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Native VLAN Mismatches.

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Error#1

Lets assume that one of the workstations on the network (PC 5) cannot connect to the internal web server WEB/TFTP, lets use the figure below as an example of a switched network, the first place you start will be at the Switch 2 to check if VLANs are properly configured. Looking at the diagram, switch port fa0/3 on Switch 2 is configured as a trunk port. 

Oct 27 12:16:29.352 EET: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet2/6 (2), with sw-el0 GigabitEthernet0/8 (1).

  When you connect to switch S2, if there is an error on the switch port, it will appear on your console window, in this case there is and it looks like this:

        S2#
        #CDP-4-NATIVE VLAN_MISMATCH: Native VLAN mismatch discovered on
         FastEthernet0/3  (100), with S1  FastEthernet0/3  (99).


Using the show interfaces fa0/3 switchport command will display connectivity detail on the port.

e.g

        S2# show interfaces fa0/3 switchport
        Name:  fa0/3
        Switchport:  Enabled
        Administrative Mode:  trunk
        Operational Mode:  trunk
        Administrative Trunking Encapsulation:  dot1q
        Operational Trunking Encapsulation:  dot1q
        Nagotiation of Trunking:  On
        Access Mode VLAN:  1 (default)
        Trunking Native Mode VLAN: 100 (Inactive)
        …
        Trunking VLANs Enabled:  10,  99

                              …

Looking at the above detail, you will notice that the native VLAN has been set to VLAN 100 and it is inactive.
 As you look further down the output, you see that the allowed VLANs are 10 and 99.
To sum it up, this is a case of a mismatched native VLAN



The solution:

 You need to reconfigure the native VLAN on the Fast Ethernet F0/3 trunk port to be VLAN 99.  e.g


    S2#config t
    S2#interface fa0/3
    S2#switchport trunk native vlan 99
    S2#end
    

After you have done that, use the show interfaces fa0/3 switchport confirm you configuration.

And use the Ping to confirm connectivity with the server.  e.g.

    PC5> ping 192.168.10.30
    Pinging 192.168.10.30 with 32 bytes of data:
    Reply from 192.168.10.30: bytes-32 times-147ms TT-128
    Reply from 192.168.10.30: bytes-32 times-147ms TT-128
    Reply from 192.168.10.30: bytes-32 times-147ms TT-128
    ...

 The screen output for the computer PC5 shows that connectivity has been restored to the WEB/TFTP server found at IP address 192.168.10.30.

This Article has been taken from http://www.orbit-computer-solutions.com/Native-VLAN-Mismatches.php
When you connect to switch S2, if there is an error on the switch port, it will appear on your console window, in this case there is and it looks like this:
S2#
#CDP-4-NATIVE VLAN_MISMATCH: Native VLAN mismatch discovered on
 FastEthernet0/3  (100), with S1  FastEthernet0/3  (99).
 
Using the show interfaces fa0/3 switchport command will display connectivity detail on the port.
 
e.g
S2# show interfaces fa0/3 switchport
Name:  fa0/3
Switchport:  Enabled
Administrative Mode:  trunk
Operational Mode:  trunk
Administrative Trunking Encapsulation:  dot1q
Operational Trunking Encapsulation:  dot1q
Nagotiation of Trunking:  On
Access Mode VLAN:  1 (default)
Trunking Native Mode VLAN: 100 (Inactive)
…
Trunking VLANs Enabled:  10,  99
                              …
 
Looking at the above detail, you will notice that the native VLAN has been set to VLAN 100 and it is inactive.
 As you look further down the output, you see that the allowed VLANs are 10 and 99.
To sum it up, this is a case of a mismatched native VLAN
 
 
 

The solution:

 
 You need to reconfigure the native VLAN on the Fast Ethernet F0/3 trunk port to be VLAN 99.  e.g
 
S2#config t
S2#interface fa0/3
S2#switchport trunk native vlan 99
S2#end
 
After you have done that, use the show interfaces fa0/3 switchport confirm you configuration.
And use the Ping to confirm connectivity with the server.  e.g.
PC5> ping 192.168.10.30
Pinging 192.168.10.30 with 32 bytes of data:
Reply from 192.168.10.30: bytes-32 times-147ms TT-128
Reply from 192.168.10.30: bytes-32 times-147ms TT-128
Reply from 192.168.10.30: bytes-32 times-147ms TT-128
...
 The screen output for the computer PC5 shows that connectivity has been restored to the WEB/TFTP server found at IP address 192.168.10.30.
- See more at: http://www.orbit-computer-solutions.com/Native-VLAN-Mismatches.php#sthash.nYrDvqdI.dpuf
Error#1
Lets assume that one of the workstations on the network (PC 5) cannot connect to the internal web server WEB/TFTP, lets use the figure below as an example of a switched network, the first place you start will be at the Switch 2 to check if VLANs are properly configured. Looking at the diagram, switch port fa0/3 on Switch 2 is configured as a trunk port.     
- See more at: http://www.orbit-computer-solutions.com/Native-VLAN-Mismatches.php#sthash.nYrDvqdI.dpuf
Error#1
Lets assume that one of the workstations on the network (PC 5) cannot connect to the internal web server WEB/TFTP, lets use the figure below as an example of a switched network, the first place you start will be at the Switch 2 to check if VLANs are properly configured. Looking at the diagram, switch port fa0/3 on Switch 2 is configured as a trunk port.     
- See more at: http://www.orbit-computer-solutions.com/Native-VLAN-Mismatches.php#sthash.nYrDvqdI.dpuf

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