Cisco WS-C3550-12G Software Configuration Manual page 45

Chapter 1 Overview
Network Configuration Examples
Small to Medium-Sized Network Using Mixed Switches
Figure 1-2 shows a configuration for a network of up to 500 employees. This network uses Catalyst 3550
multilayer switches to aggregate up to ten wiring closets through high-speed uplinks. For network
reliability and load balancing, this network includes two routers and two Catalyst 3550 multilayer
switches, all with HSRP enabled. This ensures connectivity to the Internet, WAN, and mission-critical
network resources if one of the routers or Catalyst 3550 multilayer switches fails.
The wiring closets have a mix of switches such as the Catalyst 3550, Catalyst 3500 XL, Catalyst 2950,
Catalyst 2900 XL, Catalyst 2820, and Catalyst 1900 switches. These switches are connected to
workstations, Cisco IP Phones, and local servers. You can cluster these switches into multiple clusters,
as shown, or into a single cluster. You can manage a cluster through the IP address of its primary and
secondary command switches, regardless of the geographic location of the cluster members.
This network uses VLANs to segment the network logically into well-defined broadcast groups and for
security management. Data and multimedia traffic are configured on the same VLAN.
When an end station in one VLAN needs to communicate with an end station in another VLAN, a router
or multilayer switch routes the traffic to the appropriate destination VLAN. In this network, the
Catalyst 3550 multilayer switches provide inter-VLAN routing. VLAN access control lists (VLAN
maps) on the Catalyst 3550 switches provide intra-VLAN security and prevent unauthorized users from
accessing critical pieces of the network.
In addition to inter-VLAN routing, the Catalyst 3550 multilayer switches provide QoS mechanisms such
as DSCP priorities to prioritize the different types of network traffic and to deliver high-priority traffic
in a predictable manner. If congestion occurs, QoS drops low-priority traffic to allow delivery of
high-priority traffic.
With the Catalyst 3550 multilayer switches providing inter-VLAN routing and other network services,
the routers focus on firewall services, Network Address Translation (NAT) services, voice-over-IP
(VoIP) gateway services, and WAN and Internet access.
Catalyst 3550 Multilayer Switch Software Configuration Guide
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