12-5
Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-08
Chapter 12 Configuring Interface Characteristics
Interface Types
Switch Virtual Interfaces
A switch virtual interface (SVI) represents a VLAN of switch ports as one interface to the routing or
bridging function in the system. Only one SVI can be associated with a VLAN, but you need to configure
an SVI for a VLAN only when you wish to route between VLANs, to fallback-bridge nonroutable
protocols between VLANs, or to provide IP host connectivity to the switch. By default, an SVI is created
for the default VLAN (VLAN 1) to permit remote switch administration. Additional SVIs must be
explicitly configured.
Note You cannot delete interface VLAN 1.
SVIs provide IP host connectivity only to the system; in Layer 3 mode, you can configure routing across
SVI
s.
Although the switch stack or switch supports a total of 1005 VLANs (and SVIs), the interrelationship
be
tween the number of SVIs and routed ports and the number of other features being configured might
impact CPU performance because of hardware limitations. See the “Configuring Layer 3 Interfaces”
section on page 12-32 for information about what happens when hardware resource limitations are
reached.
SVIs are created the first time that you enter the vl
an interface configuration command for a VLAN
interface. The VLAN corresponds to the VLAN tag associated with data frames on an ISL or
IEEE 802.1Q encapsulated trunk or the VLAN ID configured for an access port. Configure a VLAN
i
nterface for each VLAN for which you want to route traffic, and assign it an IP address. For more
information, see the “Manually Assigning IP Information” section on page 3-15.
Note When you create an SVI, it does not become active until it is associated with a physical port.
SVIs support routing protocols and bridging configurations. For more information about configuring IP
ro
uting, see Chapter 40, “Configuring IP Unicast Routing,” Chapter 46, “Configuring IP Multicast
Routing,”and Chapter 48, “Configuring Fallback Bridging.”
Note The IP base feature set supports static routing and RIP. For more advanced routing or for fallback
bridging, enable the IP services feature set on the standalone switch or the stack master. For information
about using the software activation feature to install a software license for a specific feature set, see the
Cisco IOS Software Activation document.
SVI Autostate Exclude
The line state of an SVI with multiple ports on a VLAN is in the up state when it meets these conditions:
• The VLAN exists and is active in the VLAN database on the switch.
• The VLAN interface exists and is not administratively down.
• At least one Layer 2 (access or trunk) port exists, has a link in the up state on this VLAN, and is in
the spanning-tree forwarding state on the VLAN.
Note The protocol link state for VLAN interfaces come up when the first switchport belonging to the
corresponding VLAN link comes up and is in STP forwarding state.
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