4.9.4.3-9 IP Addresses

What is an IP address?

Unique identifying number assigned to every device on a network

What is the structure of an IP address?

• Network identifier

• Host identifier

What is the network identifier?

Identifies the specific network a device is a part of, distinguishing it from other networks

→ Every device in a network will have the same

What is the host identifier?

Identifies the specific device within a network, allowing it to be uniquely addressed by other devices

What are subnets?

Smaller divisions of a larger network

→ Each subnet has own network identifier

How can the network identifier be determined?

Using a subnet mask

How does subnet masking work?

• A bitwise AND operation is performed on the IP address and subnet mask

• Mask identifies which bits are the network (1) and which are the host (0)

What is a common subnet mask?

255.255.255.0

How can the number of subnets increase?

With more bits assigned to the network identifier

What is the effect of increasing the number of bits assigned to the host identifier?

Increases the number of hosts per subnet

What are the types of IP address in common use?

• IPv4

• IPv6

What is the structure of IPv4 addresses?

• Four parts separated by dots

• Each part assigned one byte (0-255)

Roughly how many unique IPv4 addresses are there?

Over 4 billion

Why was IPv6 introduced?

• IPv4 addresses in short supply

• Number of devices on the Internet requiring a routable IP address is increasing rapidly

What is the structure of IPv6 addresses?

• Eight groups of four hexadecimal digits separated by colons

• Each group represents 16 bits

What are the forms of IP address?

• Routable (public)

• Non-routable (private)

Why aren’t all IP addresses routable?

There would not be enough to go around

How are routable IP addresses used by homes and businesses?

• Each has a small number of public IP addresses

• Most homes just have one

• Businesses may have multiple

What is the difference between routable and non-routable IP addresses?

• Routable are globally unique

• Millions of devices can have the same non-routable

Who is responsible for assigning routable IP addresses?

Global authorities

→ Ensures the same address is never used twice

How can IP addresses be wasted?

• Limited number of private IP addresses within a private network

• If every device had its own private IP address, those who leave and never join again are taking up an address for the network

What does DHCP stand for?

Dynamic Host Configuration Protocol

What is the purpose of DHCP?

Assigning IP addresses to devices as they join a network

How does DHCP work?

• Uses a pool of available IP addresses to allocate to new devices for the duration of their session

• When a device leaves, their IP address is returned to the pool so that it can be reused

What does NAT stand for?

Network Address Translation

What does NAT do?

• Router makes a record of the packet being sent by a device on the private network

• Replaces the private IP address of the device with its own routable address

• Responses are sent to the router’s public IP

• Fowarded to the correct private IP using the record made during sending

What does NAT allow?

• Multiple devices to share the same IP address, reducing wastage

• Improved security, as private addresses are not directly exposed

When is port forwarding used?

When a client needs to communicate with a server that is connected to a private network

How does port forwarding work?

• Client sends packets to public IP address of the router of the server’s network

• Packets contain the port number of the application running on the server that the client wishes to access

• Router forwards the packet to the server using NAT