erro NATIVE_VLAN_MISMATCH

[mateus_guilherme]

Hi I would like to understand why I am receiving the following message on switches SW2 and SW3:

%CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/1 (5), with Switch FastEthernet0/2 (1).

The Fa01 port of switch SW2 is configured in access mode (VLAN5) and switch SW3 has no vlan configuration (the SW3 switch has no configuration, I would like it to behave like a dumb switch).

The packets generated by the IPC002 and IPC001 machines must circulate through the SW3 switch without a vlan tag and when they enter the SW2 switch through the Fa01 port, they receive the vlan 5 tag.

the communication of the IPC001 and IPC002 computers is working perfectly, but I would like to understand the reason for this message.

thank you

[balaji.bandi]

Why not configure both the side Trunk to pass all the VLAN you looking to achieve , is that works ?

[Richard Burts · Accepted solution]

The original poster tells us that this implementation is working and asks why he is receiving the message. Connectivity is working as expected and we should recognize that this is more an informational message than it is an error message. The message is generated by CDP which is monitoring information exchanged between the switches.

We are told that the connection is over access ports. The access port in one switch is configured to be in vlan 5. The other access port is on a switch which has no vlan configuration. But that does not mean that there is no vlan. With no vlan configuration by default all ports are access ports in vlan 1. So the port on SW2 in vlan 5 is receiving an Ethernet frame which originated in vlan 1. In terms of forwarding this frame the vlan mismatch does not matter, and the frame is forwarded just fine. But as CDP exchanges information between the switches it notices that the connection is vlan 5 on one side but is vlan 1 on the other side and it generates an informational message.

The easy way to make the message stop would be to configure the port on SW3 to be in vlan 5. But the original poster tells us he wants to operate SW3 like a dumb switch. But SW3 is not quite a dumb switch - it runs CDP. So probably the best thing is to just accept that this message will be generated.

[Richard Burts]

I am glad that my explanation was helpful. Thank you for marking this question as solved. This will help other participants in the community to identify discussions which have helpful information. This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.

[mlund]

Hi

Richard has given you an excellent answer. Just to add, you can disable cdp in one end, to get rid of the message

/Mikael

[Joseph W. Doherty]

"Just to add, you can disable cdp in one end, to get rid of the message"

Also to add, you may have the choice to disable CDP globally or on just the "problem" interface.