Trouble shooting Missing VLAN

If you have checked your IP address setting and there is no issue found with IP address setting. But there is still no connectivity between devices in a VLAN, So the problem may be related to missing VLAN. To check the and verify the missing VLAN follow the steps.

Step 1

Issue the show vlan command in the switch privileged exec mode to check the port relationship with the expected VLAN. If the connected port has assigned to the different or wrong VLAN, use the switchport access vlan command to accurate the VLAN membership. Also, use the show mac address-table command to check which addresses were learned on a desired port of the switch.

The show mac address-table with interface Id will show VLAN that port is related. We can also display a complete mac address table using show mac address-table command. The example in Figure 1 shows MAC addresses on the F0/1 interface. Figure 2 display the complete mac address table of the switch.  You can also see in the image that mac address 000a.f37d.d3b8 has learned on interface Fast Ethernet interface 0/2 if this is not the expected VLAN number, change the port VLAN membership using the switchport access vlan command.

Step 2

If someone deletes the VLAN, the ports assigned to that VLAN become inactive. To check the VLAN use the show vlan command and you can also use the show interfaces switchport command.

Every port in a switch related to a VLAN, If the VLAN deleted, the member ports of this VLAN also becomes inactive and these ports cannot communicate with the rest of the network. Use the show interface f0/1 switchport command to check whether the port is active or inactive. The figure 3 shows the port with active and working VLAN and the Figure 4 show the switchport which VLAN is deleted. If the port is inactive, it is not functional until the missing VLAN is created again. For creating vlan use the vlan  vlan_id command.


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