Design Guide

7
LAN Baseline Architecture Overview—Branch Office Network
OL-11333-01
Multilayered Branch Architecture
Figure 4 Traditional Highly-Available LAN Design
The Layer 2 access switch is connected to both the distribution switches, and the distribution switches
are connected together by a trunked EtherChannel. Typically, the Layer 2 topology is designed in such
a way that the spanning tree blocks predetermined links so that the traffic takes a deterministic path
under both normal and failure circumstances. The convergence problem is addressed by Rapid Spanning
Tree, which converges in the sub-second range under failure conditions. Misconfiguration always causes
problems when troubleshooting, but by following the appropriate design guide, this should not be a
problem for a trained engineer.
Figure 5 provides a different approach for using Layer 2 at the access layer.
Layer 3
Core
Or
Edge
Layer 2
Access
Distribution
Loop
Access Point
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