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How do I change the native vlan on a LACP member port? Seeing CDP Native VLAN Mismatch.

mattybrownuk
Level 1
Level 1

I've connected two L3 switches, which each has a different default VLAN.  I've used two interfaces, grouped into a port-channel/LAG, for redundancy and to increase available bandwidth between the two.

The configuration is identical on the two switches:

interface gigabitethernet25
 description "SHDS connection"
 spanning-tree link-type point-to-point
 channel-group 1 mode auto
!
interface gigabitethernet26
 description "SHDS connection"
 spanning-tree link-type point-to-point
 channel-group 1 mode auto
!
interface Port-channel1
 description "SHDS connection"
 spanning-tree link-type point-to-point
 switchport trunk allowed vlan add 2,11
 switchport trunk native vlan 99
 no macro auto smartport
!

The native VLAN for the port-channel is set to vlan 99 both sides.  Because the native vlan is taking on that of the default vlan on gi25 and gi26, I'm seeing CDP warnings, such as: "%CDP-W-NATIVE_VLAN_MISMATCH: Native VLAN mismatch detected on interface gi26."... which isn't causing me any issues, as far as I can see, but the warnings are very annoying when trying to configure the switches via the CLI.

When I attempt to change the native VLAN on one of the LAG member ports, I see the error: "Port gi25 belongs to a port-channel.".

What could I have done differently?  Can I fix this?  Perhaps I should be looking into turning off CDP on these ports, since it seems to be of no consequence?

Any help much appreciated!

Matty Brown.

11 Replies 11

John Blakley
VIP Alumni
VIP Alumni

Your physical ports need to have the same configuration as the virtual interface:

interface gigabitethernet25
description "SHDS connection"
spanning-tree link-type point-to-point

switchport trunk allowed vlan add 2,11
switchport trunk native vlan 99

 channel-group 1 mode auto
!
interface gigabitethernet26
description "SHDS connection"
spanning-tree link-type point-to-point

switchport trunk allowed vlan add 2,11
switchport trunk native vlan 99


channel-group 1 mode auto
!
interface Port-channel1
description "SHDS connection"
spanning-tree link-type point-to-point
switchport trunk allowed vlan add 2,11
switchport trunk native vlan 99
no macro auto smartport

 

You may have to shut the po1 interface down along with both of the physicals before adding the config.

HTH,

John

HTH, John *** Please rate all useful posts ***

Hi John.  Your solution sounds spot on... only the switches aren't playing ball.

Shutting down the ports and port-channel isn't enough to change the VLAN membership of port-channel members - they can't be members at all.

I tried removing the ports from the port-channel, changing the VLAN membership, then re-adding the ports to the port-channel, but I get this message:

Port gi25 belongs to a VLAN.

So given that I can't change the native VLAN, or seemingly anything to do with VLAN membership on a port-channel member, how am I to resolve this native VLAN mismatch?

Matty.

Try this:

1. Shut down the po1 interface.

2. default the two interfaces that you want to be part of the group - this will clear the interface configs.

3. If you still have po1, remove that interface - no int po1

4. Then start over with readding the configs

 

Get an outage window if there's live traffic before doing this. :) 

HTH,

John

HTH, John *** Please rate all useful posts ***

I'm very tempted to download the startup config, edit it, upload it and reboot.  I don't really understand why the switch is refusing to accept the commands you suggested.

By the way, do you know what the command is to wipe the config on a port, to save me doing loads of no commands?

Thanks,

Matty.

Matty,

You made mention of the SG series switch above. I'm not sure how to default the port, but on normal IOS (which I believe the SG uses VXWorks), you would do "default int <interface>"

HTH,
John

HTH, John *** Please rate all useful posts ***

There doesn't appear to be a way of defaulting the configuration on an interface on the SG300.  :(.

Hello

Layer2 etherchannel

 

1) default the physical interfaces and shut them down

2) remove the old port-channel

3) on the physical interfaces apply ONLY the channel-group info( this will auto create the logical port channel interface

4) on the port channel interface apply the L2 config

switchport trunk encapsulate dot1q

swichport. mode  trunk

switchport trunk native vlan xxx

 

5) enable the physical interfaces

 

Note: make sure the native vlan is applicable to both side of the etherchannel as its link specific

res

paul

 


Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul

Downloading, modifying and uploading the startup config doesn't work... it was a long shot anyways, but it still results in the same error message... just it occurs during loading of the startup-config.

Matty

I'm not sure I understand the problem you are describing and I don't know what switches you are using but you need to tell the ports they are trunks ie. in your original configuration your ports are access ports as far as I can see.

I can't see the command "switchport mode trunk" anywhere, either on the individual ports or the port channel interface.

So do you have the option to add this command ?

If so add it to the physical and port channel interfaces.

Jon

 

Hi Jon

Our switches are Cisco Small Business SG300-28.  All ports are trunks by default.  I could add the switchport mode trunk command... Not sure if it'll help though, but at this point, I'll give anything a go.

I'll post back tomorrow and let you know if it made any difference.

Thanks,

Matty.

amikat
Level 7
Level 7

Hi,

The Small Business Switches handle LAG configuration in slightly different way than Catalysts and therefore my view is that the suggestions here are not really pertinent to the 300 Series.

If you can afford to play with the switches you may try the following procedure:

Configure vlan 99 as default vlan via the "default-vlan vlan 99" command under the "vlan database", write to memory and reload. Then configure your port-channel interface (no need to specify the native vlan) and add LAG members. CDP should stay silent.

Good Luck!

Best regards,

Antonin

 

 

 

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