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A Level AQA Computer Science > IP Addresses > Flashcards

IP Addresses Flashcards

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1
Q

What is an IP address

A

A 32 bit long binary number globally unique to each device

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2
Q

How was an IP address made to be user friendly

A

It was split into 4 8 bit chunks with each octet being converted into denary

The 4 values are then written with a dot between them; referred to as dotted decimal notation

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3
Q

What are the initial bits of the IP address referred to as

A

The network id
The initial bits are the same for all devices (hosts) on a particular network.

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4
Q

What are the remaining bits in the IP address referred to as

A

The host id
Used to identify a particular host in that network

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5
Q

What does a router do when it sees an IP packet

A

Examines the network part of address to identify best path forward for the packet

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6
Q

What happens to an IP packet when it arrived at its destination network

A

Host bits are examined to ensure its sent to correct device on the network

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7
Q

What must be true on any network or subnet

A

Network id must be identical for all hosts
Host id must be different
Number of bits allocated to network id is specified by subnet mask

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8
Q

How is a subnet mask written

A

Contains 1s in the position of network id and 0s in position of host id

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9
Q

Examples of how subnet masks are written

A

11111111 11111111 00000000 00000000 OR 255.255.0.0

This means the first 16 bits are the network id

255.192.0.0 means the first 10 bits are network id

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10
Q

What is a newer notation of writing a subnet mask

A

Used a slash and number of bits appended to actual address

E.g. 172.16.200.12/12 means the first 12 bits are the network id

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11
Q

What addresses are reserved on any given network

A

An address with host bits of all 0’s and of all 1’s

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12
Q

What does it mean if the host bits are set to all 0s

A

The address refers to the network itself

Routers use network address to direct packets to a given network

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13
Q

What does it mean for the host bits are all 1s

A

Means its the broadcast address

Needed to send messages to all the devices in a given network

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14
Q

How can you calculate the maximum number of hosts on any network

A

2^n - 2 where n is the number of host bits

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15
Q

Relationship between length of network id and length of host id

A

The greater the length of the network id, the shorter the length of the host id, so a lower number of max hosts can be on a network
E.g.
network id = 24 bits host id = 8 bits
2^8 - 2 = 254

Network id = 12 bits host id = 20 bits
2^20 - 2 = 1,048,574

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16
Q

What is IPv4

A

The IP version which uses 32-bit address structure and has been used for over 4 decades

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17
Q

What is IPv6

A

A newer IP version that allows for a greater amount of addresses

There are 3.4x10^38 possible addresses compared to 4.3x10^9 possible addresses with IPv4

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18
Q

Why was IPv6 developed

A

We were running out of unique addresses so more needed to be made

19
Q

How are IPv6 addresses written

A

Written as 32 hex digits in blocks of 4

E.g.
2001:0db8:0000:0042:0000:8a2e:0370:7334

20
Q

Structure of IPv6

A

Similar to IPv4, initial bits specify network and following specify the host

21
Q

What do IPv6 and IPv4 offer together

A

As both systems can be ran parallel, offers a number of improvements with security

22
Q

What needs to happen for networks to operate efficiently

A

Devices need to be able to determine quickly whether data is to be transmitted to another device on same network or device on a different network

23
Q

What is a subnet mask used for

A

‘Masks out’ host bits of IP address and reveals network to which the device belongs

24
Q

How is ‘ masking out’ performed

A

Carried out by AND operation on IP address and subnet mask

25
Q

Example of bitwise AND result of IP address and subnet mask

A

IP address: 198.35.16.11
Subnet mask 255.255.255.0

10000110 00100011 00010000 00001011
11111111 11111111 11111111 00000000
10000110 00100011 00010000 00000000

198.35.16.0

26
Q

How is the result of a bitwise AND used

A

Used to determine if the destination address is on the same or different network

Use the senders subnet mask on both IP addresses, if results are identical then they’re on the same network if not then they’re on different networks

27
Q

How to identify the network id and host id using subnet mask

A

Subnet mask 255.255.255.0
IP address 198.35.16.11

11111111 11111111 11111111 00000000
<———NETWORK BITS———><—HOST->
10000110 00100011 00010000 00001011

1s correspond to network part of address
0s correspond to host part of address

28
Q

What happens to a message when address is not on same network

A

Message is sent to network’s default gateway. Typically a router that connects local network to internet

29
Q

Why was subnetting created

A
  • Network collisions occurred, resulting in messages being resent
  • bandwidth became congested
  • security issue as shared bandwidth means all network traffic passes every device
30
Q

What is a subnet

A

Subdivisions of a network that are treated logically as separate networks

31
Q

What are subnets connected by

A

Routers

32
Q

What is subnetting

A

Further subdividing the number of available host IDs that they have between individual networks

33
Q

What does subnetting accomplish

A
  • reduces broadcast domain, improving security
  • reduces data collisions
34
Q

What IP address ranges are considered private(non-routable)

A
  • 10.0.0.1 - 10.255.255.255
  • 172.16.0.1 - 172.31.255.255
  • 192.168.0.1 - 192.168.255.255
35
Q

Where are non-routable IP’s reserved for use

A

Within LANs or private WANs

Reduces need for every computer to have its own unique public address

36
Q

Purpose of NAT

A

To allow devices with private IP addresses to communicate outside network via sharing a public IP address provided by NAT

37
Q

Process of NAT

A

Any packet with a private IP address as source address has swapped it for a public address which is routable over the internet.

38
Q

What does DHCP do

A

Dynamically assigns private IP addresses and other config options to devices in a network

39
Q

1st stage of the DHCP procedure

A

Discover - on start up, broadcasts a discover message for DHCP servers

40
Q

2nd stage of DHCP procedure

A

Offer - when DHCP receives request, reserves an IP address for client and sends offer message to client.

Message contains IP address offered, subnet mask, lease duration, IP address of DHCP making offer

41
Q

3rd stage of DHCP procedure

A

Request - in response to DHCP offer, client broadcasts a request message with details of server from which it had accepted the offer.

If network is configured with multiple DHCP servers, only one offer accepted

Other servers will withdraw any offers, returning IP address to available pool

42
Q

What is the 4th stage of the DHCP procedure

A

Acknowledgement:
when targeted DHCP server receives request message from client, config process enters final phase.

Packet is sent to client that includes any other config info that client requested

43
Q

What does port forwarding do

A

Allows remote computers to connect to a specific computer or service within private LAN

44
Q

Operation of port forwarding

A

Servers accessible to the public can be given a private IP address within private network

Public request reaches external router of private network using a given port

Data packets are forwarded internally to correct device

A Level AQA Computer Science (8 decks)

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