Subnet and IPv4 Classes
Last updated on August 13, 2024 am
Subnet & IPv4 Classes
Subnet & Subnet Mask
For a random IP address a.b.c.d/x, x denotes the number of 1s in the subnet mask, starting from the most significant bits.
Divided by the subnet mask, the whole IP address can be seen as two parts: the network prefix and the host identifier.
For example, 192.168.19.123/20 is:
| Address Type | Decimal | Binary |
|---|---|---|
| IP Address | 192.168.19.123 |
11000000.10101000.00010011.01111011 |
| Subnet Mask | 255.255.240.0 |
11111111.11111111.11110000.00000000 |
| Host Identifier | 0.0.3.123 |
00000000.00000000.00000011.01111011 |
| Network Prefix | 192.168.16.0 |
11000000.10101000.00010000.00000000 |
| First Available Address | 192.168.16.1 |
11000000.10101000.00010000.00000001 |
| Last Available Address | 192.168.31.254 |
11000000.10101000.00011111.11111110 |
| Broadcast Address | 192.168.31.255 |
11000000.10101000.00011111.11111111 |
The subnet is always referred as its network prefix. It is used for routing outside the subnet.
Inside the subnet, connection and communication only care about the host identifier.
This two-layer separation makes routing more efficient and convenient.
IPv4 Classes
It’s wroth to note that IPv4 classes are already deprecated.
| Class | Decimal | Binary |
|---|---|---|
| A Start | 1.0.0.0 |
00000001.00000000.00000000.00000000 |
| A Private Start | 10.0.0.0 |
00001010.00000000.00000000.00000000 |
| A Private End | 10.255.255.255 |
00001010.11111111.11111111.11111111 |
| A End | 127.0.0.0 |
01111111.00000000.00000000.00000000 |
| A Mask | 255.0.0.0 |
11111111.00000000.00000000.00000000 |
| B Start | 128.0.0.0 |
10000000.00000000.00000000.00000000 |
| B Private Start | 172.16.0.0 |
10101100.00010000.00000000.00000000 |
| B Private End | 172.31.255.255 |
10101100.00011111.11111111.11111111 |
| B End | 191.255.0.0 |
10111111.11111111.00000000.00000000 |
| B Mask | 255.255.0.0 |
11111111.11111111.00000000.00000000 |
| C Start | 192.0.0.0 |
11000000.00000000.00000000.00000000 |
| C Private Start | 192.168.0.0 |
11000000.10101000.00000000.00000000 |
| C Private End | 192.168.255.255 |
11000000.10101000.11111111.11111111 |
| C End | 223.255.255.0 |
11011111.11111111.11111111.00000000 |
| C Mask | 255.255.255.0 |
11111111.11111111.11111111.00000000 |
| D Start | 224.0.0.0 |
11100000.00000000.00000000.00000000 |
| D End | 239.255.255.255 |
11101111.11111111.11111111.11111111 |
| E Start | 240.0.0.0 |
11110000.00000000.00000000.00000000 |
| E End | 255.255.255.255 |
11111111.11111111.11111111.11111111 |
Quote
拥塞如果不加控制的话，它坏的程度会非常坏，就是这个概念。你不在适合的节点，和传染病一样切入一下，它传染的速度会非常快，扩张的速度会非常快。这是一个非线性的思维。那么人啊，基本上都是线性的思维。有些事情是非线性的。所以说人啊，不管是人本身，还是机器本身，在处理这些非线性的时候，通常会造成一些误判。