Cisco Catalyst 2000 Configuration Handbook page 39

18 Cisco LAN Switching Configuration Handbook
Note the use of
dual redundant
uplinks into the
next-higher layer
for high
availability
Figure 2-1 Layers of a Hierarchical Network Design
To provide high availability, each switch in a network layer needs to have dual or
redundant uplinks to two switches in the next higher layer. If a link failure or the fail-
ure of an entire switch occurs, the extra uplink can be quickly used. The uplink
failover is handled by the Spanning Tree Protocol (STP) at Layer 2 or by routing
protocols at Layer 3.
Place switching functionality at each layer of the hierarchy.
3.
■
■
■
Identify resources in your network that serve common functions. These become the
4.
modules or building blocks of your network design. Figure 2-2 shows some exam-
ples of these blocks and how they fit within the network hierarchy.
Switch Block 1
Si
Access: Switches at this layer generally have a high port density, lower cost, fea-
tures that address user access or security, and several high-speed uplink ports.
Usually, Layer 2 switching is sufficient, although Layer 3 switching can provide
higher availability for applications such as IP telephony.
Distribution: Distribution switches have a port density consisting of high-speed
ports and offer higher switching performance, ideally at Layer 3.
Core: The core layer should be built from the highest performance switches in
the network, aggregating traffic from the distribution switches. Layer 2 switches
can be used effectively, although switching at Layer 3 adds higher availability
and enhanced QoS. Usually a dual-switch core layer is sufficient to support an
entire enterprise.
Si
Si
Si
Si
Si
Switch Block 2
Si
Access
Distribution
Core