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  • Table of Contents
  • Layer 2 Technologies
    • Ethernet Switching
      • L2 Switch Operations
      • Spanning Tree
        • 802.1d – STP
        • 802.1w – RSTP
        • 802.1s – MSTP
      • VTP 101
      • Private VLANs
      • VLANs
      • EtherChannel 101
    • Layer 2 WAN Protocols
      • HDLC
        • HDLC 101
      • PPP
        • PPP 101
        • PPP Authentication - PAP
        • PPP Authentication – CHAP
        • PPP Authentication – EAP
        • PPP Multilink
        • PPPoFR – PPP over Frame Relay
        • PPPoE – PPP over Ethernet
      • Frame Relay
        • Frame Relay 101
        • Frame Relay 102
        • Frame Relay Encapsulations – IETF vs Cisco
        • Multilink Frame Relay
        • Frame Relay Switching
        • Routing over Frame Relay
      • Bridging
        • Bridging on a router
        • MTU 101
    • Wireless
      • Wireless Principles
      • Wireless Implementations
      • Wireless Roaming
      • Wireless Authentication
        • WPA2 PSK
        • WPA2 802.1X
  • IPv4
    • IPv4 Addressing
      • Backup Interfaces
      • FHRP 101
      • DHCP 101
      • DNS 101
      • ARP 101
      • IPv4 101
      • Tunnel Interfaces
        • GRE Tunnels
      • BFD – Bidirectional Forwarding Detection
    • IPv4 Routing
      • How the routing table is built
        • How CEF works
        • Routing Order of Operations
        • NSF – Non Stop Forwarding
      • RIP
        • RIP 101
      • EIGRP
        • EIGRP 101
        • EIGRP Metric
        • More EIGRP Features
      • OSPF
        • OSPF 101
        • OSPF Areas
        • OSPF LSAs
        • OSPF Mechanics
      • IS-IS
        • IS-IS 101
        • IS-IS Mechanics – CLNP
      • BGP
        • BGP 101
        • BGP Attributes
        • More BGP
      • Route Redistribution
      • Policy based Routing
      • PfR 101 – Perfromance Routing
      • ODR
  • IPv6
    • IPv6-101
    • IPv6 Routing
    • Interconnecting IPv6 and IPv4
  • MPLS
    • MPLS 101
    • MPLS L3 VPN
  • Multicast
    • Multicast 101
    • PIM 101
    • IGMP 101
    • Inter Domain Multicast
    • IPv6 Multicast
    • Multicast features on switches
  • Security
    • NAT 101
    • NAT for Overlapping Networks
    • ACLs 101
    • ACLs 102
    • Cisco IOS Firewall
    • Zone Based Firewall
    • AAA 101
    • Controlling CLI Access
    • Control Plane
    • Switch Security
      • Switchport Traffic Control
      • Switchport Port Security
      • DHCP Snooping and DAI
      • 802.1x
      • Switch ACLs
    • IPSec VPN 101
      • IKE / ISAKMP 101
      • IPSEC Crypto Maps 101
      • IPSEC VTI 101
      • DMVPN 101
    • EAP 101
  • Network Services
    • NTP 101
    • HTTP 101
    • File Transfer 101 – TFTP & FTP
    • WCCP 101
  • QoS
    • QoS 101
    • Classification and Marking
    • Congestion Management
      • Legacy Congestion Management
      • SPD – Selective Packet Discard
      • CBWFQ
      • IP RTP Priority
    • Congestion Avoidance – WRED
    • Policing and Shaping
      • CAR 101
    • Compression and LFI
      • Header and Payload Compression
      • LFI for MultiLink PPP
    • Frame Relay QoS
      • Per VC Frame Relay QoS
    • RSVP 101
    • Switching QoS
  • Network Optimization
    • NetFlow 101 – TNF – Traditional NetFlow
    • NetFlow 102 – FNF – Flexible NetFlow
    • IP SLA 101
    • IP Accounting 101
    • Logging 101
    • SNMP and RMON 101
    • Cisco CLI Tips and Tricks
    • AutoInstall
    • Enhanced Object Tracking
    • Troubleshooting 101
    • SPAN, RSPAN, ERSPAN
  • Network Architecture
    • Hierarchical Network Architecture
    • SD Access
    • SD WAN
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  • Hierarchical LAN Design
  • Access Layer
  • Distribution Layer
  • Core Layer
  • Hierarchical Design Options
  • The 3 Tier Design
  • Collapsed Core - The 2 Tier Design
  • Access Layer Design Options
  • Simplified Distribution Layer

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  1. Network Architecture

Hierarchical Network Architecture

PreviousSPAN, RSPAN, ERSPANNextSD Access

Last updated 2 years ago

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Hierarchical LAN Design

When building a network it is a great advantage to follow a structured, hierarchical approach. The Hierarchical LAN Design breaks a complex networks into several layers that can provide improved resiliency, fault isolation and simplified maintenance.

The Hierarchical LAN Design comprises of 3 layers: Access, Distribution and Core.

At each aggregation layer the complexity is reduced from N*(N-1) connections needed to mesh connect N devices down to 2*N (when using individual links to a redundant aggregation devices) or even N (when using link aggregation to the aggregation devices).

Access Layer

  • Provides access to the network for endpoints and users. This means it also should support various technologies to accomodate different type of devices and network needs - for example, PoE (Power over Ethernet.

  • It is the network boundary and therefore it acts as security, QoS and policy trust boundary. The access layer must protect the network from human errors and malicious attacks

  • Traditionally access layer devices operate as L2 only devices but more modern takes on the design of the Access Layer will support devices operating at L3.

Distribution Layer

  • aggregates the access layer and provides connectivity from one access layer device to another, or to the WAN or other services.

  • Traditionally access layer has devices operating at both L2 (towards the Access Layer) and L3 (towards the Core Layer).

Core Layer

  • is used to aggregate multiple distributions. Without a core layer the distribution layer devices would need to be fully mashed.

  • It must be designed to provide packet swithing as fast as possible.

  • Devices of the Core Layer operate almost always as L3 devices.

Hierarchical Design Options

The 3 Tier Design

The 3 Tier design contains all three layers and makes use of the Core Layer to interconnect multiple distributions.

Collapsed Core - The 2 Tier Design

This design usually works for smaller deployments where the effort of adding and maintaining a Core Layer to connect the distributions would not reduce the complexity enough. In a collapsed core design, the Core Layer functionality is provided by the distribution layer.

Using the complexity formula to figure out when a collapsed core would be more beneficial than The 3 Tier Design, N*(N-1) is higher than 2*N when N is higher than 3.

Access Layer Design Options

    • Looped Design

    • Loop Free Design

      • Is less common because it requires that each access switch supports a single VLAN which limits the flexibility of the network

  • Layer 3 Access

    • This option moves the L2 boundry to the access switch, effectively avoiding the L2 loops and making use of all possible paths. However not all applications can work in a L3 only network and still require L2 connectivity between hosts.

Simplified Distribution Layer

This design is called simpliefied because it makes use of technologies such as VSS (Virtual Switch System) or Stackwise.

Using VSS

  • VSS is usually used at the Distribution Layer and makes the (usually redundant) distribution devices work as a single logical device.

  • The Distribution Layer devices transfer control layer information over a Virtual Switch Link.

  • The design makes use of MEC (Multichassis EtherChannel) connections which bundles multiple physical links into a single logical link.

  • Since the VSS switch works as a single logical device there is no need for FHRP protocols for gateway redundancy.

Using Stackwise

  • Stackwise can be used at the Access Layer and can connect multiple devices into a single logical link

  • The devices that are part of a stack exchange control plane information using the Stackwise Interconnect ring.

  • The design makes use fo standard EtherChannel since the bundled links are between the same two devices.

Resources

Traditional Layer 2 Access should be used with a Distribution Layer that makes use of a protocol to provide gateway redundancy for a VLAN.

In the looped design must be used to break the loops. This will block traffic on some of the links thus making resource utilization sub-optimal

FHRP
STP
Campus LAN and Wireless LAN Solution Design Guide
Hierarchical LAN Design
Collapsed Core Design
Traditional vs VSS vs Stackwise