Classful Addressing
Classful Addressing 관련
The solution lies in providing some flexibility. Consider another approach called "classful addressing". In this approach, the number of bits dedicated for the network ID changes from one address to another, and you can tell the network ID by looking at the first, most-significant byte of the address.
- Any address starting with a number between
1and127belongs to "Class A", meaning that its network ID consists of 1 byte, leaving 3 bytes for the host ID. - Any address starting with a number between
128and191belongs to "Class B", which means that its network ID is 2 bytes long, and its host ID is also 2 bytes long. - Any address starting with a number between
192and223belongs to "Class C", so it has 3 bytes of a network ID, and 1 byte of host ID.
You can see the full representation of this approach in the table below:
| Class | First Byte Range | Network ID Size | Host ID Size |
|---|---|---|---|
| A | 1 - 127 | 1 byte | 3 bytes |
| B | 128 - 191 | 2 bytes | 2 bytes |
| C | 192 - 223 | 3 bytes | 1 byte |
| D | 224 - 239 | (multicast) | |
| E | 240 - 255 | (reserved) |
(Source:
BriefVid)For example, what class does this address belong to?
(1) 130.12.204.5
Since it starts with 130, which is between 128 and 191, it belongs to "Class B". This means that its network ID is 130.12, and its host ID is 204.5. Let's mark it as "address number 1".
Do this address and the following address (2) belong to the same network?
(2) 130.90.2.40
No, since they have different network identifiers, they are not within the same network.
What class does the following address belong to?
(3) 200.1.1.9
It belongs to class C, as the value of its first byte, 200, is between 192 and 223. This means that its network identifier is 200.1.1, and any address starting with this prefix will reside within the same network. This specific address describes host 9 within this network.
To complete the picture, addresses starting with a value between 224 and 239 belong to "Class D" – that is, multicast addresses – addresses that belong to multiple devices. Addresses starting with a value between 240 and 255 were reserved for future use. Addresses starting with 0 are special addresses.
IP Address Assignment
In the early internet, IPv4 addresses were assigned to organizations by the Internet Assigned Numbers Authority (IANA). As the internet grew, this responsibility was distributed to five Regional Internet Registries (RIRs) that handle address allocation for different geographic regions. Large organizations would receive blocks of addresses based on their needs, with address classes determining the size of these blocks.
What are the disadvantages here? 🤔
While classful addressing allows for more flexibility compared to the fixed-length approach, even this approach isn't flexible enough.
Consider this scenario: A small startup company with just two founders needs a network identifier. Which class would they need?
Getting a class A or class B would be excessive, so they might get a class C – allowing 256 addresses. This is more than currently needed, but allows some expansion. What happens if the startup grows to more than 256 employees (and devices)?
At this point, they would need to get a class B address, giving no less than 65,536 addresses, when all they need is a bit over 256 addresses. This means wasting more than 60,000 addresses.
This became a real problem in the early 1990s as the internet was growing faster. The need for more IP addresses became apparent, and there was an impending exhaustion of the IPv4 address space. Cases where 60,000 addresses were wasted could no longer be tolerated.