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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 10 Configuring Interface Characteristics
Understanding Interface Types
Figure 10-1 Connecting VLANs with Layer 2 Switches
By using the Catalyst 3550 with routing enabled, 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 10-2).
Figure 10-2 Connecting VLANs with the Catalyst 3550 Multilayer Switch
The Catalyst 3550 switch with the enhanced multilayer software image supports two methods of
forwarding traffic between interfaces: routing and fallback bridging; the standard software image
supports only basic routing (static routing and RIP). Whenever possible, to maintain high performance,
forwarding is done by switch hardware. However, only IP version 4 packets with Ethernet II
encapsulation can be routed in hardware. All other types of traffic can be fallback bridged by hardware.
• The routing function can be enabled on all SVIs and routed ports. The Catalyst 3550 switches route
only IP traffic. When IP routing protocol parameters and address configuration are added to an SVI
or routed port, any IP traffic received from these ports is routed. For more information, see
Chapter 31, “Configuring IP Unicast Routing,” Chapter 34, “Configuring IP Multicast Routing,”
and Chapter 35, “Configuring MSDP.”
Host A
Switch
Cisco router
VLAN 20
Host B
VLAN 30
46647
Si
Host A
SVI 1172.20.128.1 172.20.129.1SVI 2
Catalyst 3550 switch
with routing enabled
VLAN 20
Host B
VLAN 30
86392
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