Specifications

ii
Cisco 1751 Router Software Configuration Guide
OL-1070-01
• Security
• Broadcast Control
• Performance
• Network Management
• Communication Between VLANs
LAN Segmentation
VLANs allow logical network topologies to overlay the physical switched infrastructure such that any
arbitrary collection of LAN ports can be combined into an autonomous user group or community of
interest. The technology logically segments the network into separate Layer 2 broadcast domains
whereby packets are switched between ports designated to be within the same VLAN. By containing
traffic originating on a particular LAN only to other LANs in the same VLAN, switched virtual
networks avoid wasting bandwidth, a drawback inherent to traditional bridged and switched networks
in which packets are often forwarded to LANs with no need for them. Implementation of VLANs also
improves scalability, particularly in LAN environments that support broadcast- or multicast-intensive
protocols and applications that flood packets throughout the network.
illustrates the difference between traditional physical LAN segmentation and logical VLAN
segmentation.
Table 1 LAN Segmentation and VLAN Segmentation
Catalyst
VLAN switch
VLAN 1
VLAN segmentationTraditional LAN segmentation
VLAN 2 VLAN 3
LAN 1
Shared hub
Shared hub
Shared hub
Floor 3
Floor 2
Floor 1
LAN 2
LAN 3
S6619
Catalyst
VLAN switch
Catalyst
VLAN switch
Router
Router