Cisco Switching/Routing :: 2960 - Can't Reproduce STP Loop
Jun 6, 2013
I am trying to reproduce a Spanning-Tree loop in my lab that occurred on Ops, and for the life of me I cannot break it. The loop is very simple:
Cisco 2960------------FW that doesn't forward STP traffic-----------Cisco 2960
This created an STP loop. In my lab, I am substituting the FW for another Cisco 2960 with STP disabled and BPDUFilter on ingress/egress ports to stop the switch from sending BPDU's to the downstream switch to keep it in the dark, as the FW did on Ops.
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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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Feb 11, 2013
I have a 24 port 2960-S that is not communicating with a 2960-LST that it is directly connected to over fiber. The link is up on the LST but will not come up on the -S. What command should I use to bring up this link? I have tried no shut from the (Config-if)# prompt.
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Nov 24, 2012
We have a couple of cisco SGE switches connected to a single DELL, between the cisco switches we have a trunk interface. I'm not sure which setting should be configured on the switches to get it working because a loop is occuring.
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Feb 17, 2013
I have a Catalyst 3560-X PoE that suddenly stopped working. I plugged in via console and below is the output I received. It scrolls constantly and I am unable to enter ROMMON mode or stop it from scrolling. I've read of a possible problem with the IOS version but I'm unable to verify due to not being able to stop the scrolling.
Switch uptime is 4 minutes, 4 seconds
cisco WS-C3560X-24P (PowerPC405) processor (revision A0) with 262144K bytes of memory.
Processor board ID FDO1522R2AY
[Code].....
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Apr 14, 2007
We recently wanted to swap our existing WS-SUP720-base with a WS-SUP720-3B in a 6513 chassis.Had the existing configuration config saved in a txt file and replaced the supervisor. Booting went fine and we pasted in the original config. There was one failure message about unnsupported command but didnt take further notice."boot system flash sup-bootflash:" was probaly the line that the 720-3B didnt support.After wr mem and reload it went in continious loop and rebooting due to inncorrect boot device. Had to put back the old supervisor and have now the 720-3B in a 6504 chassis. Tried some commands in rommon, but are not getting any further.
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Mar 1, 2012
I Like To Intentionally Create A Layer 2 Loop in My LabI have 2960 and 3750 switches and servers with multiple NIC's and also Some PC's and Hubs. Connections and Commands And Features Which Sould Be Disabled or Enabled)
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Oct 25, 2011
I am having an issue with this device after setting the ip address and rebooting. I have tried renaming the config.text file without success. I have also tried the steps mentioned here: [URL]
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Feb 19, 2012
we recently had on our network a simple layer 2 loop problem, with big effects.Here is the situation: we have a C3750 switch, with STP activate on all ports.We don't have total control on this switchs, and for some reasons, it is possible that people connect a 2d switch on it (Cisco or non-Cisco).What happened several times is a classic case: a person interconnect 2 ports of this 2d switch, creating a loop. As the loop is created on the 2d switch only, the 1st switch detect no loop, the the uplink port keeps up.Afer this loop created, a broadcast storm occurs through the link between 1st & 2d switch .. and the storm propgates all over the LAN.I try to find some solutions to avoid that. One thing I would like to do is to find a mecanism on the first switch, which can permit to block the uplink port on the 1st switch if it sees the same MAC address as source in the 2 directions.Note that storm control, even configured to a quite low value (ie: 2Mbps) is not efficient enough to protect equipment (we have had big CPU impact on LAN equipments).
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Mar 24, 2013
I have a strange issue where spanning-tree is blocking vlans through a mesh network.Here is my set up.
2-Cisco 3560's that have two trunk ports set with do1q and a native vlan of 2. I'm allowing a client vlan (2) and a voice vlan (103) to come over the trunk. They have a native vlan of 2 so the mesh APs can get an address through DHCP. Spanning-tree loop guard is also enabled.
When connected to the mesh network, the voice vlan is being blocked by spanning-tree. I get the following erros:
000129: *Feb 28 19:24:58.289 EST: %SPANTREE-2-LOOPGUARD_BLOCK: Loop guard blocking port FastEthernet0/1 on VLAN0103.000130: *Feb 28 19:24:58.448 EST: %SPANTREE-2-LOOPGUARD_UNBLOCK: Loop guard unblocking port FastEthernet0/1 on VLAN0103.
Eventually the loop is cleared and the port is set back to a forwarding state from a blocking state. I don't want to disabled spanning-tree loopguard since I don't want to create a loop. The mesh network is supposed to act as a P2P connection between two switches. As a test I disconnected the APs from their trunk ports. I then used a cross over cable to connect the switches and no spanning tree loops occured. The mesh doesn't have STP enabled on it and should just be acting as an over-the-air connection from one switch to another.
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Jan 18, 2012
I have an Extremely Old switch that I need to connect to my network. Because it is so old I don't want it to become the Root Switch.
what is the command to change the priority. (Honestly I don't remember if it has to be a lower number 1 or a higher number ). Always get that mixed up. I've read about root guard, but I would like to prevent it manually. (It is a small network after all)It is a Cisco 2950.
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Apr 17, 2012
Do Cisco Catalyst (IOS) and specially Cisco SG300/500 support a similar feature to HP's Loop Protection or DLINK's Loopback Detection? This is an interesting feature to avoid loops caused by unmanaged switches.
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Jun 7, 2012
I have a bunch of 3750x switches that each have a 10 gig routed link back to a central 4507 (loopback = 172.30.255.255).We carved up a /24 (of course, the /24 doesn't really exist except in our address tracking spreadsheet) into a bunch of /30's for routed WAN links and /32's for loopback addresses.We started on the low end for /30 subnets (ie 172.30.255.0/30, 172.30.255.4/30, etc.).We started at the high end for the /32 loopbacks (ie 172.30.255.255/32, 172.30.255.254/32, etc.)
Well, when I try pinging 172.30.255.255 from the access layer 3750x switches, the 3750x seems to be treating it as a broadcast ping where it lists each member that responds instead of the regular !!!!! response (this makes think something is odd with the 3750x). Of course, only one member responds (the core). But even the core seems to respond with the other end of the /30 instead of the actual /32 loopback (which makes me think something is odd in the core). I could have sworn that I've setup similar topologies without problems (ie, using 10.0.0.0/32, 10.255.255.255/32, etc as loopbacks) and as long as the mask is a /32, it should work.Also, I can ping/ssh to that loopback if my laptop is on a directly connected subnet. But I can't do it from any of the 3750x switches (which are also directly connected).I've double checked for overlapping subnets, but nope. I don't see any. Routing looks fine. The actual /32 is being propagated everywhere properly.
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Jan 19, 2012
I have a 3925 Router with a 48 port switch module (part number SM-D-ES3G-48-P). I have no problem accessing the 3925 Router, but when I go into the 48 port, I get an error that reads
Error Hardware not supported by firmware. Try loading a newer software instead. System Resetting...
I know that the wrong IOS is installed on the switch, but the problem is that this is an endless loop. The switch resets then comes back to the same error. How to get the switch out of this loop so that I can load the correct IOS.
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Aug 18, 2012
The following error was seen on the switch and the Diagnostic Test Loop back failed following a new WS-6748-SFP module installation.Fabric in slot 5 detected excessive flow-control on channel 3 (Module 4, fabric connection 1)
Tried Hard reset of the module and still the error persist.
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Nov 7, 2012
I have a couple of 3560 switches running c3560-advipservicesk9-mz.122-44 and they are randomly experiencing the following:
- The switch locks up with no preceding error message in the log (I am forwarding syslog to Splunk).
- Upon reboot, the switch goes through the normal startup sequence with no error messages, then for some reason reloads the flash and starts all over again. (refer to doc)
This could happen after days or weeks. Sometimes they will go through two of these reloads on boot and be fine for awhile, and other times they will be stuck in the loop infinitely. I am using this same image with all of our 3560s, but am only having this issue with two of them.
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May 9, 2012
i have recently tried to change the catos on a Catalyst 2948G-L3 and since then i have the following message in a loop :I know that the solution would be to download a new valid image from tftp via the rommon prompt but what i dont undertand is why i cant access the rommon prompt. It justs boots with the message above in a loop
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Feb 5, 2013
We have a Cisco 3750G Core switch which has physical connections, each configured as trunks to two HP Access switches. The client who uses these access switches would like to put a link between the two, but this would create a loop.
------- Core Switch -------
| |
| |
[Code]....
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May 15, 2013
I'm trying to configure an LACP channel trunk between a CatOS C6000 and a Dell PowerConnect.
I use mode active in both sides and it works great.
But, when I connect a Catalyst 3750X to the Dell PowerConnect the channel between C6000 and PWC shutdown:
2013 May 16 09:08:20 CEST +02:00 %SPANTREE-2-CHNMISCFG: STP loop - channel 5/19-20 is disabled in vlan/instance 20
2013 May 16 09:08:20 CEST +02:00 %SPANTREE-2-CHNMISCFG2: BPDU source mac addresses: 00-04-6d-43-a4-e2, 70-ca-9b-27-46-99
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Apr 6, 2012
Here is my Lab Setup: 2691 is BGP nei to R4 router and they are not directly connected. 2691 and R4 are in same AS 6500. 2691 Config---router ospf 1 network 3.3.3.3 0.0.0.0 area 0 . Its advertising its loop back IP to OSPF domain.
router bgp 6500
no synchronization
bgp log-neighbor-changes
neighbor 6.6.6.6 remote-as 6500
neighbor 6.6.6.6 update-source Loopback3
[code]...
R4 Router
router ospf 11
log-adjacency-changes
network 6.6.6.6 0.0.0.0 area 0
[ code].....
We can see that 2691 and R4 are BGP neis and 2691 has 200.1.x.x routes in its route table. My question is why from 2691 router i am unable to ping any route learned by BGP from R4?
2691Router# ping 50.1.1.0 Type escape sequence to abort.Sending 5, 100-byte ICMP Echos to 50.1.1.0, timeout is 2 seconds:.....Success rate is 0 percent (0/5)2691Router#ping 200.1.2.0 [ code]...
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Oct 26, 2012
we are bringing up new ckt and nexus 7000's interface isn't coming up once telco gave a loop. and wee following msg when I do "sh int eth1/1".
(UDLD Tx Rx loop, port: error)
what does "(UDLD Tx Rx loop, port: error)" it mean?before loop. interface was showing as "Link not Connected".
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Sep 14, 2012
I am trying to configure a loop back interface like so: [URL], on the following device:
C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(50)SE, RELEASE SOFTWARE (fc1on port gig0/1 which is using a 1000Base-SX adapter. This is for troubleshooting purposes and it does not appear to be a feasible option. Is there another way to accomplish in the IOS?
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Oct 22, 2011
Recently we got a cisco catalyst 4500 and six 2960 access switches. I need assistance on configure spanning-tree and faster convergence on my network to avoid loop.
[code]....
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Jan 17, 2013
My management has tasked me to give them a high level overview of the different switching we can choose for our new building.
This is what I know so far.4 Closets, each closet has 450 ports,One MDF room that is will contain one UCS Chassis and a Nimble iSCSI SAN.
I am working on the spreadsheet and it looks like this (Not totally filled):
2960s3560x3750x45064510Approx cost (Each, 48PORT, POE+, 10G uplink, Dual PS, IP BASE)
6K7K8K45K75KMax Capacity192432432192384Backplane speed206464520520ProLeast ExpensiveStackable to 9Stackable to 9ProDual PSDual PSDual PSDual PSDual PSProLayer 3 opt
Layer 3 optDual SupsDual SupsConExpensiveExpensiveConNo Dual PSConLayer 2 OnlyCannot stack more than 4
For the MDF I would like to use 2 Nexus 5548's with FEX's, and the layer 3 daughter board. For the IDF's I was thinking of two 4010's.
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Nov 21, 2012
I am using a 3750 as a default gateway for multiple Vlans on a few 2960 switches. The trunk lines are configured and working and I have assigned ip addresses to each of the Vlan interfaces on the 3750. My issue is that I can only ping the ip address on the Vlan interface of the 3750 if I have a working computer plugged directly into the Vlan on the 3750. I only have 3 vlans on the 3750 that have hosts directly connected (vlans 2, 10 and 40) the other vlans ( 20 and 70) don't have any clients plugged into them on the 3750 but the hosts reside on 2 different 2960s that connect via trunk ports. How do I keep the vlan interface on the 3750 switch pingable when I don't have hosts directly connected in that vlan on the 3750? (yes, I have enabled ip routing on the 3750)
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May 21, 2013
I have a Cisco SG 300-20 as the core switch, layer 3. It is 192.168.4.6 on VLAN1 and 192.168.5.1 for VLAN2 (VOIP). All the ports are set in trunk mode. DHCP relay is setup on this switch.
The phones connected into a layer 2, Catalyst 2960-S switch. All ports are set in trunk mode. Default gateway on it is set to 192.168.5.1.
DHCP for both VLANs is provided by a Windows Server 2008 R2 server (the relay IP 192.168.4.15).
There is also an ASA 5510 in the mix which is 192.168.4.1. It has a route added to it for the 192.168.5.0 network to go to the SG 300 (192.168.5.1).
Just the two switches can ping each other on the 192.168.5.x network when I "add vlan 2" to the trunk port that is connected between the SG 300 and the 2960. The phones don't get DHCP on the 2960 switch. And I cannot ping 192.168.5.x from the ASA or anything else on the 192.168.4.x network.
After a bit of reading on intra-vlan routing for the SG 300 switch, I am thinking the SG 300 has to be the "center" of things so I need to make it 192.168.4.1 to be the gateway for both VLANs and change the ASA to 192.168.4.2 for VLAN1, etc. And I really can't do asymmetric routing with this switch.
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Nov 16, 2011
Does the Model "WS-C2960-24PC-L" Supports IP Routing or not?
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Dec 26, 2012
I'm having a strange problem where I'm not able to get through a Cisco 2960-S L2 switch when connected through vpn, while LAN-WAN traffic is working fine.The situation on site is the following:When inside the network I'm able to get to the internet without a problem. The problem is within a vpn-session. When this session is succesfully started I can ping and manage the Cisco 2960-S switch, but I can't ping or manage the Dell switch from my laptop. I can however ping the Dell from the Cisco-switch. [code]
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May 15, 2012
set up my QoS on two 2960
-------------------- ------- ------- ------------
PBX Asterisk |----|2960-1 |------|2960-2 |-----|Voip client2|
-------------------- ------- ------- ------------
-------------- |
[Code].....
This will be this configuration for all input interface right ? For the Output part I'm lost, what do I have to do ? And for the 2960-2 do I have to put the same configuration ?
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Nov 7, 2012
we hava a couple of 2960 switches and we are logging to a syslog server. Ports keep going up and down is it normal severity (error) ?
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Feb 23, 2012
We recently updated a site2site link to metro ethernet, ISP call it 100mbps LAN Extension, but to me it is just QinQ over fibre connection. Most went well, one thing (annoying to me) is we can not ping our switches on both ends anymore.
We have a 3750 in headend and another 2960 on the other end. I used to be able to ping/telnet to the management IP from one to the other. Now we can not. I think the ISP is applying some configuration on ports of their customer-premises equipments (both are Cisco switches) but agent in ISP told me no. I thought there is some configuration on Cisco switch to block "MAC discovery" but i just can not remmenber what was that and google also failed me this time.
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Apr 20, 2013
I have got two links from the same ISP, primary and secondary and connected to two different switch. The ISP have passed the trunk vlan of 30, 31 and 32 on both of the links. The ISP can't provide stp. I have got another managed 2960 series switch. How can I obtain failover on switch level.
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Feb 21, 2013
I have IP phones connected to 2960 i want to segregate traffic traffic comming from IP phones which has a COS value of 5 and want to allocate a band width of 200 MBPS for those traffic .
Can any one share sample QOS configuration for achiving this in 2960 ?
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