Information Technology Reference
In-Depth Information
Use the distribution switches to connect Layer 2 VLANs that span multiple access
layer switches.
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Summarize routes from the distribution to the core of the network to reduce routing
overhead.
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Use Virtual Switching System (VSS) as an option described in the following para-
graph to eliminate the use of STP and the need for HSRP.
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VSS solves the STP unused blocked links problem by converting the distribution switch-
ing pair into a logical single switch. With VSS, the physical topology changes as each ac-
cess switch has a single upstream distribution switch versus having two upstream
distribution switches. VSS is configured only on Cisco 6500 switches using the VSS Su-
pervisor 720-10G. As shown in Figure 3-8, the two switches are connected via 10GE links
called virtual switch links (VSL), which makes them seem as a single switch. The key bene-
fits of VSS include
Layer 3 switching can be used toward the access layer.
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Simplified management of a single configuration of the VSS distribution switch.
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Better return on investment (ROI) via increased bandwidth between the access layer
and the distribution layer.
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Traditional with STP
Between Access and
Distribution Layers
VSS 1440 Allows
Both Upstream Links
to Be Used
VSS Logical View
STP Blocked Links
Figure 3-8
Virtual Switching System
Core Layer Best Practices
Depending on the network's size, a core layer might or might not be needed. For larger
networks, building distribution switches are aggregated to the core. This is called a col-
lapsed core. This provides high-speed connectivity to the server farm / data center and to
the enterprise edge (to the WAN and the Internet).
Figure 3-9 shows the criticality of the core switches. The core must provide high-speed
must support gigabit speeds and data and voice integration.
