Troubleshoot Switch Virtual Interfaces (SVI)

Exam: Cisco 642-832 - Troubleshooting and Maintaining Cisco IP Networks (TSHOOT v1.0)

SVI or Switched Virtual Interface (commonly known is VLAN interface) is used if you want a layer 3 interface for a VLAN. The most common use of SVI is for inter-vlan routing or to get a manageable IP for a layer 2 switch.

SVI is created by using the "interface VLAN [VLAN NUMBER]" command. Although SVI creation is very simple and in most cases, the SVI comes up without any issues but there are times when SVI shows up/down state in the "show ip int brief" output.Following are most common cases when troubleshooting SVI in up/down state:

• Make sure that the VLAN this SVI represents exists in the VLAN database. So, if you are creating an SVI for vlan 10, make sure that you have already created that VLAN.
• SVI has a feature called "autostate" that is enabled by default. This feature is used to bring the SVI up automatically as long as there is at least one interface in that VLAN and at least one interface is up/up. So, if an SVI is not coming up, make sure that a functional port exists in that VLAN.
• Sometimes, you just want to bring the SVI up without having any functional interface in the VLAN. For instance, you want to manage a switch through SVI but there is no access port needed on the switch for that VLAN (as it will pass through the trunk). In this case, make sure, that the SVI vlan is allowed through the trunk.

Of course, if an SVI is in down/down state, make sure that the interface has been enabled by "no shutdown".