Spanning tree port flapping. Enhance your IT skills with our port flapping guide.

Spanning tree port flapping Solution Check the logs below to identify STP flaps in the network. Try a cable test from the dashboard to confirm and see if the port status over time color changes between dark and light green also. can someone help how to troubleshoot this issue, Apr 5, 2010 · Spanning tree issues form during the learning phase and are a result of imporper "learning" of mac address'. Switch (config)# spanning-tree portfast bpduguard default Switch (config-if)# spanning-tree bpduguard enable Ian. After the new feature is introduced, STP remains restartable during port flapping. It looks like a switch issue to me, there dont appear to be any loops - that i can see. Flapping ports can complicate your network traffic, disrupt normal network functioning, and impact the end-user experience. Jan 17, 2017 · Make sure you've got your spanning tree set up, so that a central switch is the root. A flapping port can create instability in protocols such as STP. Learn troubleshooting steps and best practices to prevent port instability effectively. Flap guard also prevents unwanted access to the physical ports. Configuring flap guard A flapping port is a port that changes status rapidly from up to down. ScopeFortiSwitch v7. Among the many features of STP, PortFast is particularly vital for improving network performance. May 8, 2024 · Use of Spanning Tree Protocol (STP): Enable and properly configure Spanning Tree Protocol to prevent loops, which are a common cause of MAC flapping. Mar 9, 2016 · As you can see I have ports flapping quite often. Oct 21, 2024 · I'm wondering if anyone else has seen this. I have reached out to Meraki support, but it was With respect to the port flapping, if this is the only uplink, users will definitely feel this, especially VoIP devices. Some of the major effects of port flapping on your network include: Topology changes. 1D Okay I have noticed I have excessive MAC flapping on all of my MS devices especially the uplinks; however, I know the first thought it to assume it is due to APs. The port states are: Dec 3, 2010 · Look for: - A link flapping on a upstream switch, causing spanning tree TCNs (topology change notifications) and spanning tree reconvergence. Here are some logs off one of them. Enhance your IT skills with our port flapping guide. If so, just replace or repair the cable and you should be good or at least have ruled that out. Dealing effectively with issues related to root ports in STP can enhance both the stability and efficiency of a network. You have to remember that the primary operating regime of VoIP devices is high-frequency, smalls payload packets. However, to harness the full benefits of STP, it must be configured correctly. Hello, we have about 20 IDFs and on all of them our Cameras are flapping on STP. e. On regular time - 1 link is in block status (Backup link) - Te4/2 Sometimes we have problem with the primary link (Te3/1) and the STP protocol change status from forwarding to blocking (flapping) how can i prevent the primary link (Te3/1) to fla Jul 29, 2024 · how to troubleshoot issues with the Spanning Tree Protocol (STP). How to Use STP to Mitigate Loops Spanning Tree Protocol (STP) and its advanced version, Rapid Spanning Tree Protocol (RSTP), help create a loop-free logical network Impact of port flapping on your network Port flapping can have serious effects on networks spanning across multiple remote locations connected by switch ports. May 14, 2016 · We have observed flapping in all others VLANs also. STP flaps can impact users heavily, resulting in dropped pings and higher latency for clients. So I went ahead and disabled STP on the switches as I am sure I don’t have any loops. Port flapping causes Understand port flapping, its causes, and impacts on networks. In older releases, when portfast is enabled on an interface and the interface is flapping, i. I can't yet make sense of it. Apr 26, 2016 · In my experience, speeds flapping has always been a cable issue. The Spanning tree protocol allows the network to include redundant links as automatic backup paths that are available when an active link fails without creating loops or requiring manual intervention. g. Check IoT and Sonos Devices: Follow our best practices to avoid loops. The normal sequence of events for a port (connected to a non-STP edge host as most IP phones are) coming on-line and then off-line is: Port is Blocked by STP Port is now on-line Port is now off-line The port enters STP blocked when it is first brought up. Requirements Cisco recommends that you have a fundamental knowledge of basic switching concepts and an understanding of Spanning Tree Protocol (STP) and its features on Cisco Catalyst Switches. STP Flapping coming from access ports? I have been looking into an STP issue that has been going on for a little while now. This article dives into common problems associated with Spanning Tree root ports Feb 12, 2014 · We currently use 12 Netgear GS108Tv2 switches and a Netgear FS728TPv2(The root switch) in a network spanning a number of islands, using radio links to connect them. show spanning-tree (shows me the state of spanning tree, which you absolutely need in this scenario) show lacp peer (this shows what the LACP system IDs are on the various LAGs) show interface poX (where X is the port channel number, shows me if the link is up and if it's flapped) show log 50 (shows the last 50 syslog messages) Jul 19, 2024 · When i let the two ports UP both of them start flapping and then they go down, but when i shutdown the second port it works, now i working with just the port channel of the N9K1, i tried to understand the issue but i don't find why would spanning three blocks my port-channel since i have vpc he should consider the two nexus as to be one switch The no spanning-tree port-priority and default spanning-tree port-priority commands restore the default of 128 for the configuration mode interface by removing the spanning-tree port-priority command from running-config. The issue isn't causing any major disruptions, but it is concerning. Mar 2, 2025 · While my network is functioning, I'm unable to view clients status, experiencing time outs or long delays accessing dashboard, and seeing spanning tree and port flapping on my MS120. Aug 21, 2025 · This article describes how loop detection and MAC flap feature work and how this can be used for monitoring and troubleshooting purposes. BR Abdul KArim Mar 22, 2022 · As far as the Spanning Tree Protocol and AP Meshing goes, I did a search for just that and found quite a few forum threads with similar problems from many different manufacturers of switches and access points. I don't think STP is the root (hah) of the issue here. Prerequisites Requirements Cisco recommends that you have a fundamental knowledge of basic switching concepts and an understanding of Spanning Tree Protocol (STP) and its features on Cisco Catalyst Switches. Sep 26, 2024 · Spanning Tree Protocol (STP) is crucial in preventing network loops, which can cause widespread disruptions in Ethernet networks. I will attempt to try the factory firmware after a few more days of testing. Feb 11, 2008 · STP uses bridge protocol data unit (BPDU) packets to exchange information with other switches. I ran it for about a month and observed this port flapping and TCP connection failure issues across all devices - I've been too busy to fix. The issue came when one of the links signal became low enough that it regularly connected and Discover expert insights on port flapping, from troubleshooting tips to unique case studies. I rebooted the switch and the ports were enabled again. The recalculation process consists of three stages: root bridge selection, port role switching, and port status transition. Poor link negotiation can cause STP priority changes (flapping), leading to persistent connectivity issues. We tried implementing RSTP on all the switches in the network and it ran fine for about a week, it managed the network as expected. ” I ran the command “show spanning-tree compatibility mode” and all of the other Aug 12, 2024 · how to identify STP flaps in the network. When the Apple TV 4K's are actively streaming, Airplaying the CRC errors disappear. - A hub or switch connected to a portfast enabled access port where this mac is learned. Today i have noticed that my DHCP server is flooded with DHCP requests by the Apple TV and started to investigate. Creating a port profile for end device ports helps since disabling STP per port is essentially the equivalent of Portfast, but without any enhancements you’d see on Jun 15, 2012 · Hii, STP domain will be affected due to port flapping. Feb 8, 2022 · Dear All, We are having 4500 Cisco Core Sw. Dec 9, 2024 · A very weird issue with Meraki MS120-48LP starting to report "MAC address flapping" on multiple wired ports. Misconfigurations can lead to performance issues, network instability, and even outages. Ensure all devices in the network support and are correctly configured for STP. The answer is to A) disable STP on one of the VLAN's (I disabled it on the VSAN VLAN as it's a completely controlled network), or B) using SSH / Terminal, set the Spanning-Tree mode to be MSTP then manually configure mst instances for each VLAN. HTH, Sukanya PS: Please rate helpful posts Due to packet changes or timer timeout, recalculation is repeatedly triggered on devices on a network. I'm also seeing spanning-tree port blocking on these ports TE3/0/1-5, but not on all of them all of the time. c) Internet Sky Q => GS108T (now swapped for an old FS105 dumb switch 100MB) => GS510TLP => Computer, WiFi, TV etc Apr 4, 2019 · We are currently experiencing something funny with the network, all devices drop for about 5 seconds - this is long enough to drop the session in ERP or VoIP calls etc. Scope FortiGate version 7. Since the faulty switch was the root bridge, it would always become root. A flapping port is a port that changes status rapidly from up to down. Both for Wired & wireless. The original STP is standardized as IEEE 802. There does not seem to be a way to keep a root port from reastablishing itself as a root port when the port has been flapping. Dec 20, 2024 · How Spanning Tree Network Super Root enhances EVPN All-Active multihoming and enables seamless loop detection and improved network stability in Layer 2. I'm seeing frequent flaps where the port goes down, stays down for a few seconds, and then comes back up. Spanning tree will converge everytime the port flaps. VLAN Configuration: Correctly configure VLANs to ensure that devices are appropriately segmented. If the access port receives BPDUs, network topology change and spanning tree network flapping might occur. Jan 23, 2004 · I know this problem of flapping sups is very rare but I needed to try and come up with a preventative measure for the future. Does this just mean the device (computer) that is attached to this port is being turned off or on? If not, then how do I troubleshoot flapping ports? I thought it might be a spanning tree issue but spanning tree has not change in a long time as shown by "show spanning-tree bridge" At this point, everything start looping, and the all ports on the Fortiwitches start flapping between the different STP states one by one, but not once the 2 port to the Cisco gets blocked. 4 (21L227) using a wired connection on a 5 port Ubiquity USW-Felx Switch. Jul 1, 2024 · Troubleshooting Common Spanning-Tree PortFast Issues As a network administrator, you’re likely aware of the critical role Spanning Tree Protocol (STP) plays in building resilient network topologies. I see a large number of STP topology changes on the network, upwards of 25ish an hour across the whole network. I have a customer that has a number of Cayalyst 9200 switches (C9200-24T, though some are 48-ports). Solution Verify Cable Connection: Ensure the cable is properly connected between the switch port and the end device. STP enables a network to have redundant paths for fault tolerance while ensuring there are no loops. Check End Device: Confirm the end device (e. Aug 11, 2019 · Note that you should see some MAC address flapping as wireless devices roam from one AP to another, but it sounds to me like your entire network is reconverging, which indicates greater issues with spanning tree. If this process repeats multiple times, STP flapping occurs and convergence fails. I’ve seen devices practically unrecoverable after a storm in a redundant star topology because the switches couldn’t keep up with STP topology changes. If a port is flapping, STP must continually recalculate the role for each port. Spanning tree provides BPDU guard feature to solve this issue. Same devices - rebooted the network to do attempt to push out new DNS settings the other day and suddenly any device with both hardwired and wifi is causing STP port blocks. Interface operating mode is STP/RSTP for vlan 1. It is interesting that the port-channel was previously working. When enabling a new port for STP the Spanning Tree Protocol goes through the following port states to get that port to be either forwarding or blocking. That is where I get confused because it is also occurring on the uplinks on MS devices that have no APs directly connected. Syntax: spanning-tree < port-list > path-cost < auto | 1. Mitigating flapping transceivers In traditional switches, the state of a link is driven directly by the reported state of the port, which is required for rapid detection of link faults. Sep 3, 2024 · This article provides steps to diagnose the Continuous port flapping on a FortiSwitch. When there are changes in the netw Feb 23, 2024 · Introduction This document describes how to troubleshoot the MAC Flaps/Loop on Cisco Catalyst Switches. I have a syslog running which appears to show “port flapping” - all the switches are older HP V1910 or A5500 Oct 20, 2008 · On Cisco switches you can use the "debug spanning-tree" and/or "debug spanning-tree events" and similar debug commands to get more information on what is happening exactly. This should be used in conjunction with step 3 below. The log files look like this: Oct 17 21:20:08 Mar 25, 2019 · The wired clients, every few seconds, give me Port STP changes/Port status changes as in designated→disabled/old: 1Gfdx, new: down / old: down, new: 1Gfdx And these are sleeping devices. Jun 4, 2011 · Flap guard A flapping port is a port that changes status rapidly from up to down. Components Used The information in this document is based on Cisco Catalyst Switches Jul 1, 2024 · Troubleshooting Common Issues with Spanning Tree Root Ports The Spanning Tree Protocol (STP) plays a critical role in ensuring a loop-free topology in network environments utilizing Ethernet. x and above. This article explores six common spanning tree problems and how to fix them, drawing on industry Jun 15, 2017 · Hello, We have 2 devices connected in stp mst mode. Valida Jun 4, 2011 · Flap guard A flapping port is a port that changes status rapidly from up to down. If your uplink is flapping, some of those packets will get eaten by the bit bucket while the link is transitioning. Spanning tree configurations on CISCO switch are as under: spanning-tree portfast edge default spanning-tree portfast edge bpdufilter default spanning-tree extend system-id spanning-tree mst 0 priority 24576 At MOXA switches we have configured RSTP. Looks like the port is flapping. Aug 28, 2024 · This document describes how to use Cisco IOS® software to troubleshoot issues with Spanning Tree Protocol (STP). However, the consequence of this is that a marginal transceiver, optical, or wire cabling, one that "flaps" up and down several times per second, can cause STP and other protocols to react poorly, resulting in Mar 23, 2020 · Troubleshooting STP instability Spanning Tree Protocol A Layer 2 network protocol that ensures a loop-free topology for any bridged Ethernet LAN. Jul 2, 2024 · The new feature maintains STP restartability while a portfast-enabled port’s link status changes. Which also give a high proportion of CRC align errors, only on received. It seems some of the Uplinks are flapping and i dont exaclty know where its happening. Managed FortiSwitches of version 7. There are no network loops, this is a very simple topology. Spanning Tree Protocol (STP) is a link-management protocol to enable a layer 2 loop-free topology. Jun 12, 2019 · The new feature maintains STP restartability while a portfast-enabled port’s link status changes. Oct 9, 2014 · BPDU Guard is disabled on all switch ports by default - you'd need to enable it either per-port or globally. If you have a spanning tree issue, or think you might, then check this link out: Mar 8, 2019 · In the logs I can see for every port on the switch:- Port STP change Port x designated→disabled Port status change port: x, old: 1Gfdx, new: down Why would STP disable all the ports on the switch at the same time? No other switches are affected, just this one. , PC, AP) is connec Apr 18, 2024 · Apple TV 4K (2nd generation) - flapping network port during standby Hi I have a Apple TV 4K (2nd generation) A2169 running tvOS 17. There is a 3 second delay before the port can be brought on-line. A flapping port can create instability in protocols such as Spanning Tree Protocol (STP). There is also a high rate of STP topology changes occurring. If you don't configure spanning tree priority, a random switch becomes root (the one with the lowest MAC address) - if that's a phone switch or any other 'peripheral' switch you're bound to have unexpected reconvergences. They are both getting flooded with logs saying “%STP_COMPATIBILITY_MODE: STP:Compatibility mode change received for interface port-channel1. The common causes are as follows: Link fault: The link attributes such as the port Mar 3, 2025 · While my network is functioning, I'm unable to view clients status, experiencing time outs or long delays accessing dashboard, and seeing spanning tree and port flapping on my MS120. What I think is happening is that as the interfaces leave the port-channel on the Arista, it is generating BPDUs with different source MAC addresses. , going up and down, STP becomes non-restartable. Jan 10, 2024 · On my 3850 I'm seeing MAC Address flapping between any of the TE3/0/1-5 ports and the TE3/0/12 port with the mac address of my router. Hey everyone, we have a pair of Dell S-5212FON switches that keep flapping between STP and RSTP on a port-channel. Where would you recommend to… I have a long, long history of dealing with Ubiquiti and STP issues. . Check your cabling or the nic on the server. You will see those spanning tree logs any time a port comes up. - A unidirectional link on an upstream switch causing the loop. 200000000 > Assigns an individual port cost that the switch uses to determine which ports are forwarding ports in a given spanning tree.