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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Should portfast be used on a port potentially connecting to an unmanaged switch?
I understand the basics of how spanning tree works and why you would want to use portfast on user access ports.
When dealing with a topology with a large number of dumb switches under desks and ...
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3
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How is the root bridge elected in STP?
How does STP/RSTP determine which bridge is the root bridge, and how are paths to the root bridge selected?
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Should i run UDLD with spanning tree?
Can spanning tree and UDLD be run together, and if so, is this a good idea?
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14
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2
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STP blocking port selection
I want to make sure I'm understanding how this works. Specifically the term "Sending Port ID" has me very confused.
Consider this diagram, I want to make sure I have root port selection figured out:
...
- 459
12
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2
answers
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Tracing TCN Messages in STP
We have about 20 vlans on a L2 network running Rapid PVST+ where the root bridge is a stack of Cisco's 3750 switches. I am a bit puzzled by the number of TCN notifications I receive on the switch..
...
- 894
11
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2
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Preventing STP loops in etherchannels configurations
What is the best practice when configuring etherchannel on Cisco switches to prevent a STP loop/broadcast storm when etherchannel is mis-configured?
I had an instance where 2 ports on a switch were ...
- 2,535
11
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1
answer
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How can I make a PVST+ switch root towards MST network?
In a network where the majority of the switches are running MST but a select few are still running PVST+, how can the PVST+ switch be configured to be the root of the spanning tree? Topology below:
+-...
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11
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2
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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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3
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Spanning tree Default Priority Values
This question is a repost of the same question in The Cisco Learning Network; however, the answers are unique to Stack Exchange.
I have always accepted that the defualt priority value of STP (802.1d) ...
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10
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4
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Should spanning tree path costs match on a physical link?
While working on a set of switches I noticed that the spanning tree path costs aren't set up to match on opposite sides of the same physical link. For some reason that doesn't look right to me. ...
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10
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5
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RSTP: Using switches in pairs to two switches?
I am trying to set up the following arrangement with 10 switches:
I think it's relatively self-explanatory, but basically I have 8 different networks (in 8 separate VLANs) which are physically ...
- 101
9
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3
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I have a single ethernet switch. Should I use spanning tree?
I have a single ethernet switch. Should I use spanning tree?
If there is a redundant link, definitely need to enable STP.
In a single switch, how is it possible to have a redundant link?
Any other ...
- 155
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3
answers
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Does Switch need its own MAC address?
I saw a post say Switch do not need its MAC address, unless it's an administrable Switch for managing.
but I found the spanning-tree protocol need a MAC address of Switch to form STP Root Bridge ID. ...
- 813
9
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1
answer
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RSTP vs. STP it really sounds just a big ball of semantics? what's the main difference between them?
one difference is that Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) assumes the three Spanning Tree Protocol (STP) ports states Listening, Blocking, and Disabled are same (these states do not ...
- 425
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1
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EoMPLS, MSTP, and RPVST
We are looking at Cisco ME3600 to provide connectivity between our datacenter fabrics for some software defined networking. Due to the platform having a higher limitation on EoMPLS xconnects than ...
- 1,170
9
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3
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3k
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Trying to test a virtual lab VRRP configuration for STP issues
I'm in the middle of setting up a lab with a VRRP configuration, and I'm trying to search for any possible issues we might run into in production.
One issue I am aware of with VRRP is that it seems ...
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8
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2
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Will STP lose data whilst switching from a failed link?
In a network with a dual-redundant link between two switches, will any data be lost during the switchover from an active link to the blocked link when the active link fails?
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MST Spanning Tree BPDU`s
I know that MST using regions so that it doesn't have to run multiple instances of spanning tree.
However on a trunk are the BPDUs no longer tagged (dot1q) and sent to the neighbor device. i.e are ...
- 269
8
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1
answer
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Migrating from STP short mode to long mode?
It was decided recently to migrate a large campus network from the short mode STP costs (16-bit) to the long mode STP costs (32-bit).
I have clearly found it documented that this needs to be a "...
- 27.1k
8
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1
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Native Vlan Cisco Catalyst and Layer 3 switch
I have run into an interesting issue setting the native VLAN between one of my Cisco Catalyst 2960 and my Layer 3 switch (third party). Here is the setup, the layer three switch is set up to run on ...
- 403
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2
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Cisco 2960 Portfast ports generate Spanning Tree TCN
We are operating several Cisco 2960S stacks here and, for some time, are experiencing regular Spanning Tree TCNs (Topology Change Notifications).
When using show spanning-tree detail to get to the ...
- 440
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2
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RSTP Basics: Can this be done?
What I've got:
Two 24 port switches in building A, with 2 fibre trunks from building A to building B - where there are two 48 port switches.
The two 24 port switches support RSTP and STP. HP 1810-...
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Are multiple links with different VLANs between two switches possible?
I'm not considering Etherchannel or LACP.
Given 2 Ethernet switches A and B, where both switches have port 0 configured as a tagged trunk for VLAN 100 and 101 and port 1 configured as a tagged trunk ...
- 763
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votes
1
answer
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Mixing Cisco STP Features: BPDU Guard, BPDU Filter, PortFast and PortFast Trunk
I have two switches (Cisco 2960's) with a trunk between them (two ports in an ether-channel) and each has a trunk up to a separate router, all other switch ports are access ports to end devices;
R1 ...
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1
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MSTP and Rapid-PVST+
We have a medium sized network running all Juniper except for one building. This building is shared with another group, and is completely Cisco. We just trunk our VLANs up there.
Our Juniper network ...
- 73
7
votes
2
answers
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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 ...
- 1,015
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4
answers
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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
7
votes
3
answers
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How do I configure a port as STP "non-edge" on Juniper EX switches?
Juniper EX switches automatically categorize a port as an spanning-tree "edge" (there should only be one device behind the port) or "non-edge" (another switch) port. You can force this mode for a port ...
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7
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Uplinkports between two Cisco stacks gets blocked by RSTP
I should get this figured out by my own, but actually I seem to be a blockedhead.
I have two stacks of Cisco 3750X with two switches in each stack. One Stack is in building A, the other one in ...
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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,...
6
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1
answer
398
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Spanning tree question
I have the following setup:
Distro Switch 1 <-> Distro Switch 2
||
||
Access Switch
One cable is going from port 47 to Distro switch 1 and another ...
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6
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2
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STP Packet on specific interface eth1
I have an issue related to some stp packet that being sent every 1 or 2 second on my server interface eth1.
This interface is connected to my stack switch, and the port is in a public vlan.
Here is ...
- 117
6
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3
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LACP from Cisco 6509 to Force10 S48-10 - in default VLAN1
A client has the following configuration:
The entire network is on VLAN1, with the subnet 172.16.0.0/16 - performing a redesign of their network is not an option at this point, as they're a 24/7 ...
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6
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2
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Converting to extended STP system-id
We have some Cisco switches running PVST. I need to convert them to use extended system-id so I can use high numbered vlans.
The Cisco stp docs say
When you enable or disable the extended
...
- 185
6
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1
answer
608
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Spanning-Tree debug logs C7600
I am trying to debug STP on a C7613 but I have logging issues.
IOS version 15.2(4)S2
The Route Switch Processor is RSP720-3CXL-GE
I'm running every debug commands for Spanning-Tree but nothing gets ...
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1
answer
404
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Odd stp issue on foundrys
I have 2 foundry devices running 802.1w which are both connected to an access switch which also runs 802.1w.
The 2 foundry's are connected to each as well.
I have the vlan configured on each of the ...
- 1,378
5
votes
5
answers
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Spanning Tree between only 2 HP switches connected via Etherchannel?
Had my first experience with HP switches (2x ProCurve 2810G) and I realized that STP is not enabled by default. I discovered this only after having already configured an Etherchannel with 3x1Gig-Links ...
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Do layer 3 protocols use layer 2 protocols?
I saw the STP on layer 2. The guy that made the tutorial says at the end :
Even though it seems that Layer 2 access layer solutions are slowly
being replaced by blazing fast Layer 3 solutions.
...
- 163
5
votes
2
answers
708
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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 ...
- 153
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When connecting 3 switch in Spanning tree, Should I use Switch port or SFP ports?
I have 3 Cisco switches. Should I use standard switch ports or SFP ports for spanning tree? What are the benefits to using the SFP ports?
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Connect 3 Cisco switches via ethernet ports?
We have been using 2 Cisco 2960-S 48 Port switches which were connected together using a regular Cat5e cable and everything was working fine, however we have purchased a 3rd switch of the same model ...
Jon Davies
5
votes
2
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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:...
5
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2
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spanning tree RootGuard question on vPC switches
I have following diagram and two distribution switch connected back to back over vPC
Related spanning-tree question is it ok to use RootGuard on both distribution switch where access switch is ...
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1
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When and where to use Spanning-Tree (Portfast)
The tl;dr, in which scenario (switch-to-host, or switch-to-switch) do I use spanning-tree portfast or spanning-tree ...?
We had a catastrophic network outage today. My first question to my boss was "...
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Spanning Tree protocol question
Assuming there are three switches interconnected(Switch1--Switch2---switch3---switch1) to each other and STP has convergence has taken place and there is no change in the topology for a while. Now my ...
- 321
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3
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How to extensively test an ethernet switch
I have a Cisco SG200-26, and it appears to cause random network problems like timeouts, etc. Error logs on the switch do not indicate any problems.
I replaced the switch with a different switch, and ...
- 51
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1
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Is Per Vlan Spanning Tree or RPVST an open standard or can it only be implemented by Cisco?
I know there are some standards that are CISCO proprietary but have become open standards. CISCO has also updated the RFC to reflect this. So, is this also true for PVST?
Does Juniper or other ...
- 181
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1
answer
991
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How can I determine the STP designated bridge on Cisco IOS?
I am working with both older Foundry switches, and Catalyst 3560s, and trying to document the spanning tree topology. The Foundry switches show me the root port and root bridge as you would expect, ...
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How does STP convergence work?
Consider the IEEE 802.1D (first revision) Spanning Tree Protocol. I have read a lot of articles and forum entries about STP convergence. Often I do find contradictions about the convergence mechanics. ...
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Which switch MAC addresses are used for the Bridge ID in STP?
Lets imagine that I have big LAN environment with many switches and many VLANs, for example, VLANs 5,15 and 50. I have PVST+ activated, and all of my switches have same (STP) priority.
I connect a ...
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