Link up & down Repeatedly

fbabashahi · ‎06-30-2021

Hi , I have a switch 3750 stacked , I don't have IP-phone some of my links get up & down repeatedly (I see this in switches 2960 too)

Jul 1 10:24:12.159: %LINK-3-UPDOWN: Interface GigabitEthernet2/0/3, changed state to down
Jul 1 10:25:03.831: %LINK-3-UPDOWN: Interface GigabitEthernet2/0/3, changed state to up
Jul 1 10:25:04.838: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/3, changed state to up
Jul 1 10:25:07.815: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/3, changed state to down
Jul 1 10:25:08.814: %LINK-3-UPDOWN: Interface GigabitEthernet2/0/3, changed state to down

The port config as below , I read that it might be for power inline so I disable it .

interface GigabitEthernet2/0/3
switchport mode access
power inline never
spanning-tree PORTFAST edge
spanning-tree BPDUGUARD enable

What should I do?

How to prevent the port from this behavior?

Leo Laohoo · ‎06-30-2021

Post the complete output to the command "sh interface G2/0/3 controller".

Then do the following:

1. Command: test cable tdr interface G2/0/3

2. Wait for approximately 5 to 7 seconds for the test to run it's course

3. Command: sh cable tdr interface G2/0/3

4. Post the complete output to #3

fbabashahi · ‎07-01-2021

Hi @Leo Laohoo this is the output

SW-CORE# sh cable tdr interface G2/0/3
TDR test last run on: July 01 11:31:14

Interface Speed Local pair Pair length Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi2/0/3 auto Pair A 17 +/- 10 meters N/A Open
Pair B N/A N/A Normal
Pair C N/A N/A Normal
Pair D 17 +/- 10 meters N/A Short/Crosstalk

Leo Laohoo · ‎07-01-2021

@fbabashahi wrote:

Pair A 17 +/- 10 meters N/A Open
Pair B N/A              N/A Normal
Pair C N/A              N/A Normal
Pair D 17 +/- 10 meters N/A Short/Crosstalk

Faulty cable nearest the phone.

fbabashahi · ‎07-01-2021

@Leo Laohoo

I don't understand i don't have phone in my network!!!

Also i did not change cabling.

what does it mean? and what should i do?

balaji.bandi · ‎07-01-2021

Get new Patch cable ( cat 5/ Cat 6 - RJ 45) and connect to end device and test it.

BB

***** Rate All Helpful Responses *****

How to Ask The Cisco Community for Help

Leo Laohoo · ‎07-01-2021

The remote-end has a faulty cable.

MHM Cisco World · ‎07-02-2021

BPDUguard make the interface err-disable and if you config the interface to be automatically UP again then you will face up down,
just check when the interface is down
show interface status,
check if interface is err-disable,
I think the issue here is BPDUguard with interface connect to other L2 SW.

mayank srivastava · ‎07-02-2025

This is happening on our switch CBS350 ports that are connected to the Polycom (VOIP phones). This usually occurs at midnight, which causes call delays. I searched a lot on the internet but was unable to find any precise answer.

2147481750	2025-Jun-29 00:09:56	Informational	%LINK-I-Up: gi17
2147481751	2025-Jun-29 00:09:56	Warning	%STP-W-PORTSTATUS: gi17: STP status Forwarding
2147481752	2025-Jun-29 00:09:53	Warning	%LINK-W-Down: gi17
2147481753	2025-Jun-29 00:09:51	Informational	%LINK-I-Up: gi17
2147481754	2025-Jun-29 00:09:51	Warning	%STP-W-PORTSTATUS: gi17: STP status Forwarding
2147481755	2025-Jun-29 00:09:48	Warning	%LINK-W-Down: gi17
2147481756	2025-Jun-29 00:09:42	Informational	%LINK-I-Up: gi17
2147481757	2025-Jun-29 00:09:42	Warning	%STP-W-PORTSTATUS: gi17: STP status Forwarding
2147481758	2025-Jun-29 00:09:39	Warning	%LINK-W-Down: gi17
2147481759	2025-Jun-29 00:09:35	Informational	%LINK-I-Up: gi17
2147481760	2025-Jun-29 00:09:35	Warning	%STP-W-PORTSTATUS: gi17: STP status Forwarding
2147481761	2025-Jun-29 00:09:25	Warning	%LINK-W-Down: gi17
2147481762	2025-Jun-28 10:45:04	Informational	%PNPAGENT-I-BYEREQ: Bye PnP Request
2147481763	2025-Jun-28 10:45:04	Informational	%PNPAGENT-I-RESPSUCCESS: PnP Response Success
2147481764	2025-Jun-28 10:45:04	Informational	%PNPAGENT-I-BACKOFFCALLBACKAFTER: Backoff PnP Request with <callbackAfter> has received: 24 Hours 0 Minutes 0 Seconds
2147481765	2025-Jun-28 00:05:02	Informational	%LINK-I-Up: gi17
2147481766	2025-Jun-28 00:05:02	Warning	%STP-W-PORTSTATUS: gi17: STP status Forwarding
2147481767	2025-Jun-28 00:04:59	Warning	%LINK-W-Down: gi17
2147481768	2025-Jun-28 00:04:57	Informational	%LINK-I-Up: gi17
2147481769	2025-Jun-28 00:04:57	Warning	%STP-W-PORTSTATUS: gi17: STP status Forwarding
2147481770	2025-Jun-28 00:04:54	Warning	%LINK-W-Down: gi17
2147481771	2025-Jun-28 00:04:47	Informational	%LINK-I-Up: gi17
2147481772	2025-Jun-28 00:04:47	Warning	%STP-W-PORTSTATUS: gi17: STP status Forwarding
2147481773	2025-Jun-28 00:04:45	Warning	%LINK-W-Down: gi17
2147481774	2025-Jun-28 00:04:41	Informational	%LINK-I-Up: gi17
2147481775	2025-Jun-28 00:04:41	Warning	%STP-W-PORTSTATUS: gi17: STP status Forwarding

balaji.bandi · ‎07-02-2025

configure port in portfast so this will not get in to election STP process.

BB

***** Rate All Helpful Responses *****

How to Ask The Cisco Community for Help

mayank srivastava · ‎07-03-2025

PortFast is enabled on all ports by default

balaji.bandi · ‎07-03-2025

Can you post

show spanning-tree interface G17 detail

if you dont use pnp - try disable

no pnp enable

BB

***** Rate All Helpful Responses *****

How to Ask The Cisco Community for Help

mayank srivastava · ‎07-07-2025

OH009SW1#show spanning-tree gi17

Port gi17 enabled
State: forwarding Role: designated
Port id: 128.17 Port cost: 20000
Type: P2P (configured:Auto ) RSTP Port Fast: Yes (configured:Yes)
Designated bridge Priority : 32768 Address: cc:b6:c8:cc:97:85
Designated port id: 128.17 Designated path cost: 20000
Guard root: Disabled BPDU guard: Enabled
Number of transitions to forwarding state: 0
BPDU: sent 4799541, received 0