Cisco Catalyst 6880-X Specifications download pdf (Page 44)

Distribution Layer April 2014

Figure 16 - Traditional looped design with VLANs spanning access switches

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VLAN 30

Interface

Blocked

Interface

Blocked

VLAN 30

Routed Access Distribution Layer Design

In another approach to access and distribution layer design, you can use Layer 3 all the way to the access layer.

The benefits of this design are that you eliminate spanning tree loops and reduce protocols because the IP

gateway is now the access switch. Because there are no spanning-tree blocking links, you can use both uplinks

to the access layer and increase effective bandwidth available to the users.

The challenge with the routed access layer design is that the Layer 2 domains are confined to a single access

closet, which limits flexibility for applications that require Layer 2 connectivity that extends across multiple access

closets.

Simplied Distribution Layer Design

The distribution layer design chosen for the campus design uses multiple physical switches that act as a single

logical switch or a single, highly-redundant physical switch. One advantage of this design is that spanning tree

dependence is minimized, and all uplinks from the access layer to the distribution are active and passing traffic.

Even in the distributed VLAN design, spanning tree blocked links due to looped topologies are eliminated. You

reduce dependence on spanning tree by using EtherChannel to the access layer with dual-homed uplinks. This is

a key characteristic of this design and you can load balance up to eight links if needed for additional bandwidth.

Figure 17 - Simplified design with a VLAN per access switch

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VLAN 30

VLAN 40

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Cisco Catalyst 6880-X Specifications Page 44