Connecting Interfaces - Cisco WS-C3550-12G Software Configuration Manual

Chapter 8 Configuring Interface Characteristics
Understanding Interface Types
For more information about IP unicast and multicast routing and routing protocols, see Chapter 22,
"Configuring IP Unicast Routing" and Chapter 24, "Configuring IP Multicast Routing."

Connecting Interfaces

Devices within a single VLAN can communicate directly through any switch. Ports in different VLANs
cannot exchange data without going through a routing device or interface.
With a standard Layer 2 switch, ports in different VLANs have to exchange information through a router.
In the configuration shown in Figure 8-1, when Host A in VLAN 20 sends data to Host B in VLAN 30,
it must go from Host A to the switch, to the router, back to the switch, and then to Host B.
Figure 8-1 Connecting VLANs with Layer 2 Switches
Cisco router
Switch
Host A Host B
VLAN 20 VLAN 30
By using the Catalyst 3550 with the enhanced multilayer software image installed, when you configure
VLAN 20 and VLAN 30 each with an SVI to which an IP address is assigned, packets can be sent from
Host A to Host B directly through the Catalyst 3550 switch with no need for an external router
(Figure 8-2).
Catalyst 3550 Multilayer Switch Software Configuration Guide
8-5
78-11194-03