Cisco Three-Layer Hierarchical Design..!!

 Cisco Has 3 layers.

1. Core Layer.
2. Distribution Layer.
3. Access Layer.

Core Layer

In the core Layer, We use devices called high-end routers and Those routers are going to be the gateway to the internet or outside our network. Basically, we use the redundancy internet connection where we do the path manipulation, Layer-3 security .

 we must have redundancy in the core for routing .

Distribution Layer.

In the distribution Layer , we use normally routers or layer 3 switches for QOS implementation, Layer 3 routing , vlan gateway ,etc etc . 

Access Layer.

In access layer we have lots of devices like our access switches and Access points from where our end hosts are connected, this is just an entry for all of our network for hosts .  Normally the switches we use are 3550,2960, SMB switches etc etc .

From the configuration point of view, we may have VLAN access, Layer-2 QOS marking, or maybe some layer-2 security features like Dhcp Snooping, Storm control etc.