Stacked Access Switch port not showing up

[Tabish Hussain]

I have 3 access switch C9200 POE stacked and connected to 2 core switch stacked. Access and core switch are connected via LC-LC single mode fibre. However ports on both core switch 1 connected to access switch is showing up and green but the port between core switch 2 to access switch is showing up and green on core switch 2 while on access switch is showing down. Also access SW port is not blocked by STP (rapid pvst is enable). Also I can reach to internet through LAN cables connecting to RJ 45 ports of all 3 access SW. Can someone look into it and help me on this ?

Abbreviation - port= SFP port

For more info please refer to diagram. 

Thanks!

 

 

[Reza Sharifi]

Can you post "sh interface tex/x" and "sh run interface tex/x" from both sides of the connection with issues?

HTH

[Flavio Miranda]

Hi @Tabish Hussain 

 If Cores are in stack, Access are in stack and you have two connection from Access to Core and if you did not configure those interface in a port-channel, the STP will block one  port. And if not, you should be worried because you may cause a loop on the network.

[Tabish Hussain]

@Flavio Miranda 

That's the suggestion I might looking:

Can you please help me and give detailed cli command to configure port-channel because on Saturday we are going to take downtime and before that I need to figure out this thing.
Here is the scenario!

So on port 4 of one of Core Switch (in stacked), fibre is going to active access switch(in stacked) on port gig 1/1/4
On port 3 of other core switch (in stacked), fibre going to standby access switch(in stacked) port gig 2/1/3

Please refer to diagram below:

Thanks!

 

[Flavio Miranda]

Sure. You can do like this.

  For port-channel in Access switch. First you create the port-channel

interface port-channel 1

 switchport mode trunk

Then, you add the interface to the port-channel

interface Giga 2/1/3

 channel-group 1 mode active

interface Giga 1/1/4

 channel-group 1 mode active

Then, you need to do the same on the Cores.

interface port-channel 1

 switchport mode trunk

Then, you add the interface to the port-channel

interface < port3 >

 channel-group 1 mode active

interface <port 4>

that´s it for port-channel.

I advise you to also check which spanning-tree you are running and to make sure the Core is the root for the spanning-tree, as a best practice.

[Tabish Hussain]

Thank you @Flavio Miranda 

On access switch rapid pvst is running and on core switch I have to check and will update here.

Also just a side note(in the present scenario) if STP is not blocking port on access switch, then why access SW port showing down(not color is showing) and fibre connecting to it on the core switch port as up. Because if loop is forming then all the ports should be up and green and also if STP is blocking the port then atleast port should be showing amber color instead of down with no light. Any advise?

Again thank you so much!

[Flavio Miranda · Accepted solution]

On the core side is showing UP and on the Access side it is showing down? Can you share the config? Does not make sense to me.

I dont believe it is a loop either. But it can be an issue with SFP or fiber but I would expect both sides down.

[Tabish Hussain]

I don't think the problem is with SFP or fibre as I put the same sfp and fibre on active access witch and connect it to core switch 1 & both side the port is up. Only issue which I realise whenever I connect fibre from core switch 2(in stacked) to access switch(whether active or standby acc SW) port remains up on core sw 2 but fibre connecting to it on access sw(whether active or standby acc sw) is always down. So in conclusion whatever fibre I connect from core sw2(in stacked) to any one of access sw(in stacked) the port is always up on Core sw 2 but down on corresponding connected port in access switch. With core SW1 I don't have any problem as it shows up on both side.

[Flavio Miranda]

Are you able to run command now? Can you share the output of show slanning-tree?

The only explanation I can see for now would be the spanning-tree blocking one port.

[Tabish Hussain]

@Flavio Miranda 

I checked through command show spanning-tree blockedports & it showed 0 port blocked.

Unfortunately I don't have access to switch currently.

However once I get hold of it I will share all config file here.

Thankyou for taking out your time in addressing my queries.

[Flavio Miranda]

You are welcome.

When you get the change, please take the sw config and share with us.

[Tabish Hussain]

Hi @Flavio Miranda 

Turned out one of the SFP was faulty. New module will come in a week.

However, I stuck in one worrisome problem. Instead of Fibre I tried to connect core sw(stacked) and access sw(stacked) with 2 ethernet cable and all the ports was showing up even though STP is running on both SW. 

Any suggestion why STP is not blocking one redundant link? 

[Flavio Miranda]

Can I see the configuration?  And the output of show spanning-tree ?

[Tabish Hussain]

Hi, 

It is all sorted, it was SFP only that was faulty. Migration has been successfully carried out.

Thank you for the assistnace.

[Reza Sharifi]

One way to verify whether that is a loop issue or not is by unplugging the good port and seeing if the other port that is down comes up. If this is a production enviremet, you would need to do it in a maintenance window.

HTH