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 individual devices or hosts on a network.

127.x.x.x is the loopback range, used for diagnostics on the local machine, not routable outside the device.

x.x.x.0 is the network identifier (network address) for the subnet — it identifies the whole network, not a host.

x.x.x.255 is the broadcast address on that subnet — used to send data to all hosts simultaneously.

x.x.x.1 is commonly used as the default router/gateway address, but this can vary depending on network setup.

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

Each class has fixed network and host portions.

Question 5

classful vs classless addressing

Answer 5

classful : number of hostID’s are fixed, the use of the suffix “/24” enables IP addresses to be used with varying proportions of host and network IDs

classless: number of hostID are variable

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

what is subnetting and why is it used

Answer 7

• the process of dividing a large network into smaller, more manageable sub-networks, or subnets
• reducing traffic and increasing control.

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 IP: globally unique, routable over the internet.

Private IP: used within LANs, not routable on the internet.
- Not allocated centrally
- impossible to connect
to over Internet // fromoutside
network

following are considered private:
- 10.0.0.1 - 10.255.255

Question 10

advantages of private IPs

Answer 10

Conserve public IPs: Many devices can use private IPs internally without needing public ones.

Enhance security: Private IPs are not directly accessible from the internet, reducing exposure.

Allow network flexibility: Private IP ranges can be reused in different networks without conflict.

Simplify internal network management: Easier to organize and control devices inside a local network.

Support NAT functionality: Private IPs work with NAT to connect to the internet via a shared public IP.

Question 11

number of possible hosts

Answer 11

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

Question 12

why is network address translation (NAT) used

Answer 12

Conserves public IP addresses by allowing multiple devices to share one public IP.

Enhances security by hiding internal IP addresses from the external network.

Enables use of private IP addresses within local networks.

Allows communication between different IP address schemes (private and public).

Simplifies IP address management within an organization.

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

Conserves IP addresses: Allows multiple devices on a local network to share a single public IP address.

Improves security: Hides internal IP addresses from external networks, reducing attack surface.

Enables private networks: Allows use of private IP addresses internally without conflict on the internet.

Simplifies IP management: Internal IPs can remain unchanged even if the external IP changes.

Supports IP address reuse: Private IP addresses can be reused across different networks.

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 that 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
• facilitates efficient use of a limited pool of IP addresses

Question 18

how does a DHCP system work

Answer 18

• The host sends a request to discover a DHCP server
• DHCP servers offer configuration to host
• host accepts offer of configuration from server
• DHCP server confirms that configuration has been allocated to host.
• 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

Question 24

reasons why IPv6 has been introduced to replace IPv4

Answer 24

• There are not enough (unique) addresses in IPv4
• Eliminate need for NAT / network address translation
• more efficient routing is possible;
• Improved facilities for multicasting;
• Automatic configuration possible without DHCP;
• Allows bigger packet sizes;

Question 25

private IP addresses:

Answer 25

10.0.0.1 - 10.255.255.255 172.16.0.1 -172.31.255.255 192.168.0.1 - 192.168.255.255

Question 26

Explain how a computer located outside an LAN can access the web server, despite the fact that the web server is identified by a non routable IP address

Answer 26

Computers will use the public IP address of the router / 186.7.2.31 (to access the web server); (The router will perform) port forwarding; Router maintains a port mapping table

Question 27

Describe how NAT processes the outgoing request and returned data when using FTP

Answer 27

**When request sent:** (When the router receives the FTP request from the computer), router will replace the IP address of the computer The router replaces the (source) port number with a port number it generates; The router adds the mapping ) it has created to its NAT translation table **When reply received** When a reply is received from the FTP server, it is recognised by its destination port number (If the port number is present in the NAT translation table) the reply is forwarded to the computer that made the original request (If the port number is present in the NAT translation table) the router replaces its IP address

Question 28

Why are private IP addresses not routable over the internet?

Answer 28

they are reserved for use within private networks and are not globally unique

Question 29

disadvantage of DHCP

Answer 29

potential for IP spoofing If the DHCP server fails, devices may not be able to connect to the network. Security risks: Unauthorized devices can connect if network access isn’t controlled. IP address conflicts: Can occur if leases overlap or are mismanaged.

Question 30

Explain why it might be undesirable to allow the network settings of the web server to be configured by a DHCP server.

Answer 30

The IP address of the web server might be changed (by the DHCP server); If the IP address of the web server changes, port forwarding will no longer work;

Question 31

why is nat not needed with ipv6

Answer 31

There are enough (IPv6) addresses for every device (in the world) to have a unique/public/routable (IP) address

Question 32

how does port forwarding work

Answer 32

**Router receives external request**: A device from the internet tries to connect to your public IP on a specific port. **Router checks port forwarding rules**: It looks for a rule matching that port number. **Request is forwarded**: The router forwards the data to the correct internal (private) IP and port inside the local network. **Device responds**: The internal device sends a response back through the router to the external device. Used for hosting: Common for allowing access to local services like game servers, CCTV, or web servers from outside.