VLAN MISMATCH ON 1841

[okoroji80]

Dear Support Team,

i have a LAN setup with the following connection:

HWIC Card on Cisco 1841 connected to Cisco 2960 switch.

the config on the HWIC card is such that the 4 interfaces on the Card are made to access vlan 10.

thus am having the following error'' 

*Dec 21 12:56:34.559: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/0/2 (10), with Switch FastEthernet0/22 (1).

Note the Link B/W the HWIC and Cisco 2960 is not a trunk link just a normal cable connection.

how can the above be resolved without having to trunk either the switch or the hwic interfaces ?

[Jon Marshall]

Jude

Is the switchport on the 2960 in vlan 10 ?

Can you post config of 2960 switch and the 1841 ?

Jon

[Richard Burts]

It is my understanding of the message that router interface FastEth0/0/2 is connected to switch port Fast0/22 and that while the router interface is assigned to vlan 10 the switch port is still in its default of vlan 1.

The way to fix this is to either change the vlan of the router interface to vlan 1 or to change the switch port to vlan 10 (assuming that vlan 10 has been created on the switch).

HTH

Rick

[okoroji80]

The  Cisco 2960 switch is in its default config.

with vlan1 as its native vlan.

Note also that the Fa0/0/2 is an Hwic card sloted on the router.

i have tried using Vlan 1 on the router and that did not work, as i made the four ports on the hwic card an accesss ports.

accessing vlan 1 and this did not work

@ Mr. Richard

I have setup Vlan 10 on the 2960

Are you suggesting that int Fa0/22, to be setup as : Swithcport access vlan 10 ?

[Jon Marshall]

Jude

Are you suggesting that int Fa0/22, to be setup as : Swithcport access vlan 10 ?

Both ends of the link should match. If you do not put fa0/22 into vlan 10 then you have joined vlan 1 and vlan 10 together and that is not a good thing to do.

This is what the message is telling you ie. each of the link thinks it is in a different vlan so the switch thinks any frames received on it's port are in vlan 1 and the router thinks any frames received on it's port are in vlan 10.

Jon

[okoroji80]

Noted Jon.

But do i have to trunk but ends ( Fa0/22 and  Fa0/0/2 )

or just to make fa0/22: switchport access vlan 10  ? or switchport native vlan 10

[joshuacmoore]

Turn off CDP if you don't like the message. Nothing is wrong with your config. The message is for informational purposes.

Sent from Cisco Technical Support iPhone App

[Richard Burts]

I disagree that this is just an informational message. It is true that if you turn off CDP that you will no longer receive the message. But that does not mean that there is not still a problem.

Recently I was involved in solving a problem where a switch port kept going into error disable. After some investigation we found that the port was going into error disable because it was receiving its own Spanning Tree BPDU. After a bunch of troubleshooting we found a situation, several devices away in the network. The situation was very much like what Jude has where there was a vlan mismatch between two devices. The link between these devices really did create a layer 2 loop. We were running Spanning Tree but Spanning Tree did not detect the loop. The reason was that the device which had vlan 10 was receiving a BPDU associated with vlan 1, and the vlan 1 device was receiving a BPDU associated with vlan 10. So they did not detect the loop.

So I certainly agree with Jon that Jude needs to fix this and to make both devices agree on which vlan this connection belongs to. Either both devices need to make it vlan 1 or both devices need to make it vlan 10.

HTH

Rick

[joshuacmoore]

I agree... To an extent. We also don't know that the original poster has any intentions of running a topology where spanning tree is necessary. It sounded to me that he simply wanted to hook up a 2960 switch to the WIC card unmanaged with all ports untagged. In this case, there's no reason to worry about "native" VLAN to begin with.

Sent from Cisco Technical Support iPhone App

[okoroji80]

Correct an just trying to hook up a 2960 SWITCH to the WIC card of 1841 Router so as to give internet access to my LAN network . that is all i want to achieve.

[Jon Marshall]

Jude

It's up to you whether you turn off the message or just fix the problem. In this instance Joshua is correct in that it makes no difference although as Rick pointed out in large switched networks it most certainly can.

i have tried using Vlan 1 on the router and that did not work, as i made the four ports on the hwic card an accesss ports.

Can you explain what you mean by the above ?

Jon

[okoroji80]

The statement '' i have tried using Vlan 1 on the router and that did not work, as i made the four ports on the hwic card an accesss ports. ''

What the statement above means is : I made vlan1 an SVI such that i will have thesame vlan on the 2960 and on 1841 hwic card but this did not yield any result.

the PCs connected to the hwic were able to get ip via DHCP on the router but could not connect to the internet. thus i resorted to the use of VLAN 10.

[Jon Marshall]

Jude

the PCs connected to the hwic were able to get ip via DHCP on the router but could not connect to the internet. thus i resorted to the use of VLAN 10.

And did it work using vlan 10 ?

Edit - if not can you post your 1841 config.

Jon

[daniel.dib]

I agree with Jon and Richard here.

You essentially bridged two different VLANs together. People often believe that CDP is the protocol that is detecting misconfigurations and that this information is purely informational. However, misconfiguration of native VLAN is detected by looking at the BPDUs and the incoming frames. CDP is used to carry this information.

While you do seem to have a simple setup now that's not really a reason for not doing things properly. Temporary fixes often become permanent ones and then the network grows and then people hook things up that weren't intended and you have a loop in the network.

Daniel Dib
CCIE #37149

Please rate helpful posts.

[okoroji80]

... Yes it worked using Vlan 10