Questions tagged [spanning-tree]

For questions about Spanning Tree Protocol (STP), a common protocol to prevent bridge loops at OSI layer-2.

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Why switch uses Mac address during implementation of spanning tree protocol (STP)?

We know that layer2 switch doesn't use Mac address ,uses only certain port number to accept the frame. But I have been read on book as well as internet that uses Mac address to find spanning tree for ...
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Which interface will be the root port in this topology?

I am currently studying for my CCNA and the current topic is STP. I ran into this topology and it caused me some confusion. I was trying to identify the root port for SW2. Here was my logic for that. ...
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HP 6120XG switch LACP is blocked - error condition

Folks, I am dealing with very strange issue related LACP and not sure if its bug of 6120XG switch or something else. so let me explain my issue here. Network Diagram: I have two Cisco Nexus 9396PX ...
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what is switch device mac address?

I'm studying STP protocol and how to configure STP on switches. I know each switch has several ports and each port has one MAC address. but when I read the below article I noticed that it allocate one ...
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What is the behavior of two managed switches connected to one unmanaged switch?

Image the followign scenario Switch 1 Managed (root) Switch 2 Managed Switch 3 Unmanaged They are connected as follows: Switch 1 <-> Switch 3 Switch 2 <-> Switch 3 Switch 1 <-> ...
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RSTP / MSTP use cases and best practices

Hi, what would be the best practice to achieve separate tree topologies for each of the rings? Two options come to my mind, although I do not completely understand IF RSTP can be made VLAN-aware ...
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Using PT and EtherChannels along with STP

I'm very new to all of this but I am trying to create a network topology as practice that uses three etherchannels across three switches and then rely on STP to block one. So far it was working well. ...
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Error cluster with packets balacing through NAT

Im trying to make a web cluster (HTTP and FTP) with 3 linux machines where the packets are balanced through NAT and im using Bridge interfaces and HSRP, because im using 2 routers(using c3660 image) ...
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STP convergence process needs detailed explanation, please

So, I understand how STP convergence works on high-level. However, when I am trying to look into the process deeper, I run across some doubts I would appreciate someone could clarify to me. Here we go:...
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4 votes
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MSTP with different VLANs blocking port

I am trying to use MSTP with HP Procurve switches. The edge switch (D in diagram) has half of the ports set to VLAN10 and half set to VLAN20, all untagged. The problem is that the switch D to forward ...
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STP frames over VPLS/VPWS

Do VPLS and VPWS services transfer STP frames? How about other L2 control frames? Can two geographically dispersed sites have one STP region over any L2VPN?
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what is the main function of root bridge and ring master?

When we learn the STP or RSTP,we all learn the election of root bridge, the lowest priority number or MAC address of switch will become the root bridge.So here is my first question: 1.So what can the ...
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Why does only the root bridge send RSTP BPDUs after sync?

From a recent packet capture, after the sync process in RSTP, only the root bridge sends RSTP BPDUs every 'hello' interval. Why is it so? Shouldn't all switches send BPDUs every 'hello' interval since ...
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3 votes
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Why does RSTP send proposal bit and agreement bit as '1' initially?

From a recent Wireshark capture of a RSTP BPDU on a switch, both proposal and agreement bits were set to '1'. In my understanding, initially both switches 'propose' themselves as root. The better root ...
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The difference between data frame and BPDU in STP

There are two of port states in STP: Disabled and Blocking,and the a website explain their difference Disabled : This port is shutdown,and it won't send or receive any frame Blocking : This port won't ...
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6 answers
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Why does STP choose the lowest bridge ID as the root bridge?

The switch which has the lowest bridge ID can be the root bridge,and the bridge ID is made of priority and MAC address,that is , bridge ID = priority + MAC address So we will choose the switch which ...
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2 votes
1 answer
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STP Loop issue on long distance link

I have long distance connectivity between west coast to east cost datacenter via our ISP network as you can see that in following diagram (BSN=Boston, PHX=Phoenix) Now when ISP-A or ISP-B doing any ...
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Ramifications of turning off Spanning Tree for EIGRP network?

Ran into something I've never seen before in a production network I'm new to supporting and wanted to get the communities take on it. I have an EIGRP network that interconnects about 60 sites across a ...
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How can a topology have a switch with 3 segments that are unblocked? (Spanning Tree Protocol)

I am quite confused after doing some research online regarding designated port selection. It looked like to me that each port segment has a designated port and a blocked port? If you look at the ...
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RSTP: Max Aging and Device Count

I have a question about the RSTP ethernet swtiches, I have 40 RSTP ethernet switches, they connect with the line topology and root birdge is 23th device on the line. I am using just 23 device for this ...
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RSTP Network Switches Port Base MAC Address

How to ethernet managable network switch manage the dynamic table entries although receive "port base MAC address frame" like RSTP,STP protocole ? I know the dynamic mac table save the ...
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BPDU Guard With RSTP Devices

I am attempting to secure our switches with BPDU Guard. I have it enabled and I have a pieces of equipment with 2 NIC ports on them of which they can be daisy chained together for data collection. ...
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Losing connection when connecting a server to Stratix 5400?

I have a problem that when connecting a server to Stratix 5400 the Stratix loses connection for some seconds which causes a Safety Fault for the line because we have Safety PLC’s any help. ,Software ...
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What are the differences between root primary and secondary?

Hello I am new at networking and studying for CCNA. There is a paragraph like this in the book and I am struggling about understanding well. Maybe it's because english is not my native language. ...
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How does STP attack work?

I was reading how STP works and an idea came to my mind. I thought about an attacker can add a new switch (somehow, i don't know if it can be done remotely) or can manipulate the existing switch's ...
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Layer 2 path selection

So i know this in stp domain if you want to influence traffic you. Eed to increase the port cost on the undesirable port for the desired vlan or mst instance and it worked for me,but on a non root ...
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Why would a unidirectional link failure cause a switching loop?

Based on what I've read so far about UDLD and LoopGuard, it seems that in the case of a unidirectional link failure, a switching loop would form because the blocking port would transition into a ...
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How does a switch decide what mac to use for Root election in STP?

I know that for the STP a root switch or bridge is to be elected based on the BID that consists of a priority value and the MAC address of a switch if the priority is the same then the MAC is the ...
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Network topology with big spanning tree diameter

I have a quite big network with spanning tree diameter 26 (if I count it correctly). It is build on Cisco swithes (mainly Catalyst 2960 and Catalyst 1000, two SG350), running rapid-pvst. It is now ...
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Mac Instability in STP after topology change!

So I'm learning about STP and I recently been taught that when the topology is changed due to direct or indirect Link failure a Mac Instability could occur, So I was wondering, If the blocked port is ...
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Non [R]STP switches in LAN ring topology

I am revamping a simple network, which is based on cascaded, standard, unmanaged PoE switches. I am also adding a redundant loop closing wire, from the last switch to the first one, which at the ...
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2 votes
1 answer
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In RSTP, where all switches generate their own BPDUs, are they limited to forwarding them only on designated ports? (like in classic STP)

I recently learnt a rule in STP: only Designated ports forward BPDUs. However, I'm not sure about this in RSTP since ALL switches generate their own BPDUs every few seconds. So, in a certain LAN ...
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RSTP sending BPDUs out of the network switch?

I need some information about RSTP If the port state is blocking, discarding alternate . Should BPDU be sent to external ports? I cant see any BPDU in wireshark if the port states Alternate,Discarding ...
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STP configurations

In my design, there will be a few be a few rings of edge switches that are connected to my distribution switch. (alcatel 6860-U28) The distribution switch will then be connected to my core router ( ...
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Aggregation links and RSTP

If aggregation links are used for redundancy to ensure the devices stay active if a link fails, does RSTP need to be configured due to there being 2 links?
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How loops appeared when skipped listening and learning state?

In STP convergence process, I just know that after a link failed a blocking port become listening state for 15 seconds then learning state for 15 seconds. I've read a CCNA 200-301 Guide explained me ...
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Can we use both RSTP and MSTP spanning tree protocols in same network

I have network connecting with 500 users and 50 servers connecting different layer3 switches and layer2 switch. Can i run rstp in few switches and mstp on remaining switches.
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Recommended switches and routers configurations for a building of 5 floors?

Just recently I had an interview for a network Engineer position. The interviewer asked me the following: You have a building of 5 floors, where each floor has around 30 employees. What is your way of ...
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Why some situations, PC can connected to trunk port and work fine?

I want to know about tagged and untagged vlan mechanism then I try to configure like this When I connected PC3 to trunk port on Packet Tracer, It doesn't work and a switch dropped PC3's frame if I ...
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Can link aggregation be substitute for stp protocol?

Can link aggregation be a substitute for STP protocol? I mean can I use 2 links with Link Aggregation to connect two switches for higher availability as an alternative to STP protocol?
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Using MSTP with RSTP

I have two layer-3 switches connected with two redundant links that I'm trying to run PTP OSPF sessions across, a la: (OSPF) VLAN 1002 - - - - - - - - - - - - / ...
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How would a bridge loop occur?

As I understand it, STP is used to prevent bridge (/switch) loops, which will typically occur in the case of redundant links on a switch. But how can a loop occur and cause a broadcast storm? If a ...
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RSTP - minimum hello time?

1) What's the minimum possible "hello time" for Rapid Spanning Tree (RSTP)? Is it possible to reduce the hello time to e.g. 0.1 seconds? 2) Is the minimum dictated by the RSTP standard, or would it ...
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Do I need STP enabled on all switches in a loop?

I have a network architecture where each of my N switches is connected to two others, making it a perfect loop. For example see the diagram below: I know that in order to avoid broadcast storms, I ...
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RSTP Sync received every 2 minutes after a TC

While digging into logs (debug spanning-tree event has been enabled) in order to troubleshoot communication losses after topology changes. I was able to notice once I triggered a TC, one specific ...
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Why doesn't STP apply only to broadcast/unknown unicast frames?

All known unicast/multicast frames shouldn't cause loops since they have a known destination. So they can use all the available bandwidth. What am I missing?
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What is the impact of VTP pruning against RSTP topology?

While working on a network using VTP (without pruning yet), I noticed the STP topology (for VLAN 10 let say as an example) was including all switches even the ones not having any interface in the VLAN ...
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End to End propagation delay computation for STP

While reading a bunch of details about STP timers on this Cisco website https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/19120-122.html#f1 I could not understand how ...
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Why does HPE disable STP by default? [closed]

It this certainly true that switches needs STP to avoid loops or broadcasts storms, but recently I saw the configuration of my Hewlett Packard switch and I noticed that it has STP feature disabled by ...
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2 votes
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Is there a problem with "max age" definition in STP?

In "CCNP and CCIE Enterprise Core ENCOR 350-401 Official Cert Guide" we have this definition of max age: Max age: This is the maximum length of time that passes before a bridge port saves its BPDU ...
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