[Day 2] 3. Routers and Subnets

Routers: Connect different networks and prevent broadcast overload by limiting the number of devices per network.
Routers are very costly and come with limited ports.
IP Addressing: Consists of a 32-bit address (
```
w.x.y.z
```
) and a subnet mask that distinguishes between the network and host portions of the address.
Classes of IP Addresses (Note: Classful addressing is largely obsolete, replaced by CIDR):
- Class A: Large organizations (
```
1-126
```
  ,
```
255.0.0.0
```
  ).
- Class B: Medium-sized organizations (
```
128-191
```
  ,
```
255.255.0.0
```
  ).
- Class C: Small networks (
```
192-223
```
  ,
```
255.255.255.0
```
  ).
- Class D: Reserved for multicasting.
- Class E: Experimental use.

Subnetting

Subnet Masks: Divide IP addresses into networks and hosts, with a strict division line between the two (e.g.,
```
255.255.255.0
```
for Class C).
Subnet Calculation: Number of possible subnets and hosts can be calculated using formulas like
```
2ⁿ - 2
```
(e.g.,
```
2⁸ - 2 = 254
```
usable host addresses, subtracting network and broadcast addresses).
CIDR Notation: Subnets can be represented with a
```
/
```
followed by the number of bits for the network part (e.g.,
```
/24
```
for
```
255.255.255.0
```
). This number represents the count of 1s in the subnet mask when written in binary.