Configure the Native VLAN on Both Side Of The Trunk

Be sure to remember to configure the native VLAN on both sides of the trunk link or you will get this error until you do so (or disable CDP):

*Mar  1 01:35:01: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/13 (1), with sw1 FastEthernet0/13 (10).

They come in once every minute (CDP updates go every 60 seconds by default):

*Mar  1 01:38:01: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/13 (1), with sw1 FastEthernet0/13 (10).
*Mar  1 01:39:01: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/13 (1), with sw1 FastEthernet0/13 (10).
*Mar  1 01:40:01: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/13 (1), with sw1 FastEthernet0/13 (10).

sw2(config-if)#do sh cdp
Global CDP information:
        Sending CDP packets every 60 seconds
        Sending a holdtime value of 180 seconds
        Sending CDPv2 advertisements is  enabled

What happens if you disable CDP?  Will you still get the error?

sw1:
sw1(config)#do sh run int fa0/13
Building configuration…

Current configuration : 128 bytes
!
interface FastEthernet0/13
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 10
 switchport mode trunk
end

sw2:
sw2(config-if)#do sh run int fa0/13
Building configuration…

Current configuration : 110 bytes
!
interface FastEthernet0/13
 switchport trunk encapsulation dot1q
 switchport mode trunk
 no cdp enableend

***
sw1#sh int fa0/13 trunk

Port        Mode         Encapsulation  Status        Native vlan
Fa0/13      on           802.1q         trunking      10

sw1#sh int fa0/13 switch | i Native VLAN
Administrative Native VLAN tagging: enabled

sw1#sh cdp int fa0/13
FastEthernet0/13 is up, line protocol is up
  Encapsulation ARPA
  Sending CDP packets every 60 seconds  Holdtime is 180 seconds

sw2#sh int fa0/13 trunk

Port        Mode         Encapsulation  Status        Native vlan
Fa0/13      on           802.1q         trunking      1

sw2#sh int fa0/13 switch | i Native VLAN
Administrative Native VLAN tagging: enabled

sw2#sh cdp int fa0/13
[Note: No output because we've disabled CDP]sw2#

It’s been a few minutes and no alarms(on either switch):

*Mar  1 01:42:14: %SYS-5-CONFIG_I: Configured from console by console
sw1#sh clo
*01:48:09.468 UTC Mon Mar 1 1993

*Mar  1 01:41:51: %SYS-5-CONFIG_I: Configured from console by console
sw2#sh clo
*01:45:09.826 UTC Mon Mar 1 1993

Another good reason to run CDP.