cat2960 native vlan tagged on trunk

[fsoffia]

hello,

why cat2960 tags native vlan 1 on 802.1q trunks ?

I know that 802.1q does not tag native vlan.

Is there a way to UNtag the native vlan on cat2960 ?

best regards

francesco

[ankbhasi]

Hi Francesco,

2960 does not have the capability of tagging native vlan although this feature is avaiable on cat6500. By default native vlan is 1 but if native vlan is changed vlan 1 will be sent as tag on the trunk link.

Can you paste the output of "sh interface switchport"?

Regards,

Ankur

[fsoffia]

hi Ankur,

hear "sh int..." from cat2960

you can see that native vlan 1 is tagged !

Switch#sh interfaces f0/1 switchport

Name: Fa0/1

Switchport: Enabled

Administrative Mode: trunk

Operational Mode: trunk

Administrative Trunking Encapsulation: dot1q

Operational Trunking Encapsulation: dot1q

Negotiation of Trunking: On

Access Mode VLAN: 1 (default)

Trunking Native Mode VLAN: 1 (default)

Administrative Native VLAN tagging: enabled

Voice VLAN: none

Administrative private-vlan host-association: none

Administrative private-vlan mapping: none

Administrative private-vlan trunk native VLAN: none

Administrative private-vlan trunk Native VLAN tagging: enabled

Administrative private-vlan trunk encapsulation: dot1q

Administrative private-vlan trunk normal VLANs: none

Administrative private-vlan trunk private VLANs: none

Operational private-vlan: none

Trunking VLANs Enabled: ALL

Pruning VLANs Enabled: 2-1001

Capture Mode Disabled

Capture VLANs Allowed: ALL

Protected: false

Unknown unicast blocked: disabled

Unknown multicast blocked: disabled

Appliance trust: none

Switch#

Switch#sh ver

Cisco IOS Software, C2960 Software (C2960-LANBASE-M), Version 12.2(25)SEE2, RELEASE SOFTWARE (fc1)

Copyright (c) 1986-2006 by Cisco Systems, Inc.

Compiled Fri 28-Jul-06 04:33 by yenanh

Image text-base: 0x00003000, data-base: 0x00AA2F34

francesco

[fsoffia]

hi Ankur,

I posted the "sh interface f0/1 switchport" output.

I didn't have your response about the output.

I paste it again.

I'm wrong in thinking that NATIVE VLAN IS TAGGED on trunks ?

Switch#sh interfaces f0/1 switchport

Name: Fa0/1

Switchport: Enabled

Administrative Mode: trunk

Operational Mode: trunk

Administrative Trunking Encapsulation: dot1q

Operational Trunking Encapsulation: dot1q

Negotiation of Trunking: On

Access Mode VLAN: 1 (default)

Trunking Native Mode VLAN: 1 (default)

Administrative Native VLAN tagging: enabled

best regards

francesco

[Kevin Dorrell]

I don't know if it will work, but try no switchport trunk native vlan tag

Kevin Dorrell

Luxembourg

[fsoffia]

it does not work

[Kevin Dorrell]

At this stage, I wonder if it just the diagnostic output that is at fault.

Have you tried sniffing to see if the native VLAN really is tagged?

Kevin Dorrell

Luxembourg

[fsoffia]

no I don't try sniffing, it's not simple on a trunk...

We had some problems with intervlan routing using cat2960 that we never had before using cat2950...

It's the cat2960 output:

Trunking Native Mode VLAN: 1 (default)

Administrative Native VLAN tagging: enabled

that make me thinking that there is a difference in cat2960 TRUNK behaviour.

What do you think ?

francesco

best regards

[ankbhasi]

Hi Francesco,

Give me sometime may be a day or 2 I will update you sure on the same. Incase if someone replies with correct statement well and good incase not I will provide you with the information soon.

Regards,

Ankur

[fsoffia]

thanks Ankur

francesco

[nambi_gct]

Hi,

Can you please check if this command is available in your switch.

"show vlan dot1q tag native"

If so, I think you can use "no vlan dot1q tag native" in the global configuration mode to disable native vlan tagging.Please give a try.Not sure if it works.

Regards,

Nambi.

[fsoffia]

hi Nambi

command not supported...

thanks

francesco

[ankbhasi]

Hi Francesco,

I got the information on the output what you see. Actually that is a bogus output and will always show you as "enable" no matter if you tag or untag native vlan.

Bydefault your native vlan data will always pass through the trunk as untagg even if you see the output of "show interface switchport" command as "Administrative Native VLAN tagging:enabled".

If you issue a command "vlan dot1q tag native" it will tag the data for native vlan on all trunk and if you issue a command "no vlan dot1q tag native" it will send the data for native vlan as untagg on all trunks. As of now this feature is no available per interface and is the reason the output of "sh int switchport" will always show you as "Administrative Native VLAN tagging:enabled".

So you can just ignore that output and check the status of "show vlan dot1q tag native" if it shows you enable this means native vlan is tag and if you see disable this means native vlan is not tagged.

HTH

Ankur

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[fsoffia]

hi Ankur, thanks.

Now I understand that the output "Administrative Native VLAN tagging:enabled" does not show the actual status of vlan tagging about native vlan.

BUT

The command "vlan dot1q tag native" is not supported in global or interface config modes...

The command "show vlan dot1q tag native" is not supported...

I have this IOS version running:

Switch#sh ver

Cisco IOS Software, C2960 Software (C2960-LANBASEK9-M), Version 12.2(40)SE, RELEASE SOFTWARE (fc3)

What I have to think ?

That native 802.1q vlan at the moment is ALWAYS UNTAGGED ?

Thankyou in advance for a "last response" from you, I'll rate that...

best regards

francesco

[ankbhasi · Accepted solution]

Hi Francesco,

Yes this command is not supported on 2960 as of now because 2960 does not support the feature of tagging native vlan. This command is available on switches like 3560 , 3750 and above.

At the moment native vlan is ALWAYS UNTAGGED on 2960 switch. But because the output format structure of show commands are common for most of the IOS platform switches and that is the reason we see this output in "sh interface switchport" command but that is a bogus information and should be ignored.

HTH

Ankur

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