Cisco :: Core Layer Switches After A Spanning-tree Topology Change Occurs
Mar 24, 2013
I've been taught/under the impression that vlans and stp stay in the access layer to prevent bridging loops and broadcast storms from taking down the whole network. Well I was reading about backbonefast and how it "Enables fast convergence in the networkbackbone or core layer switches after a spanning-tree topology change occurs." Now I thought that from the distribution layer up we use a routing protocol.
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Apr 9, 2012
My colleague and I have been having a discussion about using rapid spanning tree in the access layer. Most of our infrastructure has been migrated to a routed access layer with 3750s.
The idea was brought up to configure the switches with rapid PVST. On the surface, it seems like a better idea, faster convergence, in the event that spanning tree ends up being used for some reason. My colleague prefers sticking with standard PVST. His argument is that, in the event of a layer 2 loop, some consumer-level switches filter out BPDUs and if the control plane is overwhelmed, the shorter timers of rapid PVST just puts that much more of a burden on the CPU trying to regain control, whereas with standard PVST it will have around 20 seconds before it starts to engage. (It may still be overwhelmed, but the longer timer delays the additional burden.) He says he's seen this problem with rapid PVST and that his opinion is backed up by our Cisco rep. (I haven't spoken to him yet.)
In our model, it should be very rare -- pretty much never -- that we would layer 2 span another switch off of our access stack.
One suggestion I saw is to use BPDU Guard, which is a good suggestion as well.
But we have had experiences with overloading the control plane on a 3750. I believe that concern is valid. If the CPU can't service spanning tree. But I'm interested in hearing about other experiences people have had in terms of rapid spanning tree in the access layer, end users plugging in unauthorized devices and creating loops, and the effects when using rapid spanning tree vs standard spanning tree.
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Jun 19, 2012
changing the Spanning-tree mode on a live 6500 running in a VSS mode?If so what are the things to watch out?
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Aug 20, 2012
I have 2 switch groups.
2 SGE2010's with VLAN's defined as 10,20 and 30
Vlan 10 is the management VLAN, and it uplinks to our border router.Vlan 20 is the workstation VLAN, and all workstations point to the switch as their default GW? Vlan 30 is the ip phone VLAN, and all phones use this as their gateway.
I would like to put a LAG between said switches, we have some servers on the ip phone switch that need to be accessed by the workstation clients, and the single 100mb link through the router is probably not going to be enough.As I understand it, because the switches have different networks on them, a simple lag will not work. I did create a lag, and assign ip addresses to each side, however in that mode, it doesn't appear I can block vlan 10 from transiting the LAG, and with out that block I will end up with a logical loop, and spanning-tree will block one of the uplinks, or the LAG itself.
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Nov 18, 2012
Do switches learn link state information from routers and optimise the spanning tree between the switches accordingly ?
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Oct 25, 2012
I've got a bit of a query regarding how spanning tree works on L3 switches?So say we have a few 3550's connected together and spanning tree has converged and everything is looking ok. We then introduce routing into the network, does STP still operate in the same way or is this layer 2 feature now redundant because routing has taken over?I just couldn't figure out if STP still operates at layer 2 to prevent loops and routing sits on top to route the traffic?
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Feb 28, 2011
download speed is getting slower in lan, file and print sharing also take long time.
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Jan 8, 2013
I have a question in regards to configuration I'm planning to implement. I currently have 2 x 3750 running in a stack. I would like to add 1 x 870 router connected to both switches.It's important for me that 870 is always available (it will only be used as a backdoor for our management network through WAN) but I don't want it to participate in any switching (including switching for management network unless it's going through this backdoor WAN). Do I need to configure spanning tree on all switches or stack is automaticly working as a 1 logical unit?As router is only using 100MB/s connection, how I can prevent this router from switching packets with other switches?
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Jan 10, 2013
I have problems too when I connect 3com and Cisco.
I have 2 5500g 3com switches connected with 2 links. If LACP is disable, this causes serious problems and STP not works.
Logically , the link, is a port trunk with all the vlans permitted. One switch has STP enable and the other RSTP. Why this not works fine? I need to configure MSTP maybe? PVSTP is not allowed on this switches.
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Jul 21, 2012
We are upgrading out internal office network. I have setup 4 switches and 1 router using the following config.
-2 SGE2010p's are stacked together forming vlan 30 (to be used for phones)
-2 SGE2010's stacked for workstation's under vlan 20
Both switches are apart of vlan 1 (the default)Ports 1 on each stack are connected to a Cisco 890 (port fe2 and fe3) in trunk mode. Ports 2 and 3 are in an LAG group and connected to the neighboring stack (I have attached a diagram), and are also in trunk mode).At this point one port (port 1 on either stack) goes into blocking mode, and I get why ,it's a physical loop.I need more than a 100mb link between switches (which is what pulling the LAG between switches gets me), but I don't want to route phone traffic through my workstation switches to get out of the LAN.Is it possible using these switches and router to have a LAG between stacks and a link to the router for traffic to 0.0.0.0 ?
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Apr 11, 2013
Is there really any reason why you wouldn't use spanning-tree portfast on a trunk port other than a trunk between two switches? We have it enabled on all ports except for the fiber trunk between two non-stacked switches and the trunk ports connected to our Astaro firewall.I'd like to enable it on the ports to the firewall unless that would cause issues.
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Sep 29, 2012
I configure 3750 stack switch as core and 2960 stack switches as access layer switches.I connected my laptop to one of my core stack in VLAN 10 and I am pinging to one of my server in VLAN 1. What will be the minimum latency at the time of inter VALN routing
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Feb 14, 2013
I have setup a WiFi bridge using two Cisco 1262n AP. I was able to get the bridge up and running for a little while. But soon after I plugged in a switch on the non root side of the bridge, the LAN on the root side started slowing and user were getting disconnected from the network. I suspect the Spanning Tree issue with the Bridge.
Couple questions:
I am using both the 2.4 and the 5Ghz bands for the Bridge. I assume that this was OK and was needed to get the highest throughput, right?
I was making an assumption that the AP would take into account the possible spanning tree issues automatically when both bands are used in the same bridge. Is assumption correct? If not what is the correct configuration for spanning tree on a wireless bridge that uses 2.4 and 5 bands?
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Sep 6, 2012
For last few days I've been reading about Spanning Tree Protocol ,L2 protocol and understood how it prevents loop in network ,various steps in STP but one thing i wanted to know how STP actually detects the loops in network so that it can prevent it.Somewhere I read STP uses BPDU as probe and detects loops I mean how it happen is when switch send a BPDU with Destination Address as multicast and receive same BPDU again mean there is loop in network .But is it how STP detects loops in network?
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Apr 19, 2012
I am trying to confirm which of my cisco switch is the spanning-tree root. I know which I prefer to hold the spanning-tree and I ran the command spanning-tree vlan 1 root on this switch,I would now like to check that this command has worked and so I ran the command 'show spanning-tree root active' and received the detail below.To make sense of this and determine which port the mac address references (From this I take it that 00b0.d0f5.cf31 is the root, how can I determine which port this is).
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Jan 16, 2012
I need to implement a "Spanning Tree Status" view on my NMS and I would like to use SNMP. I'm running Rapid Per-VLAN Spanning Tree Protocol on 3560-E (WS-C3560E-24TD) with IOS 12.2(55)SE.Using the ciscoStpExtensionsMIB MIB (CISCO-STP-EXTENSIONS-MIB) I see the stpxRSTPPortRoleTable table, which contains the stpxRSTPPortRoleValue value, and I think it could be fine for my job.The problem is that this table uses an index based on the standard dot1dBridge.1.4 table (dot1dBasePortTable) that does not report some interfaces: [code]I think the dot1dBasePortTable does not include those interfaces (5, 7, 8) where I do not run standard STP, but I need the dot1dBasePortEntry entries because I have to use them in order to get the interface ID (values like 10109, 10110, 10111).
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Apr 4, 2012
Ages ago I was shadowing someone making a change on the network. I cannot remember which spanning tree version was running and cannot remember the config of any port either. What I do remember is that every switch port on the 2960 switch went orange and an outage occured, where the ports went into listening / learning mode. I assume that the STP was just the default ieee 802.1D.
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Sep 12, 2012
I am getting this error on our Cisco 5500 switch. What it means
2012 Sep 13 14:49:37 PDT -07:00 %SPANTREE-2-RX_1QNONTRUNK: Rcved 1Q-BPDU on non-trunk port 3/20 vlan 72
2012 Sep 13 14:49:37 PDT -07:00 %SPANTREE-2-RX_1QPVIDERR: Rcved pvid_inc BPDU on 1Q port 3/20 vlan 72
2012 Sep 13 14:49:37 PDT -07:00 %SPANTREE-2-RX_BLKPORTPVID: Block 3/20 on rcving vlan 72 for inc peer vlan 235
2012 Sep 13 14:49:37 PDT -07:00 %SPANTREE-2-PORTUNBLK: Unblock previously inc port 3/20 on VLAN 72
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Apr 24, 2013
I read that maximum spanning tree instance number is 128, is there any switches that can go more than128 instances ? or can we do this from IOS updates ?
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Oct 3, 2011
I have a pair of 3750-x switches stacked together. Using spanning tree with our upstream provider I have an active line in port GigE 1/0/25 and a blocked redundant line in GigE 2/0/25. I have setup a port based acl as below on 1/0/25 which is a port on the current master switch. Do I need to manually set this on 2/025 as well? Just wondering what would happen if the line to the master switch was to disappear or if the master disappeared completely whether the acl would automatically be applied to 2/0/25.
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Feb 29, 2012
I have a 3750 switch which has the command 'spanning-tree vlan **'. I am struggling to remove this command, as this particular VLAN is one I want to distribute across our network.I have so far, set the switch to VTP Transparent mode and removed the VLAN from the database, this removes the command. If I then put the switch back to VTP client mode (or manually add the VLAN, while in in VTP transparent mode) then the command comes back. Submitting the command 'spanning-tree vlan **' command has no affect.
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May 8, 2012
I want to have an opinion that which switch shall I replace the Cisco 2960s with so as to elimintae the need for spanning tree in there but then what would be the design look like between Netscreen and those new switches. Also would it be vendor independant to work Between Cisco and Netscreens/Cuberguard.
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Mar 21, 2012
..I am connecting a Nexus 5K to a 6509 without VSS. Is the recommended configuration just straight etherchannel? Since the 6509 cannot do vpc, is an etherchannel the best way to configure this uplink? How does spanning-tree operate.
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Oct 20, 2011
i can't configure "logging event spanning-tree" on a specific port under IOS 12.2.(58) SE2 (all other "logging events" are possible), under 12.2 (55) it is possible. Is it now a known bug or a default value?
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May 2, 2012
Recently we will add 2 new core Switch 3750X, these 2 equipments will manage the spanning tree ( root)my idea is to change the priority in order to make 1 or the 2 of them the root, my question is if i setup the same priority for both when one go down the other will assume the role of root in the spanning tree topology ?
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Mar 16, 2012
My SF300-24 switch has been working 100% as a backup switch for a client of mine. At my clients premises it was running 3 Vlan's and doing inter VLAN routing. When my client received their original switch back, I obviously brought my SF300-24 back to the workshop, reset it back to Factory defaults and tried to do a fresh installation on it. I can not get it to change from Layer 2 to Layer 3! I installed the latest firmware but still no go.
Everything works a 100% via the console, but when I go to the System Mode menu and try and edit it, it justs sits at layer 2 and will not chage to layer 3!
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Sep 19, 2012
Why is it when I set the port priority for example to 8192 and I then do a show spanning-tree vlan 1 it shows as 8193, does it add the vlan number? so if it was vlan 10 it would be 8202?
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May 12, 2013
I have two switches claiming to be the root bridge for the same vlans. The 3750-X stack was configured to be the root for vlans present and the 2960S was brought online over the weekend to replace another one. This is the command I used to attempt and make the 3750-X stack the root
spanning-tree vlan 1-2,10,50,101,200,900,999 root primary diameter 4
The IOS converted that to this
spanning-tree mode rapid-pvst
spanning-tree loopguard default
spanning-tree portfast bpduguard default
[code]......
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Nov 3, 2011
I am about rip and replace my current 3750G stack with a 3750X stack. I have trunked over vlan and vtp info and implemented a config so it should be ready to go other then moving cables onto it. However one thing I want to correct with our current setup is that the root bridge on our vlans including vlan 1 is on a separate set of switches that we control, however I would like this new stack to be the root bridge for all of our vlans. It will be the central set of switches that all other switches trunk into. I have pre-set higher spanning-tree priorities for each vlan on the new stack so I expect as I move lines into it that the tree will be re-calculated with it as the root bridge. I've ensured that there are no root guards on any of the other switches trunks and priorities are all at default levels for each vlan. Should I enforce root guard on the trunk interfaces of the new master stack? Most of the trunks are port-channels to the other switches - do I need to set root guard on the Port channel interface or on the individual ports that make up the Port channel? On both? Any other recommendations in regards to implementing spanning-tree with the new stack? I know using port channels eliminates a lot of potential for loops but not every trunk is and I'd still like to have spanning-tree on.
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Feb 8, 2011
A question concerning the use of REP for IE-3000-4TC switches:
In figure 14 of REP pdf URL can you explain why this creates a loop in the system? From the document, I thought REP and RSTP could talk to each other so why does this create a loop if they are exchanging information between each other? Also, if, in figure 14, the two switches in the STP domain that connect to the REP ring, were also connected to each other, would there still be a loop in the system?
Also, what is the recommended max diameter a REP ring should be. I thought I read some place 130 nodes is ok, but I'm looking to confirm this.
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Sep 25, 2012
I am looking for some troubleshooting for some Cisco blade switches that are running high CPU. I have two 3020 blade switches in an HP chassis that each have two 1G links port channeled a pair of Nexus 5548s. Spanning tree has been constantly running about 35% of CPU for the last couple of weeks causing management SVI latency and CLI lag. The Port channel is the root port and the switches have no other connections.
Here are the things I have tried in troubleshooting the issue.
-Remove links from port channel so that one is forwarding and one is blocking -Removed the blocking link so that the switch only has one uplink. -Converted from pvst to rstp -Entered no spanning tree vlan <all vlans> so when you do show spanning tree there are no instances of spanning tree-Connected the single uplink to a different switch
Nothing has changed the continuous high spanning tree utilization of about 35%.
The 3020 switches server interfaces are configured as trunks for ESX running on the blades. It seems the only possible loop that could be causing this issue is on the ESX virtual switches, but I am not sure how that is possible. I say this because I have another pair of 3120s that have the exact same problem! However they were working fine (CPU normal) until the enclosure was populated and began switching traffic. After they began carrying a medium/heavy network switching load, the 3120s are running at a constant 56% spanning tree CPU utilization!
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Aug 15, 2012
We will be connecting Cisco 4507 with Extreme Switches. We ran into spanning-tree issues last time. Extreme does not understand spanning-tree. So what i am thinking it to prevent bpdu advertisement from 4507 to extreme switches and also prevent incoming bddu from extreme switch to 4507. I am thinking of using
spanning-tree bpdu filter
spanning-tree bpdu guard
spanning-tree root guard
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Nov 9, 2012
I'm testing debug spanning-tree functions in a lab, hardware is Cisco 6509 with SUP-720-3B and WS-X6748-SFP, IOS is 12.2.33.SXJ. It's a root in some vlan's, stp mode is rapid-pvst.I wanted to see how spanning-tree is working (STP packets dump, etc.), and entered following commands on 6509: [code]
Then, I turned the "debug spanning-tree all" mode on. Now, I expect to see BPDU packets from Cisco, and other spanning tree events in logs on syslog server, or in log buffer, but I don't get anyting there. Except, there're some lines in log (they repeat very rare): [code]
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