protocol.
31
How many notations are there to represent an IPv4 address, and what are they?
There are three, and they are binary notation (base 2), dotted-decimal notation (base 256), and hexadecimal notation (base 16).
32
What does hierarchical addressing?
This refers to the idea that there is an "order of magnitute" to an address, in that a country contains a state, state contains city, and so on.
33
How is an IPv4 address hierarchical?
The IPv4 address is divided into two part, the prefix, which defines the network, and suffix, which defines the node.
34
What is classful addressing?
Classful addressing refers to when IPv4 addresses had three fixed-length prefixes, A (8), B (16), & C (24). There's still a class D & E, but they're not divided into prefix and suffix, and are reserved.
35
What is address depletion, and how does it relate to classful addressing?
Address depletion refers to the complexity in assigning addresses with classful addressing, as a type A address can only be given to 128 addresses, but each one needs about 16 million nodes.This is rare, so most of the addresses go unused.
36
How large is the subnet for the following prefix lengths? 8 16 24
8 - 128 16 - 16,384 24 - 65,536
37
What is subnetting?
In subnetting, a class A or class B block is divided into several subnets to break it up.
38
What is supernetting?
In supernetting, several Class C blocks are combined into one.
39
What is classless addressing?
In classless addressing, there are variable-length blocks that do not belong to any classes.The size of the network is inversely related to the length of the prefix.
40
What is route aggregation?
Route aggregation occurs when blocks of addresses are combined to create a larger block, allowing routing to be done based on the prefix of the larger block.
41
What is hierarchical routing, and how is it applied?
Hierarchical routing is a method developed to handle the issue of gigantic forwarding tables, allowing tables to be broken down into sub-tables, locally.
42
What is unicasting?
Unicasting is when there is one source, and one destination network. One sender, one recipient.
43
What is multicasting?
In mulicasting, there is one source and multiple recipient (although not necessarily all possible recipients). Multicasting is more efficient than unicasting.
44
How many methods are there for representing addresses in IPv6? What are they?
There are two, Binary and Colon Hexidecimal.
45
What is colon hexidecimal?
Colon hexidecimal is one of two methods for representing addresses in IPv6, using groupings of four hexidecimal digits separated by a colon, eight in all.
46
What is mixed notation in regards to IPv6?
Mixed notation occurs when dotted-decimal notation is used within IPv6 notation. This occurs in translating an IPv4 address into IPv6.
47
How large is the address space of IPv6?
The address space of IPv6 is 2^128. This renders address depletion functionally impossible.
48
How many address types are there in IPv6, and what are they?
There are three address types in IPv6, Unicast, Anycast, and Multicast.
49
What is an anycast address?
An anycast address is an address that defines a group of computers that all share a single address. The packet in question is delivered to the "most reachable" member of the group.
50
What are the names of the fields in the IPv4 datagram header?
``` Version Number Header Length Service Type Total Length Identification, Flags, and Fragmentation Offset Time-to-Live Protocol Header Checksum Source and Destination Address Options Payload ```
51
What are the three parts addresses in the global unicast address block are divided into?
Global routing prefix, subnet identifier, and interface identifier.
52
What is a compatible address?
A compatible address is an address where the first 96 bits are zero, followed by 32 bits of IPv4 address.
53
What is a mapped address?
A mapped address is what's used when a computer already migrated to IPv6 wants to send a message to a computer still using v4.
54
What is autoconfiguration?
Autoconfiguration is a function of IPv6, whereupon a host can use DHCP to configure its own IPv6 address.
55
What is renumbering?
Renumbering is a functionality built-in to IPv6 that allows for the renaming of the address prefix, in order to allow sites to change service providers.
56
How is fragmentation handled differently in IPv6 compared to IPv4?
Packets can only be fragmented by the source, not by routers. This speeds up processing at routers.
57
What are the strategies for transition from IPv4 to IPv6?
Dual stack, tunneling, and header translation.
58
What is the dual-stack transition strategy?
In this strategy, all hosts should run both IPv4 and IPv6 until they are fully migrated to IPv6.
59
What is the tunneling transition strategy?
The tunneling transition strategy is used when two IPv6 machines need to run through an IPv4 section to communicate. In this situation, the IPv6 packet is encapsulated in an IPv4 packet on entering the region, and decapsulated when leaving.
60
What is the header transition strategy?
This transition strategy is used when the majority of the internet is using IPv6. If the sender is sending IPv6 to something that only understands IPv4, the header of the packet will have to be completely translated.
61
What is the first duty of a transport-layer protocol?
The first duty of a transport-layer protocol is to provide process to process communication.
62
What is an ephemeral port number?
An ephemeral port number is a port number a client program assigns itself.
63
What are the three ranges of port numbers?
Well-known (assigned and controlled by ICANN), registered (can be registered with ICANN to prevent duplication), and dynamic (cannot be registered, used as temporary port numbers).
64
What is a socket address?
A socket address is a combination of an IP address and a port number.
65
How does a connectionless service work?
A connectionless service divides its message into chunks of data of the size acceptable by the transport layer and deliver them there one by one. These chunks are then transported, without any relation being made between them.
66
How does a connection-oriented service work?
A connection-oriented service first establishes a logical connection between itself and the server. Then it transmits, and tears down the connection.
67
What is the Go-Back-N Protocol?
In Go-Back-N, multiple packets are sent while awaiting acknowledgement, and copies of those sent packets are kept until their acknowledgement is received.
68
What is the selective-repeat protocol?
The selective-repeat protocol only resents packets that have actually been corrupted or lost.
69
What port is HTTP on?
80
70
What is a user datagram?
A user datagram is a form of UDP packet, which has a fixed-size header of 8 bytes made of four fields, each of two bytes.
71
What are the header fields of a user datagram?
Source port number Destination port number Total length Checksum
72
Even though UDP has nearly none of the requirements for a reliable transport-layer protocol, why is it still preferred for some applications, and what are they?
Since UDP is connectionless, each packet is independent from the next, making it faster for sending short, quick messages. In addition, lack of error-correction means that the transmission isn't interrupted for error-correction, allowing things like streaming to happen uninterrupted. Finally, its lack of retransmission means it won't clutter up error-prone media.
73
What is TCP?
TCP, or transmission control protocol, is a reliable, connection-oriented transport-layer protocol.
74
What are groupings of bytes in TCP called?
Segments.
75
What are the fields of a TCP segment?
There are two: sequence number, and acknowledgement number.
76
What is a sequence number?
A sequence number is a random number added to the front of the foremost segment, and then added to the front of each following segment, incremented by the number of bytes in the previous segment.
77
What are the header fields of a segment?
``` Source port address Destination port address Sequence number Acknowledgement number Header length Control Window size Checksum Urgent pointer Options ```
78
What are the steps in a 3-Way TCP Handshake?
The client sends a SYN segment with only the SYN segment set, and allows for the synchronization of sequence numbers, the Initial Sequence Number (ISN). The server sends a second segment, SYN + ACK. This synchs comms for the other direction, and acknowledges the message sent by the client. The client sends the third segment, with just an ACK.
79
What is half-close in regards to TCP?
Half-close refers to the ability in TCP for one side of the connection to stop sending data while still receiving data. It'd be used in situations like downloading large files.
80
What is the difference between ACK and SACK?
look dis shit up yo
81
What is a congestion window?
Normally, the size of the send window of the sender is determined by the receiver, which keeps things from getting crazy. But! Routers have buffers, and can get congested. To prevent this, the congestion window comes into play. It's lowered in size as congestion is detected, keeping congestion out.
82
The performance of a network can be measured in terms of _____.
Delay, throughput, and packet loss.
83
An IPv4 address is a _____ bit address that uniquely defines a host on the Internet.
32
84
What are private IP addresses for, and how are they used?
Private IP addresses allow for the prevention of address depletion, and allow internal networks to configure themselves internally and privately without worry.
85
What is the a short-term solution to IPv4 running out of addresses?
Use classless addressing to allow better distribution of addresses, or use NAT to allow multiple hosts on private addresses to use a single public address.
86
What is address aggregation?
See supernetwork, combining a number of Class C subdomains.
87
What does APIPA stand for, and what is it used for?
Automatic Private IP Addressing, allows for self-configuration of IP addresses when DHCP isn't available. On windows.
88
What address is used for loopback? What is the purpose of the loopback address?
127.0.0.1, and it allows users to access their own network port.
89
What is CIDR notation?
Classless Inter-Domain Routing, look dis up
90
What is multicast? What is it used for?
In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source. Copies are automatically created in other network elements, such as routers, but only when the topology of the network requires it. 224.0.0.0 through 239.255.255.255
91
Are IP broadcasts forwarded by routers?
They are not.
92
How can an IPv6 device generate a unique address for itself?
It generates its own address from its own 64-bit interface identifier, then checks for neighbors with the same address.

Networking (15 decks)

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