Campus and Enterprise: Network Design Layers

What do we need to plan for when designing a network:

Physical equipment:

• Switches
• Routers
• Servers for central services (DHCP, DNS…)
• Cabling
• Wireless

Equipment placement and connectivity

IP Addressing and subnet design

Network security and segmentation

Equipment Placement

Hierarchical Internetworking Model:

Multi-tier architecture divides enterprise networks into three or for layers:

Border (not in all architectures)

• Connect to Internet (Routing/Layer 3)

Core

• Dumb and Fast (Switching/Layer 2)

Distribution:

• Smart! (Routing/Layer 3)

Access (or Edge) layer

• Wireless AP’s and Switches
• Access VLANs (Layer 2)

Access (Edge) Layer

End-stations and servers connect to the enterprise at the access layer.

Access layer devices are usually commodity switching platforms (aka switches and wireless access points)

This layer is also called the desktop layer because it focuses on connecting client nodes, such as workstations to the network.

Layer 2 Technology like VLANs

Distribution Layer

The distribution layer is the smart layer in the three-layer model.

Routing, filtering (internal firewalling), and QoS policies are managed at the distribution layer.

Distribution layer devices also often manage individual branch-office WAN connections.

Typically handled by Multi-Layer switches (aka – switches that route) So, “Layer 3 switches” meaning that they can also deal with IP addresses

Core Layer

The core network provides high-speed, highly-redundant forwarding services to move packets between distribution-layer devices in different regions of the network.

Core switches and routers are usually the most powerful, in terms of raw forwarding power, in the enterprise;

Core network devices manage the highest-speed connections, such as 10, 40, or 100 gbps.

However, they are typically pretty dumb - just switching (layer 2)

Often don’t need much configuration - just links the distribution layers to each other - and to the Border

AKA – the network backbone

Border Layer

Simply – the network devices that connect an enterprise network to the Internet

Routers, border firewall, border load balancers, border IPS and other security devices

Layer 3 and up

Campus Example

Device: Layer

Device	Examples	What connects to it	What does it connect to	Layer
End-Station	Laptop,Desktop,Printer, Server…	Nothing	Switches, Wireless APs	Access
Edge Switch	48-port Ethernet for classroom	End-Stations	Distribution Switch	Access
Distribution Switch	Layer 2/3 (MLS) switch. Multiport with Fiber	All Edge Switches in a building - region	Core Switch	Distribution
Core Switch	High Speed-chassis-based switch. Lots of Fiber	Multiple Distribution switches and other Core switches	Other Core Switches (for redundancy), Border	Core
Border Devices	Border Router,Firewall, IPS	Core Switches	Internet	Border