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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23k views

Multiple spanning tree terminology (CST/IST/CIST) and exact behavior

I have the feeling the more I read about MSTP, the more confused I get. So here we are in order to make things clear once and for all. http://www.cisco.com/c/en/us/td/docs/switches/datacenter/...
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1answer
393 views

In RSTP, does port have a state when there is no link on it?

As we know, RSTP merges "disabled", "blocking", "listening" states of STP into one "discarding" state. However, when a port is linked down, let's say no physical link on the port, is there still a ...
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2answers
1k views

Netgear SFP and trunking between three switches

Can you use SFP stacking with trunking? We have two Prosafe S3300-28x switches stacked using two SFP cables. These switches also have two 10Gig ports, which we would like to connect to a separate ...
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1answer
2k views

LACP trunk between BNT layer2/3 switch and Cisco 2960s stack on a bladeCenter H

My objective is to replace a Nortel 5520 stack with a stack of Cisco 2960s. The old working configuration was using mlt trunk between 5520 and BNT layer 2/3 switch. I will use LACP for the trunk ...
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3answers
398 views

Spanning Tree -DesignatedPort

What's the interest of Designated Port in STP algorithm ?I didn't get their goal,we have both RootPort and DesignatedPort
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0answers
627 views

proposal flag and agreement flag in 802.1w RSTP BPDU packet

For my current understanding of RSTP, the proposal flag and agreement flag should not be set to "1" at the same time, and they should also not be set when the network topology is stable, which means ...
3
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2answers
387 views

UDLD on Nexus 5548 and Nexus 2232

Do you know if I turn on UDLD the 5K and 2K will speak UDLD to each other and do you feel this is a benefit to detect any link issues between the 5K and the FEX? Thanks
3
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1answer
148 views

Why use one MAC per port design in L2 switch for STP function

While I'm testing the STP function in several different Switches, I found Some Switches use single MAC address for all LAN ports (e.g. Buffalo's BS-G2108M, Netgear's GS716Tv3), while some other ...
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1answer
4k views

Does the spanning tree protocol come as standard in L3 switches? [closed]

Online there is a lot of content mentioning the spanning tree being a l2 switch feature so I guess it comes as standard/ is a given that it available for all modern l3 switches... (Could the answer be ...
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2answers
1k views

Blocking all VLANs between Juniper switches

I have some Juniper switches (Model: ex4550-32f) connected together with trunk ports. I want to allow VLAN 6 on all below interfaces because it is the main switch and connected to other switches in ...
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1answer
2k views

Link aggregation: disable spanning tree

It's a simple question, with switch interfaces using etherchannel,is necessary to use bpduguard in these interfaces for that disable Spanning-tree? Because using mode simulation of Packet Tracer, I ...
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1answer
656 views

How Forward Delay Timer is estimated in Spanning Tree Protocol

From my understanding so far, to estimate forward delay, the following formula should be used. (end-to-end_bpdu_propagation_delay + message_age_overestimate + tx_halt_delay + max_frame_lifetime)/2 (...
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1answer
2k views

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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4answers
936 views

Trunk link between Cisco switches does not allow internet to the end users

I have a issue in my network. In terms of OSI I am OK in the physical layer. My link is OK because I tested connecting a computer on a fiber link, and I was able to surf the Internet, but when I make ...
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2answers
2k views

Spanning-Tree Interoperability between ProCurve core & Cisco access layer

I need help regarding the following spanning-tree issue. I have a network core of 2 HP5412 (procurve) connected together using VRRP over a L2 tagged link. I have a Cisco 3560 connected to each of the ...
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1answer
6k views

how to read the STP status (FORWARD/BLOCKING) of each interface/port via SNMP

how can I read the STP port status of each interface (in my software/program)? There is a MIB called BRIDGE-MIB with OID "dot1dStpPortState=1.3.6.1.2.1.17.2.15.1.3" that returns the FORWARDING OR ...
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1answer
135 views

PVST with VLANs not matching on switches

How will PVST behave in a situation in which there are two switches connected to each other via access switchports which have different VLANs assigned to them? Ex: [Switch 1] Port with "Access Vlan ...
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2answers
5k views

Set priority of bridge to 0 but root bridge shows now priority 1 in STP

I have configured a network in Packet Tracer with 5 switches and connected them all together. Then, I configured a priority of 0 and wanted to see how the election of the root bridge takes effect. ...
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1answer
2k views

Will STP portfast prevent a loop?

I'm trying to understand if two ports on the same switch, are in portfast mode, will a loop be created when the two ports are connected to each other. i.e. if FastEthernet 0/2 and 0/3 are both set to ...
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1answer
166 views

Behavior about 802.1D with ISL

Reading this quote, The 802.1Q standard defines one unique Spanning Tree instance to be used by all VLANs in the network. STP runs on the Native VLAN so that it can communicate with both 802.1Q and ...
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1answer
2k views

Setting up a new Meraki MS220-48FP Switch to replace a pre-existing DellForce10 Switch

I have a new Cisco Meraki Switch that is replacing a DellForce10 switch that is already in place. I need to configure the Meraki switch to how the Dell switch is setup. The only thing that is ...
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0answers
2k views

Block MSTP on port Dell N series networking

I am noticing that our Dell N4000 series switch connected to a stack of Cisco devices is constantly attempting to change spanning tree topology. The Cisco switch is our Internet connection and a fiber ...
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1answer
2k views

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 ...
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1answer
488 views

Interoperability CST and PVST

Per-VLAN Spanning Tree+ (PVST+) is an extension of the PVST standard. Per-VLAN Spanning Tree+ (PVST+) allows interoperability between CST and PVST in Cisco switches. What does interoperability ...
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1answer
2k views

Cisco proprietary protocol - Spanning Tree

I was reading a wiki page about Spanning Tree and the following quote intrigued me: "Both PVST and PVST+ protocols are Cisco proprietary protocols, and few switches from other vendors support them. " ...
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1answer
87 views

Current Mode Spanning Tree

What is the current mode Spanning Tree running on Switches, since 802.1W was incorporated into 802.1D-2004? Even being 802.1D or 802.1W still not support VLANs, just Native VLAN has one SPT instance?
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2answers
2k views

Juniper trunking with two links (not using LAG)

Some reason I'm drawing a blank on this. Let's say I have two EX switches connected together with 2 links to each other (xe-0/1/0 and xe-0/1/1 on both switches). I can easily setup a trunk on one of ...
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2answers
585 views

Avoiding switch loop?

Please advise on the following question: With 2 Cisco 2960G switches connected as in the diagram: STP is not used. How could the switches be configured in such a way that all the traffic HOST<-&...
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1answer
6k views

Why showing IEEE Spanning Tree protocol

I'm preparing for the CCNA and I have a little trouble understanding the outputs for STP. By default a CISCO switch use PVST (Per VLAN Spanning Tree) but if we use the command show spanning-tree ...
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1answer
109 views

AP High latency, sometimes disconnection from network [closed]

I have 6 APs connected to a desktop switch http://www.tp-link.com/lk/products/details/cat-4763_TL-SF1005D.html MY APs are TPLINK TL-901WD The desktop switch is connected to my main router Asus ...
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2answers
19k views

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: ...
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2answers
131 views

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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2answers
202 views

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 ...
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1answer
3k views

Why am I not seeing a spanning tree instance?

i86bi-linux-l2-adventerprisek9-15.1a.bin on Cisco IOU via GNS3 I set up the following topology in GNS3: All I did was power on the devices, connect them and do a 'no shut'-command on their connected ...
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1answer
3k views

Configuring RSTP and LACP. Unplugging a LACP port causes a topology change and pauses all switch traffic

I am having trouble with configuring LACP and RSTP on a (TPLINK TL-SG3424) switch. If I reboot the VM Server or unplug one of the LACP ports it causes a RSTP topology change that pauses packet ...
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3answers
118 views

portfast uses enabled does not producing loop [closed]

I want to know how a portfast will cause loop. I tried connecting a switch with portfast . As soon as another switch connected it enter to normal switch and has the block port.
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1answer
975 views

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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2answers
1k views

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 ...
3
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1answer
741 views

Does the Juniper SRX have spanning-tree capabilities?

I can't find any documentation supporting spanning-tree capabilities on SRX devices. I'm running a virtual image, which I thought was more-or-less the vSRX: root> show version Model: ...
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0answers
185 views

Overlay network with GRE without spanning tree [closed]

I need to create an overlay network with potential of hundreds of servers (each is an hypervisor and running a open vswitch). I'm going to use ovswitch and connect each server to all other servers ...
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2answers
1k views

STP load balancing

Topology: sw3560 gig0/23 ---> fa0/24 sw2960 sw3560 gig0/24 ---> gig0/2 sw2960 I have a question regarding to STP load balancing, on my switch 3560 I configure the following: ! interface ...
3
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1answer
278 views

Identifying Designated port in STP when Cost and BID are the same?

I am having trouble on how should I identify which port will be blocked and which will be the designated, since both BID and Cost are the same for the ports. Now for first port, the output of show ...
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3answers
6k views

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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2answers
2k views

How do I stop %C4K_EBM-4-HOSTFLAPPING message for wireless ports, but leave on for STP issues?

I do not have a spanning tree loop. I work in a manufacturing environment and roaming is prevalent. I don't want to see mac flaps or host flap messages on the wireless ports, I only want them for STP. ...
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3answers
9k views

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 ...
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2answers
978 views

STP Needed with this layout?

Having difficulty grasping STP and if we would need it with the topology we have. The diagram is a top down view of our layout, and each "layer" is a different building connected by fiber, orange ...
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2answers
1k views

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 ...
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1answer
1k views

Juniper EX Flooding on STP Topology Change

I have a relatively large layer 2 network where port flapping is not uncommon. I am using Juniper EX 2200 switches, which clear out the mac-forwarding table on a topology change. It is not uncommon ...
4
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1answer
744 views

Cisco / Spanning Tree on Access Ports from ISP

Please excuse my ignorance & noobishness. I have a switch which has two different point to point connections, these both plug into access ports & have their own VLAN. These two point to ...
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3answers
8k views

MAC Flapping on Cisco 2960G

We've been having an issue for the last few weeks on a relatively small network. The issue started when we swapped a specific Cisco 3750 for a 2960G (there were some other changes), exactly since then ...

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