NATIVE_VLAN_MISMATCH

[bpub]

Hello,

been getting a message that says NATIVE VLAN MISMATCH discovered on SWITCH B GI1/0/46 (207). , with Switch A Gi0/3 (1). 

so i see switch A has a trunk on port 3 allowing 1-207,209-769,772-4094

and switch B has vlan 207 on port 46. 

If vlan 2

[bpub]

if vlan 207 is allowed how come i'm getting vlan mismatch

[Joseph W. Doherty]

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@bpub wrote:

if vlan 207 is allowed how come i'm getting vlan mismatch

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Because the error is a native VLAN mismatch, not the same thing as whether the VLAN is allowed or not.

The native VLAN defines a trunk VLAN whose frames will be transmitted without a VLAN tag and which VLAN a trunk's untagged received frames will be directed to.

Since Cisco trunks can generate/receive untagged VLAN frames, both sides should agree on what that VLAN is.  You can "jump" VLAN, on a trunk, using mismatched VLANs (much as you could do with non-trunk access ports assigned different VLANs), but this is generally due to a misconfiguration.  CDP, though, compares sides for these two inconsistences, and throws an error for a mismatch.

[liviu.gheorghe]

Hello @bpub ,

check the both ends of the trunk have the same command switchport trunk native vlan x

HTH

[bpub]

Yes, thank you. one end was a vlan and the other was a trunk. I changed one end to trunk and allowed same vlans and message went away. 

Thank you!

[nict]

Hi @bpub 

You have configured Native Vlan for Switch B to be 207. On Switch A you are using the default Native Vlan 1.

NATIVE VLAN MISMATCH discovered on SWITCH B GI1/0/46 (207). , with Switch A Gi0/3 (1)

If you want to use Vlan 207 as Native Vlan, go use this command on Switch A Gi0/3:

switchport trunk native vlan 207

[David Ruess]

Among the answers of "it must be the same on both sides" you may want to look at your configuration as well. You're allowing some VLAN's on the trunk of SW-A but not on SW-B so they would be denied. Unless I am reading that wrong it read that youre allowing 1-207,209-769,772-4094  on SW-A and only allowing 207 on SW-B.

[Joseph W. Doherty]

Both switches defined as trunk ports?

Both switches defined to use the same VLAN as the native VLAN (which is VLAN 1, by default)?

[bpub]

thank you, yes only one side was trunk for some reason. made both ends trunks and allowed same vlans and issue was fixed. 

appreciate your help.

[Joseph W. Doherty]

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@bpub wrote:

thank you, yes only one side was trunk for some reason. made both ends trunks and allowed same vlans and issue was fixed. 

appreciate your help.

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Thank you for letting us know what the issue was, and, of course, you were able to resolve it too.