SVI is down after moving the trunk link from one switch to another

[gurbinder.kabbay]

Hi Experts

I have a very strange experience in which I moved the trunk link from one switch to another and this movement of cable is making SVI down/down.

Connectivity like below:

Current Connectivity: Switch A<------trunk vlan 100--------->Switch B

New Connectivity : Switch C<--------Trunk vlan100----------> Switch B

I am not doing any change on Switch B. I am only changing the physical connectivity and doing config on left hand switch C. but it is making the SVi down on the Switch B. When I am again connecting the cable to SwitchA on left hand side switch, the SVI will come up on Switch B.

I tried all the basic troubleshooting  like check L2 Vlans in database, Trunk port has allwoed vlan, physical connectivity. but still the issue is same.

Can someone please help on this.

Regards,

Gurbinder

[Reza Sharifi]

Hi,

For Switch  C, can you make sure that the VTP mode is in transparent or off?

Also, can you post "sh run" from both switch A and switch C?

HTH

[Flavio Miranda]

Hi,

 Hard to say anything without seing any config or logs, switch model, version, etc.  This can be a bug but can also be some misconfiguration.

 Can you share config from switch C and B ?

[MHM Cisco World]

SWB is transit SW, i.e it dont have access port assign to this VLAN 
the VLAN is allow in trunk and hence it SVI is UP.
try do 
vlan x <<-
no auto state <<- 

[Richard Burts]

I agree that seeing the config from the switches would be good. It would also be helpful if you would post the output from both switch B and switch C of the command show interface trunk while the connection is using switch C.

[paul driver]

Hello
Make sure switch C is not enabled for routing and the trunk (C) side is allowing vlan 100 over it and it has vlan 100 in the vlan database.

Example switch C
conf t
no ip routing
vlan 100
exit
int x/x
description trunk to B
switchport trunk allowed vlan 100

[gurbinder.kabbay]

Hi Experts

Connectivity like below:

Current Connectivity: Switch A<------trunk vlan 100--------->Switch B

New Connectivity : Switch C<--------Trunk vlan100----------> Switch B

Switch A config: 6509-E, layer 3 SVI created on it

int xx/xx

switchport

switchport trunk encapsulation dot1q

switch trunk native vlan 999

switch port trunk allowed vlan 10

end

Switch B config: 6509-E, layer 3 SVI created on it

int xx/xx

switchport

switch trunk native vlan 999

switch port trunk allowed vlan 10

end

Switch C config: N9K-C93360YC, layer 3 SVI created on it

int xx/xx

switchport

switch trunk native vlan 999

switch port trunk allowed vlan 10

end

In addition to above info, when we initial tried to shift the connectivity of A-->B to C-->B , then on C switch side port was err-disable state, but even after reset it was not working.

Any idea please ?

Regards

Gurbinder

[MHM Cisco World]

Switch C config: N9K-C93360YC, layer 3 SVI created on it <<- are both 6509 and N9K run same STP mode ?
I think the trunk is STP BLK state

[gurbinder.kabbay]

I will check the STP mode as you suggested, you mean even port is up between C-->B , the only trunk can go in blocking mode because of STP ?

[gurbinder.kabbay]

Hi Experts

I have fixed this issue, it is very strange issue and it can help someone. so sharing my experience:

In current connectivity Trunk was running perfectly fine between Switch A and Switch B. (Both IOS devices).

In new Connectivity there was need to run the "switchport mode trunk" on Switch B to fix it, Although it was running fine with switch A. and in new connectivity we made the trunk between Switch C (NX-OS) and Switch B (IOS). it is very strange.. Hope it will help.

Current Connectivity: Switch A<------trunk vlan 100--------->Switch B

New Connectivity : Switch C<--------Trunk vlan100----------> Switch B

 Regards

Gurbinder