Cisco - Enterprise Campus Network Design

Collision Domain

  • A shared network segment upon which multiple hosts compete for usage
  • Collisions occur when two or more hosts attempt to transmit at the same time
  • Network segmentation is used to reduce the sie of a collision Domain
  • Switches allow for micro segmentation where each port on the switch is its own collection when running at full duplex

Broadcast Domain

  • Broadcast traffic is seen by all hosts on the segment
  • Excessive broadcast traffic causes performance problems and can monopolise bandwidth
  • Size of broadcast domains can be reduced by segmenting networks into VLANs

VLAN

  • Defines the boundary of a broadcast domain
  • Passing traffic between VLANs requires a Layer 3 device

Predictable Network Model

  • Low maintenance
  • High Availability
  • Designed around traffic flows, not type of traffic
  • Arranged so users are a consistent distance from needed resources

Hierarchical Network Design

  • Efficient, Intelligent, Scaleable, Easily Managed
  • Distinct Layers of devices
    • Core
    • Distribution
    • Access
  • Traffic Flow type
    • Local
    • Remote
    • Enterprise

Access Layer

  • End user connectivity at Layer 2 (VLANs)
  • Building Access Switches
  • High Port Density with Low Cost Per Port
  • Scaleable Uplinks with High Availability
  • Converged Network Services (Data, Voice, Video)
  • Security Features and QoS

Distribution Layer

  • Interconnects the Access and Core Layers
  • Building Distribution Switches
  • Aggregation of Multiple Access Layer Switches
  • High Layer 3 Routing Throughput, Layer 3 Boundary For Access Layer VLANs
  • Security And Policy Based Functions
  • QoS
  • Scaleable and redundant high speed links to Core and Access layers

Core Layer

  • Connectivity Between Switches in the Distribution Layer
  • Backbone
  • Switches traffic as efficiently as possible
  • Very High Layer 3 Routing Throughput
  • No unnecessary Packet Manipulation
  • Redudancy and Resilience
  • Advanced QoS
  • Smaller networks may combine core and distribution layers, known as a collapsed core. Not an independent building block

Best Practices

  • Design each layer with a Pair of switches
  • Connect each switch to next layer with redudant links
  • Connect each pair of distribution switches with at least one link
  • Do not connect access layers unless a stack or chassis switch
  • Do not extend VLANs beyond distribution switches

Modular Network Design

  • Permits the network to grow in a logical predictable manner
  • A switch block is a group of access layer switches with one or more distribution layer switches
  • Takes redudancy and scaleability into account
  • Core/Backbone layer used to connect all switch blocks
  • Other elements (such as a Datacenter block) can be added as needed

Switch Block Sizing

  • Traffic Types andd Behaviour
  • Size and number of common workgroups

Oversized switch block problems

  • Bottlenecks at distribution layer (CPU, Memory, Throughput, etc)
  • Broadast/Multicast traffic slows the switches in the switch block

Switch Block Redundancy

  • Multiple Power Supplies on different power sources
  • Multiple distribuion switches
  • Use a FHRP on the destribution switches (HSRP, VRRP, GLBP)
  • Avoid Layer 2 loops where possible
  • Do not use same VLAN across multiple access switches

Network Core

  • Required to connect two or more switch blocks
  • As efficient and reliable as possible
  • Links between core and distribution shoul be layer 3
  • Consider average aggregate link utilisation when scaling links
  • Deploy two multilayer switches (MLS) as a dual-core for Redundancy
  • Add more core switches to form a multi-node core when needed, fully mesh if possibble
  • Number of core switch peerings is limited only by number of distribution layer switches

Choosing Cisco products to use at each layer

  • Access Layer - High Port Densityy, Low Cost
    • 2960-X, 3650, 3850 with 48 ports each
    • 4500E For a single chassis switch
  • Distribution/Core Layer - High Layer 3 Switching Throughput, High Density, High Bandwidth Ports
    • 4500-X, 45000E, 6807-XL
    • 3750-X For smaller switch blocks/networks

Traffic Flow Paths

  • Local (Access Layer Only)
  • Remote (Access To Distribution)
  • Enterprise (Access To Distribution To Core)