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Questions tagged [spanning-tree]

For questions about Spanning Tree Protocol (STP), originally defined by IEEE 802.1D, to prevent bridge loops at OSI layer-2.

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1answer
40 views

Cascading a switch interface to another switch

We have a service provider switch which has an interface that we use to connect to other users over. We have been advised by the SP that we can use this interface how we wish (i.e. feed it into a ...
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2answers
144 views

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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1answer
198 views

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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1answer
85 views

PVST + MST + RSTP network. Possible to make it work?

I have got a network (around 100 switches) which looks like this: Cisco 2960 - can do PVST, RSTP, MST MRV mr2228-s2c - can do STA, MSTP HP 1810 - can do RSTP, STP Two main Ciscos are linked with ...
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2answers
84 views

OpenvSwitch Spanning-tree priority for specific Vlan ID

I'm new to the SDN technology, I have 12 year's experience working with Cisco products, On Cisco devices, a user can set different STP priority Per VLAN ID Like : Switch(config)#spanning-tree VLAN ...
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3answers
61 views

Are the Switches not direct connect to the root-bridge need select root port in the STP circuit?

In the STP circuit like bellow, will the Router2 select a root port? or just the Router1 and Router3 select root port? in a tutorial it says "all the non-root bridge node will select a root-port, ...
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2answers
57 views

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. ...
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4answers
989 views

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. ...
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2answers
397 views

Spanning Tree on the interface that resides at end users

I do not understand why we use portfast and in fact STP on the interface of a switch that is directly connected to end users. Indeed, a user can interfere with the STP election and perform DDoS (that ...
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1answer
34 views

Does STP create a minimum spanning tree?

From the algorithm described in P&D textbook it looks to be minimum (if all edge weights are 1). Can't find mentions on Wikipedia or a quick google search.
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1answer
87 views

Spanning-tree MSTR port role

What is the MSTR port role in Spanning-tree ? It shows up on boundary ports between MST regions and switches running (R)PVST+. Note that it shows up only on the switches running MST. It seems to ...
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0answers
43 views

How to set portfast default on Dell FTOS Switches?

I'm configuring a Dell S3148 switch running FTOS 9.14.0.1 and I would like to achieve similar functionality of the following Cisco IOS commands: spanning-tree portfast default spanning-tree portfast ...
3
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1answer
177 views

How to solve a BKN* Port Issue on a cisco catalyst

There is a Cisco ISR 4451 connected with Portchannel to a Catalyst 3850 Stack and there are some VLANs enabled, but only one does not come up for a Portinconsistence. I figure out an Issue on the ...
2
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1answer
65 views

As a Spanning Tree Protocol Programmer, how will I know when the root bridge ID election is over?

I am trying to implement IEEE 802.1D. I know how the root bridge id is elected. Initially, every switch will advertise that they are the root bridge. Next, it will check whether the bridge ID received ...
5
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1answer
326 views

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 ...
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2answers
189 views

spanning tree loop with bpdufilter on acces port but not on trunk?

┌─────┐ ┌─────┐ | A ┼------┼ B | └─────┘ └┬───┬┘ └---┘ <-- loop behold the above drawing. this is a test setup connectin switch A and B, and a test loop A: cisco ...
5
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1answer
158 views

How to resolve a spanning tree issue on a server trunk port?

I am having a very strange spanning-tree issue with Cisco Nexus switches. My server is connected to the TOR switch with trunk configuration because we have multiple VLANs on the server. When I reboot ...
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2answers
166 views

How should (per-vlan) STP behave when interconnecting access ports from different vlans on the same switch?

Half of the ports of a switch are in vlan 10, the other half in vlan 20, all untagged. In some specific situations, we need someone in the field to be able to interconnect both vlans without access to ...
3
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1answer
166 views

Add links to a port channel group without downtime

There are two trunk links with the same configuration connecting two switches. Currently they are independent links and one is blocked with spanning-tree. I would like to convert these to a single ...
2
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1answer
59 views

Spanning tree behaviour - topology change

Regarding a next change we have to do, we are studying spanning tree behaviour. Does the following statement is true ? In the case of topology change, if a new BPDU is received: Currently: Root ...
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1answer
51 views

Replacing a pair of switches and stp

We need replace to a pair of switches with new ones without interrupting traffic. In order to do that , for some minutes all 4 switches will be interconnected between them - but we need to avoid stp ...
2
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1answer
42 views

Edge detection on designated ports

If a switch doesn't receive a BPDU on a particular port it marks this port as "Edge Port". But any designated port won't receive any BPDU even though it was connected to other switches since their ...
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2answers
181 views

redundant vpn to remote location with redundant links

I have this situation: Remote location with 6 devices collecting data and each connected to two VPN routers. Bonding is set up for those computers and data is sent to multicast address. Each VPN ...
3
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1answer
104 views

Does a bridge have the three STP timers per port or per bridge (one per bridge)?

I was trying to understand Spanning Tree Protocol and I got confused on some points, so I want to ask for some and double check for others: Do the three timers(including max_age) exist in the bridge ...
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2answers
79 views

I CAN'T ping PC7

So... I have a set up as below. I ping PC7 from the router. obviously an ARP is sent to determine PC7's MAC address. but it doesnt work. i then decide to set packettracer to simulation mode. i ping ...
2
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1answer
91 views

Best way to connect Vlan's / STP / LAG

Am having a problem connecting these concepts together , like when i try thinking of them being ran on the same network. am able to understand each of them separately, But am not able to connect them ...
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1answer
604 views

What is the EtherType of a BPDU frame sent by a switch which runs Spanning Tree Protocol

I want to know what is the EtherType field of a BPDU frame in various versions and variants of the Spanning Tree Protocol.
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1answer
838 views

Bridge Assurance with vPC on port type network

I'm running two Nexus 3048 switches as network core and I got an issue when linking another switch (specifically a 2960-X) on the vPC links. Consider the scenario: +-------+ +-------+ | NX #1 |===|...
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2answers
331 views

High availability LAN segment with Cisco ISR4451X and 2 x Netgear GS724 - Port-channel vs. BDI vs. BVI?

I have a customer that is getting a new 1Gbps ISP connection and wants his servers connected across two switches for redundancy and protection from: failure of a router port failure of a network ...
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0answers
35 views

Consequences of changing spanning-tree timers on core switches on live network

I have recently been replacing some of our old switches and found that there are topology changes spamming the logs. After some investigation I have found the spanning-tree timers on the core switches ...
2
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1answer
59 views

Trying to configure STP on a small network and have a few questions

I am trying to configure the switches on a network to use STP or RSTP but I'm confused about how to do this. The network consists of 3 switches, all on the default subnet, so a fairly simple setup. ...
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2answers
290 views

What could cause network to duplicate packets? STP during convergence?

I have understood that real networks have routing changes, leading to out-of-order delivered IP packets. Real networks also have frequent packet loss. However, what I have not understood is why could ...
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1answer
388 views

Cabling two access ports on the same switch from different VLANs

Theoretically would I be able to connect two switch ports together with a simple straight/cross cable on the same switch. If the two ports are in different VLANs (eg. 2 and 22) and ports are in ...
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1answer
191 views

root port election in STP

I have a question about root-port election in STP. How to determine root-port on switch 3, both fa0/1 and fa0/2 have port-cost back to root switch (switch 0) of 38, receive BPDU from port fa0/3 of ...
2
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2answers
137 views

MSTP - different VLAN mapping in different regions

Regarding MSTP, is it possible to have different VLAN mapping for different regions ? Example: Region 1: Instance 1: VLAN 10,20,30 Instance 2: VLAN 40,50,60 Region 2: Instance 1: VLAN 10,50,60 ...
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0answers
213 views

Adding new switch to Spanning Tree network

Currently studying Spanning Tree, I'm not sure about the behaviour when we add a new switch to an existing STP topology (with cisco pvst+). Assuming we plug this new bridge called S4 with only one ...
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3answers
143 views

Doesn't a router stop broadcast?

Well I was at work. And one of our customers connected a new device to that router. Additionally a switch was already connected to the router. So there was only the switch connected to the router, ...
2
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1answer
241 views

Rapid Spanning Tree Protocol - RSTP Bridge Id isn't RSTP-Priority + Ethernet-MAC

what is the difference between the eth.src Address and the Bridge-System-Id? Sometimes they are the same but mostly not. Attached you will find a screenshot where they are the same.
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1answer
232 views

Why forward delay in spanning tree

I would have a really basic question... Why the spanning tree have forward delay ? (listening=15s and learning=15s). Why initially the protocol has been designed like this ? 30 seconds before ...
2
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1answer
246 views

Spanning tree - port roles and status during root bridge election

Regarding my studies I would like to confirm the three statements below about spanning tree. When a switch boot or spanning tree is enabled on a switch, the switch ports pass into blocking state 20 ...
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2answers
240 views

Spanning tree root bridge process validation

A question regarding the spanning-tree protocol. During the root bridge election process, how is the end of the election validated? In other words how does the spanning-tree protocol know when the ...
5
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1answer
2k views

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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1answer
347 views

Does a switch generate TCN BPDU when it elects a new root bridge?

what are the scenarios in which a switch generates a TCN BPDU other than when a port goes down or come back up? switch-1---------------switch-2----------------switch-3 (root bridge) (Non Root)...
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1answer
41 views

Possible to do a port-channel and STP with three 10Gbps fibre interfaces?

I have two sites that I'm planning to interconnect via three circuits carrying layer 3. They will be presented via fibre. The bandwidth of the lines will be: 1Gbps, 1Gbps, and 2Gbps. Each SFP will ...
3
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2answers
427 views

BPDU exchange between RSTP switches

According to the documentation: BPDU are sent every hello-time, and not simply relayed anymore. With 802.1D, a non-root bridge only generates BPDUs when it receives one on the root port. In fact, a ...
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1answer
3k views

PVST, PVST+ and RPVST

what are the port states and port roles for the following: PVST, PVST+ and RPVST? I did some digging. still, I didn't find an answer to my question.
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2answers
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Are TCN BPDUs dropped on their way to the root if “message age” gets higher then “max age”?

Normal BPDU gets discarded if the message age field reaches max age. I'd like to know if it's the same for TCN BPDUs on their way up to the root bridge.
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1answer
117 views

What happens when a BPDU message age reaches “max age”

I read that every time a BPDU is forwarded by a switch, the message age is incremented by 1. Also the switch will wait "max age" - "message age" for a new BPDU. I'd like to know what happens if a ...
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2answers
309 views

Can't get DHCP to work in Spanning Tree

I'm not entirely sure what I'm doing wrong. I configured the inter-VLAN routing from the main router with the IP addresses I used as default router for the DHCP pools I also set in the main router. I ...
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4answers
473 views

STP not preventing switching loop

I have a TP Link managed switch that I have enabled STP in, but it's not detecting a loop in the network, and brings the entire lan down. I plug two ends of an Ethernet cable into the switch, which ...