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Systems and Networks > Internetworking > Flashcards

Internetworking Flashcards

1
Q

What are distributed systems?

A

Interconnection of computers across a network to provide a common service or set of services e.g. the internet

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2
Q

What is the client-server model?

A

An application providing a service (server) is contacted by an application that needs to use the service (client)

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3
Q

Name some advantages of a distributed system?

A
  • Access to remote resources
  • Access to computing power that you don’t have locally
  • Scalability
  • Robust (resources duplicated)
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4
Q

In the client-server model, if the web browser you’re using is a client, what is the server?

A

Web server

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5
Q

What are the 3 main times of computer addresses?

A

Hostname address
IP address
Hardware address

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6
Q

What does a hostname address look like?

A

severn.cs.nott.ac.uk

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7
Q

What does an ip address look like?

A

128.243.10.4

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8
Q

What is a hardware address also known as?

A

MAC address, physical address, ethernet address

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9
Q

Do organisations typically use one network technology?

A

No, usually several

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10
Q

What does universal service mean?

A

Any two computers should be able to communicate

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11
Q

What is internetworking?

A

The interconnection of several heterogeneous networks to provide a universal service

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12
Q

What is the universal hardware component used to connect heterogeneous networks?

A

Router

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13
Q

How does internet protocol software provide universal service?

A

By creating a single virtual network

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14
Q

Can a router connect more than 2 networks?

A

Usually yes

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15
Q

When did the internet emerge into public domain and who controls it?

A

1990s
- the IETF, internet engineering task force

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16
Q

What is the layered model?

A

Application
Transport
Internet
Network interface

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17
Q

What is the internet reference model?

A

Application
Transport
Internet
Network Interface
Physical

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18
Q

What does host computer mean in TCP/IP?

A

Any system that connects to the internet and runs applications.

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19
Q

What does IP address stand for?

A

Internet protocol address

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20
Q

Why are there two versions of IP?

A

IPv4 and IPv6 because the internet ran out of address space

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21
Q

Under the IP addressing scheme, each host is assigned a…..

A

Unique binary number
128 bit for IPv6
32 bit for IPv4

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22
Q

What is a 32 bit IP address divided into?

A

Prefix - physical network the host is attached to
Suffix - a host attached to a given physical network

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23
Q

Where are prefixes and suffixes for IP addresses co-ordinated?

A

prefixes - globally
suffixes - locally

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24
Q

What does the size of prefixes and suffixes in an IP address determine?

A

max number of networks and max number of hosts per network

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25
Q

In IPv4 addressing, what do the first four bits of an address determine?

A

Specifies its class and how the remainder is divided into prefix and suffix

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26
Q

Who assigns IP numbers?

A

Public internet network numbers are assigned by Internet service providers (ISPs) and then co-ordinated by ICANN (Internet corporation for assigned names and numbers)

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27
Q

What is the difference between subnet addressing and classless addressing?

A

Subnet addressing was originally just used in large organisations that connected to the internet, classless addressing extends this approach to the entire internet

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28
Q

What is the idea between IPv4 subnet and classless addressing?

A

Allows the division between the prefix and the suffix to be at an arbitrary boundary

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29
Q

Which version of IP were subnet and classless addressing developed for/in?

A

IPv4

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30
Q

What is the motivation behind arbitrary boundaries in IP addressing?

A

The smallest class of address uses 8 bit suffixes but many networks may only need 3,4,5,6,7 bits for the suffix so are wasting part of the address

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31
Q

What are address masks?

A

They are used to identify the network prefix / prefix/suffix boundary

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32
Q

What is classless addressing also known as?

A

CIDR: classless inter-domain routing

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33
Q

What does the special IPv4 address all-0s mean?

A

this computer

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34
Q

What does the special IPv4 address all-1s mean?

A

A limited broadcast on local network

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35
Q

What does the special IPv4 address with a network prefix and all 0s suffix means?

A

identifies the network

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36
Q

What is an all 0s IPv4 address used for?

A

Used during bootstrap

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37
Q

What types of devices are always given two or more IP addresses?

A

Routers and multi-homed computers

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38
Q

What are multihomed hosts good for?

A

Increasing performance, connecting to multiple network

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39
Q

What is the more compact address form used for IPv6?

A

colon hexadecimal

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40
Q

Name the 3 types of special IPv6 addresses?

A

Unicast, multicast, anycast

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41
Q

What is the purpose of a unicast IPv6 address?

A

Corresponds to a single computer and any datagrams are routed along the shortest path to it

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42
Q

What is the purpose of a multicast address in IPv6?

A

Address corresponds to a set of computers and membership to this set can change at any time, a copy of any data is routed to all members

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43
Q

What is the purpose of an anycast IPv6 address?

A

Corresponds to a set of several computers with the same prefix, a datagram sent to the address is delivered to exactly one of the computers (closest to sender)

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44
Q

What is a datagram?

A

a universal virtual packet defined by an internet protocol

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45
Q

How does the size of IPv4 and v6 datagrams differ?

A

v4 - 64k octets including header
v6 - 64k octets PLUS header

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46
Q

What does a router use to forward an IP virtual packet?

A

uses a local forwarding table

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47
Q

What does a local forwarding table contain?

A

Entries of networks with address, mask, next hop

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48
Q

What does longest prefix match mean?

A

If a table has both
128.10.0.0/16
128.10.2.0/24
and a datagram arrives for
128.10.2.3
it matches both the first sections but will use longest prefix match and go for 128.10.1.0/24

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48
Q

What situations do IPv4 and IPv6 not guarantee to deal with?

A
  • datagram duplication
  • delayed or out of order delivery
  • corruption of data
  • datagram loss
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49
Q

What is encapsulation?

A

An IP datagram sent over a physical network is placed in the data area of a frame and the frame type is set to IP

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50
Q

What is MTU?

A

Maximum transmission unit - max of data that a frame can carry on a given network

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51
Q

If a packet encounters different MTU sizes as it travels, what happens to the datagram?

A

It is fragmented

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52
Q

What is IPv4 fragmentation?

A

An IPv4 datagram larger than MTU is split into smaller datagrams, not all of equal size

53
Q

How does IPv6 fragmentation work?

A

Datagram has an unfragmentable part so fragmentable part is split up and unfragmentable part is attached to all subdivisions.

54
Q

How is fragment size controlled in IPv6?

A

Fragment is chosen to be MTU of network at source and if a router gets a datagram bigger than MTU it sends an error message and doesn’t store or transmit

55
Q

What do Path MTU and Path MTU discovery mean?

A

Path MTU - minimum MTU along a path
Path MTU Discovery - process of learning path MTU

56
Q

What is the process of path MTU discovery?

A

iterative process of trying a size and seeing if an error gets returned

57
Q

How does fragmentation reassembly work?

A

Done at final host (fragments can take separate routes), headers indicate when data is a fragment and then where it goes

58
Q

How are fragments identified when they don’t always arrive at the destination together or in order?

A

An identification field determines with datagram the fragment belonged to
A fragment offset field determines where in the original datagram the payload of a fragment goes

59
Q

What does a receiver do when it receives a fragment?

A

Starts a timer, if timer expires before all fragments are received it discards them all, fragments are buffered in memory until this point

60
Q

Why should fragmentation generally be avoided?

A

On a lossy network, a fragmented datagram is more likely to be lost

61
Q

How does MTU size affect network design?

A

A network shouldn’t be designed to involve a sequence of decreasing MTUs

62
Q

What does ARP stand for?

A

Address resolution protocol

63
Q

What does ICMP stand for?

A

Internet control message protocol

64
Q

What does DHCP stand for?

A

Dyanamic host configuration protocol

65
Q

What does NAT stand for?

A

Network Address translation

66
Q

Are IP addresses hardware dependent or independent?

A

Independent!

67
Q

At way layer are IP addresses mapped to hardware addresses?

A

Link layer, address resolution protocol (ARP) is used on ethernet

68
Q

What is mapping between IP adresses and mac addresses known as? When is it done?

A

Address resolution, done when computers are on the same physical network

69
Q

What does ARP do?

A

Translates between IPv4 addresses and hardware addresses

70
Q

What will a sender use ARP (address resolution protocol) for?

A

Finding the hardware address of a destination on the same network or a next-hop router if on another network

71
Q

What is an IPv4 ARP discovery packet?

A

A packet sent from a host to all other hosts, but only the one with that IP address responds and then the sending host updates it’s ARP cache

72
Q

What does the ARP cache of a host store?

A

Mappings of IP to hardware addresses, when it runs out of room the oldest mapping is removed

73
Q

When is an ARP request sent?

A

When the host has a datagram to deliver to that address

74
Q

Does IPv6 use ARP?

A

No, it uses neighbour discovery (IPv6-ND)

75
Q

How does IPv6-ND work?

A
  • IPv6 defines a multicast address for all nodes listening
  • requestor multicasts and asks neighbours to reply
  • records addresses in table in cahce
  • contacts neighbours periodically to check they are still active
76
Q

What are the two types of messages in ICMP?

A
  • to report errors
  • to obtain information
77
Q

Using ICMP, what does a router do when it detects a packet is in the wrong place?

A

Sends an ICMP redirect packet to sender to inform it
- sender can update tables

78
Q

What’s wrong with ICMP redirects?

A
  • not trustworthy
  • can be used to tamper with routing tables
  • most dedicated routers are set to ignore them
79
Q

What information does a router need on boot up that is provided by the system administrator?

A

IP address for each network connection
Protocol software to run
Initial values for a routing table

80
Q

What does a device do when plugged into a network?

A

Obtains an IP address, sets up default route, connects to a DNS server

81
Q

What does DCHP allow clients to do?

A

‘lease’ network and administrative parameters from a central DCHP server
- e.g. IP addresses, gateways/default routes, proxy servers

82
Q

Does a DCHP server need to be on the same network as the host?

A

No, can run via a DCHP relay

83
Q

How does DCHP optimise loss recovery?

A

DCHP ensures missing packets don’t cause misconfiguration - host resending requests or ignoring duplicate requests

84
Q

What does an IPv6 node do that is unique to v6?

A

generates its own IP address

85
Q

How does an IPv6 node generate its own IP address?

A
  • finds network prefix via a mutlicast to all nodes
  • generates a unique suffix (its MAC address)
86
Q

What is it called when IPv6 nodes generate their own IP address?

A

Autoconfiguration

87
Q

Where are private addresses used?

A

internally by a site and never shown to the internet

88
Q

What does a border router do?

A

translates between a sites private address and the address space assigned by their ISP

89
Q

What does NAT do on a border router?

A

Intercepts packets on their way to the internet, addressed with internal addresses and replaces their source addresses

90
Q

What is the advantage when a site uses private addressing and a NAT border router?

A

One single external address can be shared by many computers

91
Q

What does the basic layer of NAT not handle?

A
  • two hosts attempting to communicate with the same external server
  • two or more applications on a given host site attempt simultaneous interaction with different internet destinations
92
Q

What is NAPT? How does it differ from NAT?

A

Transport layer NAT, it allows a site to have an arbitrary number of applications running on arbitrary hosts all communicating with any internet destinations

93
Q

What does NAPT (transport layer NAT) use to distinguish amongst services?

A

Protocol port numbers

94
Q

Where is the transport later?

A

Layer 4 - above IP

95
Q

What two protocols are in the transport layer?

A

UDP and TCP

96
Q

What does UDP stand for?

A

User Datagram Protocol

97
Q

What does TCP stand for?

A

Transport control protocol

98
Q

What can IP NOT distinguish between?

A

Multiple applications on the same host

99
Q

UDP and TCP are known as ‘_____to_____’ protocols

A

end to end

100
Q

What does IP (layer 3) consider as the endpoint of communication, how does this differ with layer 4?

A

IP considers the computer the endpoint but layer 4 is able to have an individual application on a computer as the endpoint

101
Q

Name some features of the UDP (user datagram protocol).

A
  • end to end
  • connectionless
  • message orientated
  • best effort
  • operating system independent
102
Q

UDP is _____ orientated.

A

message

103
Q

What does it mean for an application using UDP that UDP is connectionless?

A
  • no need to establish a connection before sending data
  • don’t need to inform network when finished
  • can generate/send data any time
  • can delay as long as liked between messages
104
Q

What else does UDP send besides the actual data message?

A

Nothing! no extra control messages

105
Q

How does UDP package data?

A

data sent is packaged in one single message, never split or combined, application must send data that will fit into 1 packet

106
Q

UDP uses the same best effort delivery method as IP, what problems can this cause?

A

messages
- lost
- duplicated
- delayed
- delivered out of order
- corrupted

107
Q

What are the four types of interaction that UDP allows for?

A

1-1
1-many
many-1
many-many

108
Q

What identifiers does UDP define?

A

protocol port numbers

109
Q

UDP identifies programs with port numbers, what must an individual computer do with these?

A

Map them to the program identifiers that the operating system uses

110
Q

What does a UDP header include?

A

just protocol port numbers

111
Q

What is a UDP datagram sent within?

A

An IP datagram across the internet

112
Q

TCP is a ‘_____to_____’ protocol

A

end-to-end

113
Q

UDP is message orientated, TCP is _______ orientated?

A

connection

114
Q

What are are TCP connections called?

A

Virtual connections

115
Q

Why are TCP connections called virtual connections?

A

The connections are provided by software

116
Q

What are the two special control messages used by TCP?

A

Synchronisation segment, SYN
Finish segment, FIN

117
Q

TCP requires a startup 3-way handshake, what is sent during this?

A

each side sends a control message with buffer size and sequence number

118
Q

How do transport protocols deal with duplicates and out-of-order delivery?

A

Each packet has a sequence number and packets are stored and delivered in sequence at each layer

119
Q

What is a common approach to handling lost packets?

A

Positive acknowledgment with retransmission

120
Q

What is adaptive retransmission?

A

The timer for retransmission is adapted based on connection delay

121
Q

Sometimes packet sequence numbers in transport protocols may be confused with sequence numbers from a previous session when packet is delayed a long time, how is this resolved?

A

Packets can be given a session identifier

122
Q

Name two methods of flow control for transport protocols.

A

stop and go, sliding window

123
Q

Why is stop and go an inefficient method of flow control?

A

waste of bandwidth if delay is long

124
Q

What are sliding window protocols?

A

a flow control technique where several packets are sent before waiting for acknowledgement on each, amount depends on an agreed window size

125
Q

Where in the internet does congestion usually occur?

A

in routers

126
Q

How does TCP deal with congestion?

A

Rate control - reducing window size

127
Q

What does TCP do after its first lost message in a connection?

A

backs off and sends a small message

128
Q

What is a slow start in the context of TCP?

A

TCP starts a connection with a very small message
- doubles amount of data for every ACK until half window size and then slows increase rate

129
Q
A

Systems and Networks (4 decks)

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