Cisco WS-C3550-12G Software Configuration Manual page 47

Chapter 1 Overview
Network Configuration Examples
Large Network Using Only Catalyst 3550 Switches
Switches in the wiring closet have traditionally been Layer 2-only devices, but as network traffic
profiles evolve, switches in the wiring closet are increasingly employing multilayer services such as
multicast management and traffic classification. Figure 1-3 shows a configuration for a network
exclusively using Catalyst 3550 multilayer switches in the wiring closets and a Catalyst 6000 switch in
the backbone to aggregate up to ten wiring closets.
In the wiring closet, each Catalyst 3550 switch has IGMP snooping enabled to efficiently forward
multimedia and multicast traffic. QoS ACLs that either drop or mark nonconforming traffic based on
bandwidth limits are also configured on each switch. VLAN maps provide intra-VLAN security and
prevent unauthorized users from accessing critical pieces of the network. QoS features can limit
bandwidth on a per-port or per-user basis. The switch ports are configured as either trusted or untrusted.
You can configure a trusted port to trust the CoS value, the DSCP value, or the IP precedence. If you
configure the port as untrusted, you can use an ACL to mark the frame in accordance with the network
policy.
Within each wiring closet is a Catalyst 3550 multilayer switch for inter-VLAN routing. These switches
provide proxy ARP services to determine IP and MAC address mapping, thereby removing this task
from the routers and lessening this type of traffic on the WAN links. These switches also have redundant
uplink connections to the backbone switches, with each uplink port configured as a trusted routed uplink
to provide faster convergence in case of an uplink failure.
The routers and Catalyst 6000 multilayer backbone switches have HSRP enabled for load balancing and
redundant connectivity to guarantee mission-critical traffic.
Catalyst 3550 Multilayer Switch Software Configuration Guide
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