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Architecture CCNP Enterprise Core (350-401) Cisco

Enterprise Network Architecture Options – Layer 2 Access Layer (Spanning Tree Protocol Based)

A traditional local area network design uses a Layer 2 access layer with a Layer 3 distribution layer.

The distribution Layer 3 provides the network gateway for the Layer 2 access layer hosts.

Where possible, it is recommended to restrict a VLAN to a single access layer switch to eliminate topology loops which are a common point of failure in local area networks; even with spanning tree protocol enabled.

This recommendation comes at the cost of flexibility as all hosts within a VLAN are restricted to a single access layer switch.

Where this recommendation is not used, and a Layer 2 VLAN is extended across multiple switches to provide access to an application or service, it is common to see STP block links and as a result cause slower network convergence.

To provide a degree of redundancy in the network design, a first hop redundancy protocol (FHRP) can be configured between two switches on the distribution layer to provide a reliable MAC and IP address for hosts to use as as gateway.

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