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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 8 Configuring Interface Characteristics
Using the Interface Command
Figure 8-2
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. 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 with
the enhanced multilayer software image 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 22, “Configuring IP Unicast Routing,”
Chapter 24, “Configuring IP Multicast Routing,”
and
Chapter 25, “Configuring MSDP.”
•
Fallback bridging forwards traffic that the switch with the enhanced multilayer software image does
not route or traffic belonging to a nonroutable protocol, such as DECnet. Fallback bridging connects
multiple VLANs into one bridge domain by bridging between two or more SVIs or routed ports.
When configuring fallback bridging, you assign SVIs or routed ports to bridge groups with each SVI
or routed port assigned to only one bridge group. All interfaces in the same group belong to the same
bridge domain. For more information, see
Chapter 26, “Configuring Fallback Bridging.”
Using the Interface Command
The Catalyst 3550 switch supports these interface types:
•
Physical ports—including switch ports and routed ports
•
VLANs—Switch Virtual Interface
•
Port-channels—EtherChannel of interfaces
You can also configure a range of interfaces (see the
“Configuring a Range of Interfaces” section on
page 8-9
).
Si
Host A
SVI 1
172.20.128.1
172.20.129.1
SVI 2
Catalyst 3550 switch
with enhanced multilayer
software image
VLAN 20
Host B
VLAN 30
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