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Catalyst 3750 Metro Switch Software Configuration Guide
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Chapter 9 Configuring Interface Characteristics
Using Interface Configuration Mode
Figure 9-2 Connecting VLANs with a Layer 3 Switch
The switch supports two methods of forwarding traffic between interfaces: routing and fallback bridging.
Whenever possible, to maintain high performance, forwarding is done by the switch hardware. However,
only IP version 4 packets with Ethernet II encapsulation can be routed in hardware. Non-IP traffic and
traffic with other encapsulation methods can be fallback-bridged by hardware.
• The routing function can be enabled on all SVIs and routed ports. The switch routes 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 28,
“Configuring IP Unicast Routing,” Chapter 31, “Configuring IP Multicast Routing,” and
Chapter 32, “Configuring MSDP.”
• Fallback bridging forwards traffic that the switch 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 33, “Configuring Fallback Bridging.”
Using Interface Configuration Mode
The switch supports these interface types:
• Physical ports—including switch ports and routed ports
• VLANs—switch virtual interfaces
• Port-channels—EtherChannel of interfaces
You can also configure a range of interfaces (see the “Configuring a Range of Interfaces” section on
page 9-8).
To configure a physical interface (port), enter interface configuration mode, and specify the interface type,
switch number, module number, and switch port number.
• Type—Fast Ethernet (fastethernet or fa) for 10/100 Mbps Ethernet or Gigabit Ethernet
(gigabitethernet or gi) for small form-factor pluggable (SFP) Gigabit Ethernet interfaces.
• Switch number—For the Catalyst 3750 Metro switch, this number is always 1.
Host A
SVI 1172.20.128.1 172.20.129.1SVI 2
Layer 3 switch
with routing enabled
VLAN 20
Host B
VLAN 30
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