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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In STP, how does a switch know that a peer port is blocked?
Let's consider the below image:
Let's assume the following:
Cat1 is the root bridge
fa0/23 on cat2 is blocked after stp has converged
When a frame arrives at cat1 to be forwarded to cat2, how ...
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Spanning Tree Protocol - Redundant Links
There are two things about STP that confuse me.
Consider the following network:
There is a designated port from S1 to S3. There is also one from S1 to S2, and then S2 to S3.
If S1 sends an unknown ...
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RSTP convergence of p2p links
Ramping up on RSTP here. One thing that is unclear to me is how RSTP links converge initially on P2P links. Consider the classic 3 switch topo as below:
For RSTP, won't all the links move to ...
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2
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Juniper EX bpdu-timeout-action not blocking interface
In short
I'm trying to configure bpdu-timeout-action block on trunk interfaces to other switches, but it doesn't go into blocking mode when there are no BPDU's received (eg, when connecting my laptop ...
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What Does Exactly Happen When A Switch Is Connected To A Portfast Port?
I am trying to get a thorough understanding of what does happen when a switch is connected to a portfast port on another switch that is part of a stable STP network in case of:
1- the port has no ...
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How does STP technically generate the path cost for an interface?
How path cost is being calculated in STP is still not clear to me.
Let's say we got this architecture, where all switches were just turned on for the first time:
During BPDUs exchange, every switch ...
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how can a STP switch time out MAC addresses from the table in Listening state?
I am looking over some materials describing STP's port states (the original version from 802.1d) and they say that a port in Listening state can not modify the MAC address table (it doesn't learn new ...
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Two switches, double connection, no LACP: how does it work?
We have a network with an HP 1910-24 and a V1410-16 (unmanaged). The two are connected via two network cables, but there's no Link Aggregation configured on the 1910, and all the connections are ...
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Spanning-Tree vlan priority on a pass through switch
I am still understanding a bit about this priority for spanning-tree on VLANs. I have a SWITCH A that is the root of a VLAN. It trunks through SWITCH B with no ports on that vlan. SWITCH B trunks to ...
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Loops in an STP-enabled network - How?
I've got a question about STP/RSTP (it applies to both, but I'll just say STP). If I connect several switches and the STP algorithm eventually creates a loop-free environment, then how can a single ...
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MST - multiple instance design in single region
I am preparing for migration of this rather simple network layout from RST to MST:
From what I have read so far, it looks like the best approach is to avoid interoperability issues and simply rollout ...
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Is non-blocking per-VLAN (rapid) spanning tree configuration possible?
Imagine a pair of switches connected with a couple of trunk links created in the following fashion:
Assuming the numbers on lines correspond to different VLANs, how would you arrange a working ...
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Do STP 802.1D support Uplink Fast, Backbone Fast and Port Fast?
Do STP 802.1D support Uplink Fast, Backbone Fast and Port Fast ?
Aren't these features cisco proprietary ?
Is IEEE later add these feature into 802.1D ?
If so, Why are they not called Alternate Port, ...
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HSRP does not work on two switches. Cisco
The problem is this: clients receive IP addresses from the L31 DHCP server, but they cannot ping the gateway, although HSRP seems to be working, there are no problems, I suspect that this is a bug in ...
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Cisco device chooses link with higher cost as the root
The problem is that psw11 (SG350-28P) is choosing the path to sw10 (C2960L-48TS-LL) with a cost of 20000 as the root instead of the path to sw56 (C2960L-48TS-LL) with a cost of 10000, even though the ...
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Palo Alto 440 and FS 5860 Switches -- L2 Loop/Spanning-Tree issue
I have identified what seems to be a looping issue, due to STP not blocking an alternate path. As you can see in the diagram, ports Eth7 and Eth8 on the switches connect to the Active/Passive PA-440 ...
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Alternative Solution to Avoid Loop aside STP
SITUATION: I have two switches SW1 and SW2. These two switches are connected with two trunk ports. While SW1 is connected to PC1, SW2 is connected to PC2.
If PC1 sends a broadcast frame to PC2 via ...
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How would a switch know that it should forward a frame through a different interface in a STP topology?
Imagine the following STP topology
If PC0 was to ping PC1, all of the switches would create entries in their MAC table according to the source MAC address of the PCs associated with the corresponding ...
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Is it risky to change hardcoded STP mLAG port cost on Cisco Nexus LACP port
When two Cisco Nexus are connected in VPC, the stp cost is hardcoded to 200 for the mLAG LACP ports.
I would like to manually change the cost on my devices because my 2G and 200G links have the same ...
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Spanning tree loop prevention
Can I get some advice on what STP features to enable as best practice please, mainly to mitigate loops? In the past a user mistakenly connected two floor ports together causing a loop.
Below are the ...
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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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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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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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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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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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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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