Specifications

CHAPTER 5
Implementing High Availability
Designing for Redundancy
Figure 5-1 shows where you would typically use redundancy within a campus network. Access switches are either
chassis-based with dual Supervisor engines and dual power supplies or are stackable switches. They have redundant, fully
meshed links to redundant distribution switches, which, in turn, have redundant links to redundant core switches.
Distribution and core switch pairs are connected via a Layer 2 or Layer 3 link. This design minimizes single points of
failure and enables the network to recover from a link or switch failure.
Layer 2 Versus Layer 3 Access Design
You can use a Layer 2 or a Layer 3 access layer. When using L2, VLANs can either be distributed across multiple
switches or local to each switch. Figure 5-2 shows L2 access switches with VLAN 10 on both of them. This design is not
recommended. The FHRP Active switch and the STP Root must be statically configured as the same switch. STP blocks
one uplink per access switch. RSTP helps speed convergence.
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CCNP SWITCH 642-813 Quick Reference by Denise Donohue
FIGURE 5-1
Designing for
Redundancy
Access
Distribution
Core
Redundant Switches
Redundant Links
Redundant Switches
Redundant Links
Single Switches
with Dual SUPs,
or Stackable
Switches