The CompTIA A+ exam objectives asks you to explain IP addresssing so lets try to break it down for you here.
An Internet Protocol (IP) address is the unique identification number for your system on the network. Every single computer, printer, switch, router, or other networking device will have an IP address when it is part of a TCP/IP based network.
IP address can’t end with a 0 or 255
Static
- A static IP doesn’t change until someone manually changes it.
- A computer is not issued an IP until someone configures the IP, Default Mask, and Default Gateway in the Internet Protocol Version 4 (TCP/IPv4) Properties.
Dynamic
- Uses DHCP to automatically get an IP address
- Every time a client device is turned on it gets assigned an IP address from the DCHP server. After a certain amount of time, the IP address assignment expires and gets put back into the pool of available IP addresses that the DHCP server can distribute.
APIPA
- APIPA stand for Automatic Private IP Addressing
- APIPA automatically assigns an IP address when the client can’t obtain an IP automatically.
- APIPA range: 169.254.0.1 to 169.254.255.254 (169.254.x.y) – The first (169.254.0.0) and last (169.254.255.255) 256 addresses are reserved.
- A computer on a network with an active DHCP server that has an APIPA address indicates a problem connecting to the DHCP server.
- If a client workstation is unable to communicate with the Internet, check if the client has an APIPA address.
- The process of automatically assigning an IP address is done by the operating system. Before it assigns the IP address it sends an ARP (Address Resolution Protocol) frame out to the network to confirm the address isn’t currently in use.
- A client with an APIPA address will be able to communicate on a local connection but will fail to communicate outside of the local network
Link local
An APIPA address is a link local address. A link local address allows you to communicate to devices on your subnet, but you aren’t able to communicate outside of your local subnet.
Link local addresses are available for IPv4 and IPv6 addresses.
A link local address is automatically assigned to every IPv6 enabled device. The range for link local addresses for IPv6 begins with fe80 and then all zeroes with only one subnet allocated. This means effectively the link local address is fe80 with the rest zeroes in the first 64 bits and the last 64 bits are assigned as the node address. The last 64 bits that are assigned to the device are not always a random value. It can be created based off of the MAC address of the device.
Private IP Address Ranges
Private IP Addresses aren’t listed specifically on the CompTIA A+ exam objectives, but they are useful to know in the real world. IP addresses used on the Internet are called public addresses. Private IP addresses are not routable on the Internet. Instead, they are meant to be used on private networks. With a service called Network Address Translation (NAT), these multiple private nonrouteable IP addresses can be translated into a single public IP addresses. Therefore, any request coming from the internal network will appear to come form the single public IP.
| Class | IP Address Range | Default Subnet Mask | Number of Hosts |
| A | 10.0.0.0 – 10.255.255.255 | 255.0.0.0 | 16.7 million |
| B | 172.16.0.0 – 172.31.255.255 | 255.240.0.0 | 1 million |
| C | 192.168.0.0 – 192.168.255.255 | 255.255.0.0 | 65,536 |
