Switch Virtual Interfaces, or SVIs on Cisco IOS use a feature called autostate to determine the interface availability. By default an SVI will show an up/down (Status / Protocol) for an SVI unless it’s VLAN exists in the VLAN database and there is one switch port, either trunk or access, in that VLAN not only in an up/up state but also not blocked by spanning tree. So if you were to simply turn up an SVI with an IP address, that interface would not be reachable until those conditions are met. For more information reference the Understanding SVI Autostate Exclude section of this document.
Switch(config)# vlan 100 Switch(config-vlan)# interface vlan100 Switch(config-if)# ip address 192.168.100.1 255.255.255.0 Switch(config-if)# end Switch# show ip interface brief | exclude unassigned Interface IP-Address OK? Method Status Protocol Vlan100 192.168.100.1 YES manual up down Switch(config)# interface fa0/1 Switch(config-if)# switchport access vlan 100 Switch(config-if)# LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan100, changed state to up
In most situations this is the desired result, but there may be cases where you wish to override this behavior. On some platforms Cisco includes the (undocumented last I checked…) option to disable the autostate feature with the vlan interface command no autostate. This disables the autostate calculation and makes the SVI interface permanently active. Unfortunately, I’ve yet to see this available on anything but routers. Another option allows you to remove individual ports from the autostate calculation using the switchport autostate exclude interface configuration command.
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