Questions tagged [spanning-tree]
For questions about Spanning Tree Protocol (STP), a common protocol to prevent bridge loops at OSI layer-2.
327
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Cisco IOS Switch: Why is "no spaning-tree vlan XXX" automatically inserted on vlan creation?
Yesterday we added a few VLANs (218-220) to one of our core-switches (WS-C3560X-24, c3560e-universalk9-mz.122-55.SE3 running as vtp-server) and noticed that a configuration directive no spanning-tree ...
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2
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Finding the optimum root bridge for a spanning tree
The spanning tree protocol uses the bridge ID and the MAC address of the switch to elect the root bridge. After the election process, a spanning tree is created, preventing switching loops by ...
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4
answers
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H3C MST BPDU exchange failing
I am coming across the following MST issue.
Between a HP5940 network core and HP5130 network access layer, I am using 5 instances of MST, configured like this :
CORE switch
stp region-configuration
...
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1
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0
answers
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How does Fabric Connect protocol work?
What are the algorithms that are used by Fabric Connect protocol/protocols to choose the best path to forward a packet?
I know that Fabric Connect is used to replace the Spanning Tree Protocol that ...
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2
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1
answer
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Two physical links, different VLANs, no PO. Will PVST shut one link down?
Two devices - switch A and switch B - two physical links (not bonded/channeled) between them. First link is configured for say - access VLAN 10, second for access VLAN 20 (but really it could be two ...
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2
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Why in STP is the switch that is the "center" of the network is called the "Root Bridge," not "Root Switch"?
I am interested in the terminology of the term "root bridge." Why was this word chosen instead of the word switch, which would have been more intuitive?
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1
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BPDUGuard and BPDUFilter on Spanning Tree Edge Port
What is the difference between 2 ports configuration
interface Ethernet1/10
switchport
switchport access vlan 10
spanning-tree port type edge
spanning-tree bpduguard enable
spanning-tree ...
user38976
0
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1
answer
579
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STP interface command shutdown STP globally
I'm in the process of studying to renew my CCNP again. 3 years comes and goes awful fast! While working on my lab gear I thought I wonder if I can shut down STP on a single interface like I've done in ...
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1
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CIST starved for a bpdu Rx on port 17, temporary fix
I would like to know if modifying the Hello timer on specific port could fix at least temporary our problem ?
We have a L2 link between 2 distant places and it seems the provider is dropping some ...
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2
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2
answers
603
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Cisco CLI STP VLAN removal
Consider the following in the running config in Cisco IOS (switch):
spanning-tree vlan 2-20 prio 4096
If the command "no spanning-tree vlan 5 prio 4096" is issued, will only VLAN 5 be removed ...
- 837
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1
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Understanding how spanning-tree protocol (STP) works, along with CDP and DTP
I have made the following simple network model on packet-tracer consisting of two laptops and a switch. I don't do any configurations on laptops or switches, the only thing I do is connecting them ...
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2
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Does SPB really replace STP?
I have been reading IEEE 802.1Q 2014 about SPB. I also have watched a few videos about SPB on youtube. However I don't understand why no one mentioned that BPDUs are still transmitted in the network, ...
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2
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Manager states we cannot put retail switches on network due to fear of non-STP config and network storm problems. Is this true?
I'm a desktop support engineer working with a Cisco certified manager. I value her opinion greatly when it comes to networking issues. However, I'm split on this because with my knowledge of ...
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2
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L2 network design questions
Good afternoon everyone.
I would like to know the textbook answer to a network I've been asked to assist with.
I have an IT cupboard which serves the location as the MDF. I then have a variety of ...
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2
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How do modern switches forward ethernet frames logically?
I'm having my googlefu fail me. I have a rather complicated network that has grown organically that now is running a mix of IBM / BladeOS switches that are doing VLANs and MST for spanning tree, ...
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spanning tree, how can I change the path?
I have 2 Switches I made either channel between them , but every switch is connected with other links through other switches that can reach the destination and the spanning tree makes the channel not ...
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1
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Cisco STP issue with BIG IP F5 trunk
We have above network and here is the cisco trunk configuration.
Nexus 5548
interface Ethernet1/9
description F5-10G-Link
switchport mode trunk
switchport trunk allowed vlan 201
Cisco 3850 (...
- 4,351
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1
answer
429
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How can I prevent VLAN bridging on a Cisco switch
A Cisco switch (IOS) on our network configured with VLAN 7 and VLAN 8 as access VLANs (7 being the native for the trunk on the switch) had the VLANs bridged by someone who connected a patch cable from ...
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0
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163
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When exactly the Proposal and Agreement flags are used in RSTP
When does the flags proposal and agreement are set in RSTP? What are its importance?
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2
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597
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VSS back to back like vPC back to back
I know vPC back to back to avoid spanning tree between two pairs of Nexus.
But I've two 4500 pairs and I need to connect them. Is there a way to do something similar to the vPC back to back to don't ...
- 180
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2
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Spanning Tree cost calculation
We have following network diagram, but SW3 isn't in place, and I have a question before I plug SW3 into the network.
Sorry, I put in the wrong diagram before. The following diagram is the correct one:
...
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1
answer
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Why is there a large difference between BPDUs sent and received counters for RSTP root port?
I just noticed a big difference in numbers looking at the sent and receive counters for RSTP BPDUs.The port I'm looking at is a root port. I see a very less number of BPDUs sent against to BPDUs ...
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4
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2
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RSTP Troubleshooting
We have about 30 switches (multiple vendors) in a network which consists of a main ring and several branches. A couple of the branches may have loops. Some of the switches are smart switches with ...
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1
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Even after the spanning tree is determined why Root Bridge periodically send configuration message.
Even after the spanning tree is determined why Root Bridge periodically send configuration message.
2
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1
answer
356
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Should we trunk between L2 AS switches? Or send everything to the L3 DS?
Given the diagram below, does it make sense to trunk between the L2 access switches? Otherwise, all VLAN 10 and VLAN 20 broadcast domain traffic has to go through the L3 distribution switch.
Thick ...
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4
answers
569
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Building too large for ethernet runs
I'm pretty new to network design. I know enough to wire small buildings and such, but I'm puzzled as to how work this one out.
A building I'm working on is an odd shape, and very large. ...
user34833
1
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2
answers
269
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STP / Why one end is in BLK state?
So I've had a question that I haven't had a real answer to, I'm not even sure if there is an answer other than "That's just how the algorithm does it."
So why does STP only block one end of a line on ...
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3
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5
answers
2k
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Path cost between a different bandwidth interface in STP
I've got a terrible doubt that does not let me sleep for last few days. I have a network with different bandwidth interfaces (Gi0/2 and F0/2). The interfaces to which I'm referring are the ones inside ...
1
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2
answers
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MST region and CST virtual bridge priority
In Multiple Spanning Tree, 802.1s, an MST region appears to the external world (another MST region, a 802.1d or 802.1w switch) as a single (virtual) bridge, using its IST instance.
What is the ...
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spanning tree at layer 3
we want to prevent loops in the network be it LAN or WAN. However for layer 2 LAN networks STP is used to prevent looping switches.
However at layer 3 TTL field is used.
why not use STP for layer 3 ...
- 1,237
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3
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Possibilities to switch between primary and backup radios between locations
What are the possibilities of connection/link failover in the following configuration:
2 geographic locations connected by 2 independent radios (a primary and a backup, the backup is a mikrotik device)...
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4
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0
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Regarding vPC Dual Active or Split Brain scenario
Consider the below topology:
Imagine that both the vPC peer keepalive link and vPC peer link have gone down.
I am trying to understand how will that lead to unpredictable traffic flows or loops.
...
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6
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2
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Should I disable STP on my access ports?
I'm going to replace some old "central" access switches to some Cisco Catalyst 2960X, and I'm not sure what to do on their STP configurations.
For this network, we have some "central" access switches,...
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3
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STP port flapping
First of all devices:
HP ProCurve Switch 2610-24-PWR
Cisco IP Phone 8811
PC
I'm receiving loads of logs like these:
I 01/16/17 23:58:39 ports: port 20 is Blocked by STP
I 01/16/17 23:58:39 ports: ...
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Root path cost?
A little confused here. Im trying to determine the root port for SWITCH B. SWITCH C here is the ROOT SWITCH. I understand that to determine the root port you need to find the lowest cost path to the ...
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1
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STP Protocol issue
I am facing STP issue in my network.
I configured STP protocol in two branches like Building A and Building B both are Cisco SG300 24 port switch.
I configured dual Link primary and secondary which ...
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1
answer
115
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STP - Port path cost won't update
Those are the default path cost for STP :
10 Mbps --> 100
100 Mbps --> 19
1 Gbps --> 4
I have this topology :
All interfaces are set to 100Mb/s so each path cost is equal to 19. I forced the ...
- 115
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1
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Understanding virtual port channel peer switch command
1.I understand that irrespective of the STP priority, vPC primary always sends the BPDUs.The vPC secondary device will just proxy those BPDUs.
Please confirm if the above understanding is correct.
2....
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1
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Regarding Bridge Assurance feature
In one of the articles i read the following regarding Bridge assurance:
"When enabled, BDPU’s are sent out all ports including the backup and alternate for each Hello Period. How this feature works ...
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1
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How to prevent loop while trunking Fortigate and Cisco L2 Switches
I have inherited a rather weird setup at work, although my forte is servers and cloud, I have to look into network matters as well due to lack of resources.
This setup has 2 x Fortigate 100Ds (FG1, ...
user29422
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1
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132
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can a switch participate in STP without MAC?
I was wondering if my switch that doesn't have MAC addresses assigned to any of its customer ports can even pareticipate in spanning tree protocol negotiations?
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4
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Block L2 Loops without STP?
I have a weird problem: I have a layer 2 network that does not pass STP BPDUs and cannot be configured to do so. I would like to establish multiple redundant connections to this network from my all-...
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1
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Cisco Layer2 ACL and STP
i created a Mac-ACL on a unch of 2960X Switches to limit user access to the internet-gateway only.
mac access-list extended PROTECTED
permit any host ffff.ffff.ffff 0x800 0x0
permit any host ffff....
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2
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How fast can STP, RSTP, and MSTP find a new route?
If I have two switches connected redundantly and both are capable of using STP, RSTP, or MSTP, how quickly can an alternate route be detected and normal communication resume if the main route is ...
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Does the System ID Extension ever affect root bridge election?
In the STP Bridge ID (BID), the original, two-byte priority field was split into a four-bit configurable priority and twelve-bit System ID Extension (SIE) to represent the VLAN. Therefore, the ...
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1
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RSTP Vs STP Vs MSTP
I am sure this is a common question but would like to know the best practices. I have a pair of Juniper routers connecting to a IRFed HP 10k core switch. My HP core runs stp and we are tyring to ...
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2
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Edge port continuously switching between Port-offline and blocked by STP
I have a computer1 connected to ip phone which is connected to an HP J9625A switch like this:
switch <-> ip_phone <-> computer1
l have been continuously receiving snmp traps close to 10000 ...
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3
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Bridge is always root for a vlan
I have a switch that is not receiving BPDU Hellos properly and I have not been able to pin point the problem. Switch 1 puts all ports for vlan4 into desg mode and claims it is the root for vlan4 (the ...
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How did I break (half of) my network?
I'm looking for some post-event advice so this event doesn't happen again.
We have a network core of two Cisco 4500x switches, configured for VSS redundancy. From those, we have iSCSI devices, our ...
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1
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Switch is not sending BPDUs back in native VLAN (different from vlan 1)
I have two Cisco switches connected with two trunk links.
On the first switch spanning tree is switched off.
On the second switch, MST is turned on.
Ports configuration is as follows:
interface ...
