IP addresses

Question 1

what does IPV4 use

Answer 1

octets(group of 8 bits) and its a 32 bit number

Question 2

summarise unusable/reserved addresses

Answer 2

• some IP addresses cannot be used for an individual network or host
  eg:
• 127.x.x.x, non routable addresses, used for diagnostics within local network
• x.x.x.0 is the network identifier
• x.x.x.255 is reserved as the broadcast address on that subnet, where data is sent simultaneously to all subnetwork hosts
• x.x.x.1 is the default router address

Question 3

parts of an IP address

Answer 3

networkID - left hand bits used to define the network where nodes are communicating
HostID - right hand bits, used to identify the nodes on the network

Question 4

summarise classful addressing

Answer 4

when the network ID is given at the end of the IP address, eg 210.54.101.0/24 has a network ID of 24

Question 5

summarise classful IP addressing

Answer 5

IP addresses being categorised into classes to identify network ID and host IDs of various ranges

Question 6

summarise subnet masking

Answer 6

• a subnet mask is used with an IP add to identify the 2 unique parts of the address
• subnet mask has all network ID bits set to 1, and all host IDs set to 0
• bitwise AND is used with the IP and the network is identified

Question 7

summarise subnetting

Answer 7

• an organisation can create subnetwork segments within their IP network in order to ease management

Question 8

advantages of subnetting

Answer 8

• improves efficiency by routing data through one segment only
• reduces the size of the broadcast domain, which can improve security
• can reduce data collisions

Question 9

public vs private IPs

Answer 9

• public IPs must be globally unique, and be able to be addressed directly by any computer
• priv IPs do not need to be globally unique and dont require internet registry

following are considered private:
- 10.0.0.1 - 10.255.255

Question 10

advantages of private IPs

Answer 10

reduces the need for every computer to have its own unique public address

Question 11

number of possible hosts

Answer 11

2^32 - 2
because they cane end in 255 or 0

Question 12

summarise network address translation (NAT)

Answer 12

• used to convert IP addresses as they pass between a public address space (using a public IP ) and an LAN with a priv address space
• they are required to translate private IPs as they are not routable , therefore cant be used for routing packets on the Internet

Question 13

advantages of NAT

Answer 13

allows a single public IP address to be shared by any number of hosts with a private IP

Question 14

NAT process

Answer 14

• the translation device records the source and destination socket address for each request
• it then communicates on the hosts with the destination IP address
• when a response returns, it is passed back to the host that made the original request

Question 15

what is port forwarding

Answer 15

• a networking technique used to redirect communication requests from one address and port number to another
• while the packets are traversing a network
• typically through a router or firewall
• Allows external devices to access services on a private network.

Question 16

what is the purpose of a DHCP system

Answer 16

to automate the configuration of hosts connecting to a TCIP/IP network

Question 17

advantages of a dhcp system

Answer 17

• reduces the need for expert knowledge when configuring a host
• reduced the time required to configure host

Question 18

how does a DHCP system work

Answer 18

• The host broadcasts a DHCP Discover message to find available DHCP servers.
• DHCP server responds with a DHCP Offer containing available IP addresses and network settings.
• host sends a DHCP Request message to the chosen server, indicating it accepts the offered IP address.
• The server responds with a DHCP Acknowledgment (ACK), confirming the IP address and providing additional configuration details.
• The host configures its network interface using the IP address and configuration details provided by the server.

Question 19

explain how an external router would be configured so that a web server can be accessed by computers outside of the network

Answer 19

• traffic arriving on the HTTP port must be forwarded by
• the external router to the IP address of the web server

Question 20

Explain how:
* Computer A will use a subnet mask to determine whether or not it can send the
packet directly to Computer B across the LAN or if the packet must be sent via the
Internet

Answer 20

• AND operation of subnet mask with Computer A’s IP address
• AND operation of subnet mask with Computer B’s IP address
• result (of each AND operation) is the network/subnet ID
• network/subnet IDs compared
• as they are different, then packet must be sent via gateway, Computer B is not on the same subnet
• if they were the same, then Computer B
  is on the same subnet.

Question 21

explain how a packet will be routed across the Internet

Answer 21

• hierarchical organisation of routers
• path to take selected by each router
• (possible) repackaging of packet to use different protocol
• use of router tables to determine next hop
• router decrementing “time to live” of packet
• route determined using IP addresses

Question 22

how can the checksum be used to determine if the received packet has been changed
during the transmission.

Answer 22

checksum produced when packet transmitted
* (hash) value calculated from packet contents
* this value appended to packet
* computer B recalculates checksum
* received and calculate checksum compared
* if these match packet contents/data are accurate . if these differ the data has been
changed // if these differ there is an error in the data.

Question 23

explain how two or more computers connected to the Internet can have the same IP address and still communicate with each other

Answer 23

• the computers have private IP addresses
• so NAT will be performed
• so that the computers can communicate on the internet