Cisco Switching/Routing :: STP Stops Loops But R-PVST Goes Flapping 2960
Feb 22, 2012
Stange problem which I encountered today, I have a Cisco 2960 which is connected to a netgear. The switch started showing itself in CDP and was running STP. I checked the cables physically today and noted 3 uplinks to the netgear, all port on the Cisco active and forwarding and green lights.
The Cisco was running STP, I changed it to R-PVST and the lights on the Cisco went crazy and I got the message port flapping on the switch but the switch did not block any ports (all ports on same vlan).
There after I changed it back to stp and the switch blocked the other up links apart from one.
Sure R-PVST is far superior than STP?
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Dec 15, 2011
As a part of a major network cleanup/standardization project I have been working on for several weeks, I am now looking at spanning-tree and trying to get my company into line with Cisco Best Practice. I currently have 3 switches in the data center that are spanning-tree root for different vlans. Before I changing vlan priorities in spanning-tree, I feel that I should change from PVST that everything is on now to Rapid-PVST. To minimize the momentary network disruptions from making the change, should I do the edge switches first and do the switches in the data center at the last ?
Related to this process is something that I want to do probably after the PVST to Rapid-PVST change. I am going to manually set the vlan priorities for each vlan on the main core switch. Assuming I set the vlan priority for each vlan on my main core switch (6509) to 4096, should I set the switch I want to be the backup to 8192 for each vlan and then set the edge switches to something like 12288 to keep them from getting up in the spanning-tree hierarchy and for general principle to leave nothing to chance ?
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Feb 4, 2013
I have a 2960 switch and every then and now the ports are flapping, while i was on console i saw ports going down and coming up...when the ping to machine ip addresses timed out the port status on switch was still up...no errors collisions seen on sw port. Below is sh int when the port was flapping
[code]...
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Jul 23, 2012
we have cisco 2960 switch which is connected to a cisco 2811 router. flapping issue between these two devices??
The following actions i have taken, but no result.. I have changed cables. have set speed to 100 and duplex full on both the interfaces but the interfaces are showing up up still not getting connectivity. same i have to auto on both sides still no result what configurations should i set to resolve this issue...?
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Nov 15, 2011
i'm trying to type the command (config)#spanning-tree mode rapid-pvst on my Cisco 2950, but (config)#spanning-tree mode ? only shows me one option - pvst. I've checked the Cisco support page which suggests my version of IOS should support rapid-pvst.
Switch_1#sh ver
Cisco Internetwork Operating System Software
IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(13)EA1, RELEASE SOFTWARE (fc1)
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Jun 13, 2013
Is it possible to configure MST on ASR and have rapid-pvst on 7600? can they interoperate? ASR sees no BPDUs and both are root bridges.
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Dec 14, 2011
Any opinion on what could cause loops on nexus 5000 ports that are connected to esx hosts ?
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Jan 20, 2012
I have a network where if an end user attaches an hub to the network, or rather one of those cheap unmanaged 8-port mini-switches and then plugs the two ends of the same cable into two ports of that mini-switch, all the network goes down. Loops are generated and many uplinks are shut down in err-disable state due to the loopback reason.
I know I could discourage the use of those mini-switches using port security. I even have NAC (cisco) deployed on the network, but there are cases where that mini-switches are allowed by the managment.In those cases, is not possible to exactly know wich hosts (mac addresses), and even how many of them will attach the network concurrently.As I know, they could even chain many mini-switch one to another. Of course, when even a single mini-switch is allowed on the network, it raises as a security hole.
Is there a way to allow the use of those devices without the risk of network outages? Some STP protection method? The best would be to have the Cisco access switch to get aware of the loop on its affected switchport (where the mini-switch is attached), immediately shutting down that port (to avoid loops on the network) and maybe sending an SNMP trap or a syslog message.
We are using Cisco Catalyst 2950 and 2960 for our access layer.
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Mar 14, 2013
I have an alcatel 6850 switch connected to a 3750. Two connections (cables) are used between the switches. The two connections from the alcatel are in different vlans 10 and 60 , but the cisco ones are in the same vlan ie 1 (I know not best practice but keep with it ). The cisco cables are connected into port 1 and 4. Port 1 is forwarding and 4 is blocking. The 3750 is configured with basic default pvst configuration.The alcatel is the root bridge. As can be realised traffic from alcatel on vlan 10 cannot pass traffic to the 3750, This was established by the spt seeing the same mac from the root bridge therefore blocking port 4.To stop this from blocking in this scenario I was going to use bpdufilter.
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Mar 23, 2013
I can not enable to rapid- protocol in catalyst 6513, does not support for it, only support pvst.
Someone how can i enable to rpvst? You know if is necessary to upgrade IOS, it has
s72033_rp-ENTSERVICESK9_WAN-M - 12.2(18)SXF9 IOS. The cisco software Advisor could not localized the features fot this IOS.
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Jan 18, 2012
We have two L3 3750 switches running HSRP and routing for various Vlans on our corporate network. Rapid PVST is running across our entire WAN. We are introducing a third party solution for remote communications over MPLS. When interconnecting this equipment to our core network, we have experienced less than desirable failover times of 32 seconds and recovery times of 60 seconds. The vendors engineers are telling is that the interoperability between IEEE spanning tree and Rapid PVST is the culprit.
They are suggesting two scenarios - either converting our corporate network to MST (which I prefer not to do but provides us the fastest fail/recovery times) or adjust the timers on our Rapid PVST forwarding timer to 4 seconds. What would the implications be to change these timers on our network, and if I choose to do this, do I only do it at the core (on the two devices that would become root bridge)? I have been doing some reading that says to not mess with the timers, but nowhere do I see reasons why.
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May 22, 2013
We have an environment where users create a lot of bridge loops. We have tried to send E-mails about it and educate the users but it is almost a lost cause at this point. The loops are created when users don’t pay attention and they plug a patch cable coming off of an access port up to ANOTHER access port by mistake.
All of our access ports are from 3750 stacked switches. The way we tried to deal with this in the beginning was with BPDUGuard and ERRDiable (BPDUGuard) auto recovery. We turned BPDUGuard on globally and left BPDUGuard auto recovery at the default value (I believe it was 30 seconds). so a loop would be detected and after 30 seconds, the switch would try to enable the port and if the loop still existed, close the port for 30 more seconds. Then we started having problems with printers getting "fried". Their NICs would die out and the control board would need to be replaced. After a lot of troubleshooting and testing, it was determined that allowing the ports to come out of ERRDisabled state would flood the network and the packets would generate in the millions per second range and fry the NIC of these printer.
The fix for this and saving the printers was terrible. We removed ERRDisable auto recovery and just let the ports that are looped stay in an ERRRDisabled state. We wait for the user to figure out the loop and try to use the port and then put in a work order. Then we physically visit the site and verify the port was shut (ERRDisabled) from a loop and we bounce the port (shut/no shut) and everything is resolved. I did lab tests with a switch looped and a printer on the switch and watched it fry. We have had no printers fry after we removed the auto recovery protocol at every location. Only the locations where loops existed and auto recovery protocol running were printers going bad. What I found during my lab tests was that each time the port was auto-recovered (yes, for that millisecond while it checks if a loop still exists), more packets were re-generated and eventually enough was re-broadcastthat printers would go down. We never had a problem with computer NICs. I guess the cheaper printer NICs couldn’t handle the broadcast storms created by this. I tried playing with the auto recovery timers and even the highest setting would eventually re-create these storms.
So my question is what best practices are others using? Should we get rid of BPDUGuard and just try to let spanning-tree handle these bridge loops? Is there something else I can try? I’m not CCNA by any means, just trying to do what I can in my environment. Manually visiting sites when loops occur is becoming more and more my job, though and I have plenty of other things to be doing.
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Apr 1, 2013
I have two locations DC and Corp connected to each other via Point to Point Circuit. I have forced the two core switches setup as GLBP pair to be primary and secondary for certain VLAN's including VLAN1.I have a switch in our Corporate office 3750 which is where the point to point circuit terminates. VLAN1 SVI is manually shut on that switch. Also the priority on VLAN1 is increased manually like this, "spanning-tree vlan 1 priority 28672".
Now the issue is that the Primarey Root Bridge in the DC is the root bridge for VLAN 1. But this other switch 3750 in our corporate office also is a root bridge for VLAN1. [code]
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Nov 14, 2011
3750 switch connects to Blade-switch_1 and Blade-switch_2 Spanning-tree mode is configured as rapid-pvst on 3750 switch, do I need to configure rapid-pvst on both blade-switches or keep the default pvst config.3750 is running VTP domain HQ and transparent mode Both Blade_switches are running VTP domain CLI and transparent mode To configure Etherchannel between 3750 and blade-switch_1 do I need to have all devices in same vtp domain?
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Sep 22, 2011
I recently upgraded my network to have two 3750x core, one interface on the cisco is connecting to a Netgear switch via a fiber converter. I am keep getting the vlan flapping error message in my log as below.
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Jul 9, 2012
i have 2 cisco 7604 distrubution routers .Both routers are running 310 hsrp groups.
Sundenly there is hsrp flapping which causes high CPU.
What is the limitation of HSRP group on cisco 7604 router .Below is the show ver from the router
----------------- show version ------------------
Cisco IOS Software, c7600rsp72043_rp Software (c7600rsp72043_rp-ADVIPSERVICES-M), Version 12.2(33)SRC2, RELEASE SOFTWARE (fc2)
[Code]......
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Apr 14, 2013
i have a question, i have in the logging of my switches a mac falpping problem. i have a log notification : Apr 12 19:33:13: %SW_MATM-4-MACFLAP_NOTIF: Host xxxx.f065.520c in vlan 25 is flapping between port Gi0/1 and port Fa0/35. When i look up what is connected to interface FA0/35 it is a accespoint " AIR-AP1242G-A-K9" Cisco IOS Software, C1240 Software (C1240-K9W7-M), Version 12.4(21a)JA1, RELEASE SOFTWARE (fc1)
How this is making the mac flapping ?
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Jun 27, 2012
We have been receiving these notifications on one of our core.
Jun 28 12:54:01: %MAC_MOVE-SP-4-NOTIF: Host b407.f9c3.3c51 in vlan 56 is flapping between port Po5 and port Te7/2
Jun 28 12:54:01: %MAC_MOVE-SP-4-NOTIF: Host 145a.05c8.0ed3 in vlan 802 is flapping between port Te7/2 and port Po5
Jun 28 12:54:01: %MAC_MOVE-SP-4-NOTIF: Host 9463.d129.546a in vlan 56 is flapping between port Gi2/9 and port Po5
Jun 28 12:54:01: %MAC_MOVE-SP-4-NOTIF: Host 3c43.8ef3.7448 in vlan 56 is flapping between port Gi2/9 and port Po5
Jun 28 12:54:01: %MAC_MOVE-SP-4-NOTIF: Host 000e.35eb.25ae in vlan 66 is flapping between port Po5 and port Te7/2
PO5 goes to our primary wireless controller. Gi2/9 goes to a Cisco 4500 switch that also has a PO5 on it for a failover lan controller and TE7/2 is another core switch.
These mac-address all seem to point to PO 5 which is the port channel assigned to Wireless Controller interfaces.
How do I determine if this is a spanning-tree loop? No ports are err-disabled.
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Jun 4, 2012
We have some legacy Cisco 6513 switches with the backbone (16-port GBIC blade) MTU set to 1500. It has a WS-X6148A-GE-TX blade as well, MTU set to 9K.
Now we have a customer sending MTU of 1546, their copper interface terminating on WS-6148A keeps flapping. Does the flapping have something to do with the backbone set to 1500? We cant set the backbone to 9K at this moment since it may be intrusive (reuire a reboot).
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Feb 27, 2012
We have two switches WS-C2960S-24TS-L running in stack with running IOS c2960s-universalk9-mz.122-55.SE3.We have connected two checkpoint devices on Gi1/0/24 and Gi2/0/24 with a simple configuration:
interface range GigabitEthernet1/0/24, gi2/0/24
switchport access vlan x
switchport mode access
spanning-tree portfast
On the devices log we get the following message:
%SW_MATM-4-MACFLAP_NOTIF: Host 0000.0000.fe21 in vlan x is flapping between port Gi2/0/24 and port Gi1/0/24
The mac-address 0000.0000.fe21 is not found on any checkpoint interface. "Show mac-address int gi1/0/24 or gi2/0/24" does not show the correct mac-address of the checkpoint interface connected to the port, but instead shows 0000.0000.fe21.Is there a bug in the IOS, something wrong with the switch config or does it have something to do with the checkpoint config?
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Nov 15, 2011
This is the message that I am getting from my 1941w router. I have a isakmp tunnel built with a GRE tunnel going through it.
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Mar 28, 2013
Lately I have been noticing mac flap messages on some of our access layer 3750G switches. Just a little background on how this is setup.
These 3750G switches are stacked and uplinked to a distribution layer 3750E stack (2 switches) via cross stacked etherchannel. (Usually 4 links) The access layer switches are stricly layer 2 where the distribution layer 3750E is routing the VLANs at the access layer to to the core 6500 switches.
I have just about ruled out physical loops on these stacks for the reason that the Macs are flapping. I am seeing this on two different stacks now each having 3 switches in the stack at the access layer. The cross stack etherchannel is spanned across the first two switches at the access layer and connected to both switches at the distribution layer. I have checked the etherchannel status and all ports appear to be part of the etherchannel and they appear fine.
The mac addressses that are flapping are just plain old desktop machines that plug directly into the access layer. I usually see this when the mac is learned on a port such as when a machine is plugged into the network or reboots.
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Dec 6, 2012
Two days back my entire network was behaving in unusual ways.When is connect to core switc(4506e) through console. [code]
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Mar 5, 2013
Would like to ask whats the correct snmp config so that it will send to our snmp server when a mac flapping occurs on a cisco switch specifically 4507 switches.
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Aug 27, 2012
I work for a Wireless ISP and the device impacted is the back haul radio into the site. I have swapped from a 2950T to a 3550. Replaced the radio, PoE, patch lead. We have re ran the cable up the tower using shielded outdoor cable with a drain wire which has been earthed to an earthing block in the cabinet. We have other devices on the tower not experiencing the issue. We suspect cable interference however am now at a loss to diagnose further.
[Code]....
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Mar 10, 2012
We have a pair Cisco 6509 switch in which 2 * 48 Port 1G line cards and 1 * 16 Port 10G line Card, FWSM and Sup 720 are installed.We have Cisco UCS and HP Blade servers.Cisco UCS servers are connected to Cisco 6509 switch using Fabric Interconnect, and HP Servers are directly connected to core switches.Recently the team made many changes in the network. Upgraded the IOS in Cisco 6509 switch, Configured Port profiling , MAC Pinning , HBA Cards to UCS / Nexus 1000V Infrastructure. After this change they lost the connectivity to UCS and HP Serers. Every tower is checking at their end.
The Network Team has reverted back the core switch with old IOS , but still the problem persisit.I could only see the following error log in the core switch. There are two port-channels one between core 1 and core 2. The other is between core switch and FWSM module. [code]
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Oct 2, 2012
I have Cisco 1811 and Cisco 2960 interconnect with each other by TRUNK link. As time pass i recieving below log on cisco 1811 router.
DTP-5-NONTRUNKPORTON: Port Fa8 has become non-trunk
LINEPROTO-5-UPDOWN: Line protocol on Interface FastEtherne t8, changed state to down
LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan100, changed state to down
LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan200, changed state to down
LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan300, changed state to down
LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan400, changed state to down
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Sep 15, 2012
I recently upgraded my network to have two 3750x core, one interface on the Cisco is connecting to a Net gear switch via a fiber converter. I am keep getting the vlan flapping error message in my log as below.
003396: Sep 17 01:46:16.328: %SW_MATM-4-MACFLAP_NOTIF: Host 5c0e.8ba7.0a5c in vlan 2 is flapping between port Gi2/0/15 and port Gi2/0/13
003397: Sep 17 01:46:19.843: %SW_MATM-4-MACFLAP_NOTIF: Host 5c0e.8ba7.0a5c in vlan 2 is flapping between port Gi2/0/15 and port Gi2/0/13
003400: Sep 17 01:49:58.769: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet2/0/17, changed state to down
[Code] .....
After my research i think this is a looping issue but I'm unsure how to address it.
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Jun 2, 2013
i just configured a C6K VSS with Sup2T, 15.1SY IOS software and a WS6724-SFP module with the follwing cos config:
auto qos default
table-map cos-discard-class-map
map from 0 to 0
map from 1 to 8
map from 2 to 16
[code]....
After applying the service policy to one interfac of the WS6724-SFP module the policy is deployed to all interfaces of the module. So far it should be ok but after a short time all interface of the module begin to go down an up and down and up ... flapping.
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Aug 27, 2012
I am receiving the following error message on a Cisco 3750 switch stack. Need troubleshooting this error message.
00:03:13: %SW_MATM-4-MACFLAP_NOTIF: Host 00d0.7400.2730 in vlan 600 is flapping between port Gi2/0/3 and port Gi2/0/2
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Sep 11, 2012
I have two Core 6509E SUP2T configued as VSS and has two 48 ports fiber blades. I have two 3750s, I have two gig on each 3750 port-channle to po1 and connected to both the core, one link to each core.Now, I was asked ot add two more links on each 3750 switch to make it a total of 4 gigs on each 3750s (all 4 gig ports/uplinks will be in used an dtwo links to core one an dtwo links to core 2).when i added two additional links on 3750s and bundled them to po1, I created another port channel on core and bundeled the additional two gigs on each core to accomodate for the two additional links (ports on core switches are not consequtives).
adding these two additional ports makes the 3750 switches flap between managemnet vlan and po1.now, i am not sure if I must have added the two additional links on the core to teh current port-channel or core!? I have created another port-channel on core to accomodate for this currently!?
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Mar 11, 2012
I have an issue with a Cisco 3750 switch stack which is connected to two seperate upstream Cisco 3750's which are administered by an ISP. The ISP is experiencing MAC address flapping from one of my VLAN SVI's i am using to route traffic upstream
[code]...
As you can see I utilise a VLAN SVI to route traffic to the upstream 1.1.1.2 (illustration only) IP. As per the diagram of the topology attached, the ISP is receiving a MAC address flapping error confirming the SVI MAC address from my switch stack is being learnt on the trunk port connecting switch 1 and switch 2, and also the port (Gi1/0/48) directly connected to my switch stack. As these are all Layer 2 links essentially being passed upstream and then connected between the two ISP switches, we have a 3 way triangular loop formed.
If I was to remove the port channel configuration from the two ports associated with the VLAN SVI, am i right in suggesting this would still form a layer 2 loop? The two ports would still be a member of the SVI VLAN, and it is the VLAN MAC address which is being learnt by the two ISP switches on different interfaces.
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Feb 7, 2012
I have an existing stack of 4 x 2960-S switches connected by stack cables.I would like to add another 2960-S switch to the stack but am unable to as the 2960-S will only allow 4 x 2960-S switches per stack.how I would add the 5th 2960-S switch to the existing stack of 4 x 2960-S switches.
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