PC ports connects to Vlan access and have a port loop on Cisco C9200

[Xx20GaryL21xX]

Hi All,

C9200  Etherchannel --> C9200 at the same site

We have layer 2 Vlan setting (Vlan 100 - 106) + RPVST spanning tree. 

Switchport

SW1: Vlan 100 - 106 Root Primary 

SW2: Vlan 100 - 106 root secondary

Etherchannel Trunk mode (allow 100, 101) Active Active

Trunk port (allow 100, 101) to other site 

The main issue:

We found out by Wireshark on PC that there are a loop itself on same source MAC to Dst MAC message. It is the same port connected to PC. 

Gi1/0/18 I tried to use as below:

1. portfast, bpduguard enable,

2. switchport port-security, maximum 1, violation shutdown.

it still show up a loop with same port/mac by wireshark.

Other than that, there is not log shows up that have loop issue on port on cisco switch. 

We do not have an clue how to fix this issue.

Do anyone able to help me for that?

Thanks,

Gary

[Georg Pauwen]

Hello,

odd indeed. A loop on a single port ?

Can you post the running configs of both switches ? Maybe we can spot something. Does the loop occur with the same PC on other ports as well ? If it is one particular PC, it could be a malfunctioning NIC...

[Xx20GaryL21xX]

Hi  Georg,

Yes, A loop just only a single port.

I posted the show run as attachment. I tried to plug in on other single ports with different vlan access port and PC. It also got same result for single Port Loop by Wireshark.

It checked on that PC port by Wireshark as before it also have ARP issue that cannot reach the Gateway and come out a lot of broadcasts. We have figure the issue which come from their Virtual IP on other site. 

Please have a look on my running config first.

odd indeed. A loop on a single port ?

"Can you post the running configs of both switches ? Maybe we can spot something. Does the loop occur with the same PC on other ports as well ? If it is one particular PC, it could be a malfunctioning NIC..."

Thanks,

Gary 

[Georg Pauwen]

Hello,

the first thing I noticed is that you have 'ip routing' enabled on both switches, but no apparent IP addresses and routes ? Is that on purpose ?

[Xx20GaryL21xX]

Hi,

This IP routing setting used for InterVlan routing before, but it is not enough ip to use and we have our Esxi server with their owned IP routing, so we just left that to Layer 2 Vlan setting without IP on our switch. 

We can delete for that, if it is not purpose to do now. 

It is not effect for this loop issue, right? 

"the first thing I noticed is that you have 'ip routing' enabled on both switches, but no apparent IP addresses and routes ? Is that on purpose ?"

[paul driver]

Hello

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@Xx20GaryL21xX wrote:

The main issue:

We found out by Wireshark on PC that there are a loop itself on same source MAC to Dst MAC message. I

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Not sure what your looking at, Could you post what your are seeing please.

[Xx20GaryL21xX]

Hi Paul,

I attached our wireshark from our remote PC that plug in the issue port for a loop.

1. In our etherchannel setting, do this effect for this loop issue?

2. We just focus on our PVST STP setting before, we believe that it would be the STP cause this loop issue. However it have an loop the single port itself, when plug in PC port for remote and wireshark checking purpose.

We tried to use portpast, bduguard, portsecurity, violation shutdown and it has the same result.

It did not have any log show up on cisco switch and only found out on wireshark.

I have not any clue or ideal how to fix it. Do you have any suggestions?

Best Regards,

Gary