NATIVE_VLAN_MISMATCH on switchports configured as access

[tato386]

I need to connect a Cisco 2900 switch with a fiber port to a second Cisco 2900 that does not have any fiber ports.  In order to not spend any money on transceivers/GBIC or any other converter type device I am using a third 3700 switch that has both types of ports as a big and expensive transceiver.  Here is what I did:

Both Cisco 2900 switches are pretty much default config with no VLANs configured.  The 3700 does have several VLANs and trunks configured and I would like to keep traffic on the 2900's segregated from the 3700's VLANs.

On the 3700 switch I took a fiber port and a copper port and made them access ports like this:

int gig3/0/44
switchport mode access
switchport access vlan 4455

int gig3/0/50
switchport mode access
switchport access vlan 4455

The config basically works and the two 2900's seem to be talking to each other well.  But when I do "show CDP neighbor detail" and "show logging" on the 3700 I see the native VLAN mismatch errors on those two ports. I thought that by making these two ports access the fact that they are configured for VLAN4455 would be transparent to the 2900's.  Should I worry about this error?  I would like to get rid of it.  What are my options here?

Thanks,
Diego

[jimmysands73_2]

Have you wiggled the cable?

[glen.grant]

  It won't hurt anything it's just a informational message saying the vlan on the other end doesn't match . The only way would be to match  the vlan on the 2900 which probably doesn't even allow you to configure a vlan that high or turn off cdp between the switches .   That's a normal message but does not hurt anything.

[Rolf Fischer · Accepted solution]

Hi Diego,

CDPv2 exchanges Native-VLAN information with a TLV:

http://www.rhyshaden.com/cdp.htm

I would like to get rid of it.  What are my options here?

I'm not aware of a way to disable this particular TLV but you could

- configure a logging discriminator to suppress this type of syslog message

- disable CDP on a per-interface basis

- enable CDPv1 on a per-interface globally (by disabling v2)

Feel free to ask further!

Regards

Rolf

[tato386]

I think I will just have to train myself to live with it.

Thanks to all.

Rgds,

Diego

[Rolf Fischer]

Hi Diego,

if you want to get rid of this type of syslog messages, you can configure a logging discriminator (if your IOS supports it):

logging discriminator NVM mnemonics drops NATIVE_VLAN_MISMATCH
logging buffered discriminator NVM
logging console discriminator NVM
[...]
#show logging
 Console logging: level debugging, 37 messages logged, xml disabled,
 filtering disabled, discriminator(NVM),
 0 messages rate-limited, 71 messages dropped-by-MD
Buffer logging:  level debugging, 37 messages logged, xml disabled,
filtering disabled, discriminator(NVM),
 0 messages rate-limited, 71 messages dropped-by-MD

Hope that helps

Rolf

[tato386]

Rolf,

If I can't train myself to ignore the error your suggestion is certainly a good one!

Thanks again,

Diego