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VLAN interface not reachable TIP


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Today I experienced a odd issue that I wanted to share.

I have a VLAN interface 101 created with an IP address assigned. I have switchports assigned to the VLAN but the interface shows down/down when the command show interface VLAN 101.


So I checked the arp table to see if there is a conflict with an IP address for the VLAN management IP and no IP addresses were found for VLAN101. Ahhh....

The issue turned out to be related to no devices being on that VLAN currently, the VLAN interface is not available. Once a machine was present on that VLAN, the interface automatically changed from down/down to up/up and everything was working. They unplug that workstation and no devices are in VLAN101, then the interface goes back to down/down status.

I found this interesting and wanted to share. Many people will monitor the switch using the VLAN interface which would show down but in actuality the switch is still up. My suggestion is to pick a VLAN that the router is plugged into (like the transit VLAN).

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