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.
3
votes
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 ...
4
votes
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 ...
4
votes
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. ...
1
vote
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 ...
2
votes
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 ...
2
votes
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, ...
2
votes
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. ...
5
votes
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.
...
4
votes
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 ...
1
vote
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.
1
vote
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 ...
2
votes
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
votes
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
votes
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
votes
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 ...
1
vote
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
votes
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 ...
1
vote
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
votes
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
votes
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 ...
1
vote
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
votes
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 ...
2
votes
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
votes
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 ...
2
votes
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
votes
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 ...
0
votes
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.
2
votes
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 |===|...
5
votes
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 ...
0
votes
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
votes
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. ...
1
vote
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 ...
1
vote
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 ...
1
vote
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
votes
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
...
1
vote
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 ...
1
vote
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
votes
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.
1
vote
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
votes
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 ...
1
vote
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
votes
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 "...
0
votes
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)...
0
votes
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
votes
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 ...
1
vote
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.
1
vote
2answers
57 views
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.
2
votes
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 ...
2
votes
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 ...
0
votes
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 ...
