Unanswered Question
Aug 20th, 2007

Hi NetPros,

anyone can help ?

Aug 20 17:19:44.160: %RTD-1-ADDR_FLAP: GigabitEthernet0/2 relearning 5 addrs per min

Aug 20 17:20:44.175: %RTD-1-ADDR_FLAP: GigabitEthernet0/1 relearning 6 addrs per min

switch>sh spann int gi 0/1

Interface Gi0/1 (port 40) in Spanning tree 1 is FORWARDING

Port path cost 4, Port priority 128

Designated root has priority 32768, address 0003.e35c.2580

Designated bridge has priority 32768, address 0003.e35c.2580

Designated port is 40, path cost 0

Timers: message age 0, forward delay 0, hold 0

BPDU: sent 1690479, received 1352

switch>sh spann int gi 0/2

Interface Gi0/2 (port 48) in Spanning tree 1 is FORWARDING

Port path cost 4, Port priority 128

Designated root has priority 32768, address 0003.e35c.2580

Designated bridge has priority 32768, address 0003.e35c.2580

Designated port is 48, path cost 0

Timers: message age 0, forward delay 0, hold 0

BPDU: sent 1703077, received 13968



  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (19 ratings)
ankbhasi Mon, 08/20/2007 - 02:22

Hi Kitten,

Looks like your network is hitting a STP loop. Can you brief more about topology?



b.petronio Mon, 08/20/2007 - 03:03

Could u please upload the configuration of this switch and the root bridge one.

As i remenber, u should have a different value of designated bridge priority, and one port on BLOCKING instead of 2 forwarding.


Error Message RTD-1-ADDR_FLAP [chars] relearning [dec] addrs per min

Explanation Normally, MAC addresses are learned once on a port. Occasionally, when a switched network reconfigures, due to either manual or STP reconfiguration, addresses learned on one port are relearned on a different port. However, if there is a port anywhere in the switched domain that is looped back to itself, addresses will jump back and forth between the real port and the port that is in the path to the looped back port. In this message, [chars] is the interface, and [dec] is the number of addresses being learnt.

Recommended Action Determine the real path (port) to the MAC address. Use the debug ethernet-controller addr privileged EXEC command to see the alternate path-port on which the address is being learned. Go to the switch attached to that port. Note that the show cdp neighbors command is useful in determining the next switch. Repeat this procedure until the port is found that is receiving what it is transmitting, and remove that port from the network.


Hope it helps,

Best Regards,

Bruno Petr?nio

ney25 Mon, 08/20/2007 - 05:02

Hi Bruno,

i have followed your way, enable debug ethernet-controller address.

but, nothing came up....

what can i do now , kindly enlighten me ..

your reply will be highly appreciated.



b.petronio Mon, 08/20/2007 - 05:21

Hello kitten,

We could do somethings in order to help u, but we will more precise if we got an idea of the design, and configuration, i.e.;

- is that both port, connected to te same switch?

- are them in Etherchannel mode ?

Try to describe ur design the most precise way, and give us knowledge about what is configured in ur switch's.

I'm sure, that if u show us more information, we help you better.

Best Regards,

Bruno Petr?nio

ney25 Mon, 08/20/2007 - 16:36

Hi Bruno,

nope, both port are not connected to the same switch.

no etherchannel .

but, now i have received this msg .

Aug 21 08:32:30.502: %SYS-3-LOGGER_FLUSHED: System was paused for 00:00:00 to ensure console debugging output.



b.petronio Tue, 08/21/2007 - 01:00

Hi kitten,

Did u/someone else change your stp configuration, before this happen?

Did someone perform any changes in patching, in your switchs ?

I could guess that u have a stp loop, like Ankur have pointed here, but u need to know where it is, in order to resolve it.

That 2nd message, "%SYS-3-LOGGER_FLUSHED", is saying that ...

"Debugging or informational messages are being generated faster than they can be displayed on the console.To guarantee that they can be seen, the rest of the system is paused until the console output catches up."

Assuming that u only have cisco switchs, in ur network, and all have the cdp active, and if u have a network design showing connections between them, u need to check up where is that loop, using "show cdp neighboors".

I would start, right on that switch and check all the connections.

If u could give us the network design topology, we would appreciate.

Hope it helps,

Best Regards,

Bruno Petr?nio

ney25 Tue, 08/21/2007 - 04:26

Hi Bruno,

attached with the network diagram and kindly advice.

so, when i show the spanning-tree on the switch ( i saw the gi0/1 and gi0/2 became FORWARD.

your reply will be highly appreciated.

thanks a lot. and hope to hear from you.



b.petronio Tue, 08/21/2007 - 05:47

Hi there,

Regarding your design, i surely believe that if the users in that switch ( is experiencing problems, than u could shutdown Gi0/5 OR Gi0/6 in, in order to avoid the loop, but then i think it's harder to search the problem.

Nevertheless, oyu could perform a "show cdp neighboors" in each switch, and check for differences with the design u gave us.

Do u have any spanning tree priorities configured in any equipment ?

Perform a "show run | inc spanning" and past it here refering on which equipment its.

Hope it helps,

Best Regards,

Bruno Petr?nio

ney25 Tue, 08/21/2007 - 05:54

Hi Bruno,

yes, i have check all switch with using " show cdp nei " . as i can't see any loop back port in the same switch. some more i did shut down the int gi 0/6 but the switch is down imeediately.

but, i noticed something.. all of my switches which configured spanning-tree mode pvst but only this has not spanning-tree mode pvst. well, this is 3524XL model and version 12.0(5.2)XU. and when i try to configure spanning-tree mode to this switch. that's no such spanning-tree mode function for me.

would that be the IOS version was outdated ?

b.petronio Wed, 08/22/2007 - 01:03

Hi there,

I'm a bit surprised that u lost connection after shutting down G0/6. Do u wait for some seconds?

It should converged...

1st of all, and before we make anymore changes, i would ask u, if this was happening after some changes ? or it's happening since it was installed ?

I arrange a 3524 with the same ios version and done a "debug ethernet-controller", and "term mon", and i saw a debug output... like this :


Aug 22 08:44:29.185: Add address 0030.0556.d218, on port Gi0/2 vlan 1

Aug 22 08:44:29.300: Add address 0010.839f.2864, on port Gi0/1 vlan 1

Aug 22 08:44:29.539: Delete address 0016.3565.1dfb, on port Gi0/1 vlan 1


This should help u find where is the relearning loop.

Nevertheless, and regarding PVST (Per-Vlan Spanning Tree), i think that its not the issue, if u only use Vlan 1. (its the only vlan in use ? )

I my self, have 2 switchs in my network, similar with ur design, 1 3524 (no pvst)+ 1 2950 (pvst) Vlan1 only, but i have priority configured in 2 redundant core switchs.

Please paste your configuration of,,, and please.

I really suspect on that cost for both interfaces (4).

Maybe some switch expert could comment this issues and give us a light on this.

Best Regards,

Bruno Petr?nio

avmabe Wed, 08/22/2007 - 05:57

Looking at the diagram and reading these posts... Just make SURE the switch in the middle is configured as the ROOT BRIDGE for STP. My guess is that it is not.

Once you verify you have forced that center switch to be the ROOT, then you can troubleshoot any issues that may be evident.

ney25 Wed, 08/22/2007 - 07:13

Hi ,

mind to tell me how to configure the middle switch as the Root Bridge for STP ?

basically i have only 1 Vlan in the entire network. (Vlan 1).

your reply will be highly appreciated.



b.petronio Mon, 08/27/2007 - 01:51

Hi there,

The config u gave us, don't give me any clue.

Do u have any news ?

Best Regards,


ney25 Mon, 08/27/2007 - 05:07

Hi Petronio

no, that what i have only :(

that's why i am very headache about how to find the loop from this network ?

jorgenolla Mon, 08/27/2007 - 06:02


It will help if you post the outcome of STP for each switch, this way we can see the STP topology; who is acting as the root bridge in each switch, and what states are the port on.

Best Regards

ney25 Mon, 08/27/2007 - 17:17

Hi Jorgenolla,

yes, that's what i wanted to do so.

p/s : switch (Gi0/6) and (Gi0/2) Port have been shut down.


avmabe Mon, 08/27/2007 - 17:26

You never set the root.

The switch is currently the root bridge and that is not good.

Also, why not just plug all the devices straight into the 3750 and not the 51.211 box?

If I inherited this network, I'd plug all switches straight into the 3750 and make the 3759 the root bridge for the network.

ney25 Mon, 08/27/2007 - 17:48

Hi avmabe,

yes, i agreed with you but i can not change this design due to some " shit " reason.

so, what i can do is just find the root cause and cure the network now.

so, any suggestion and guidance ?

your reply will be highly appreciated.

b.petronio Tue, 08/28/2007 - 01:12

Hi there,

I'm totaly agree with avmabe, unless u have physical contrains.

I cacn give u know a brief explanation, about why is is assuming the root.

The Lower mac-address in each switch vlan 1, is the (0003.e35c.2580).

And in each switch, they all have diferent cost's to the root, cause they have different paths.


GigabitEthernet = Cost 4

210 to 216 = 4+4+4+4 = 16

211 to 216 = 4+4+4 = 12

212 to 216 = 4+4+4+4 = 16

213 to 216 = 4+4+4+4 = 16

214 to 216 = 4+4 = 8

215 to 216 = 4 = 4

So all the output u gave us, point to the root bridge on

If u could try to do what avmabe said so.

Best Regards,

Bruno Petr?nio

jorgenolla Mon, 08/27/2007 - 18:20

I needed to see the Topology as in Production mode not with the ports shut down. If you have shut down does ports, which the file you posted confirms; I will not be able to tell the actual working topology, and the problems on it.

If you can please post the STP output with Gi 0/6 on 51.211, and Gi 0/2 on 51.216 on.

Best Regards

ney25 Mon, 08/27/2007 - 18:40

Hi Jorgenolla,

sure, as requested.



interface GigabitEthernet0/6

switchport mode dynamic desirable





interface GigabitEthernet0/2



p/s : actually this network very messy which no standard (dot1q) coz, some of them using (isl). does this will affect to the entire network as well ?


jorgenolla Mon, 08/27/2007 - 20:12

Once the interfaces are up, STP will run STA, then the network will converge, after which you need to upload the output of all switches as you did before.

Best Regards

ney25 Mon, 08/27/2007 - 20:26

Hi Jorgenolla,

so, beside redesign the network, any idea how to cure this network ? coz, i believe some loop still in this network .

jorgenolla Tue, 08/28/2007 - 04:16

I really need to see the STP topology in all switches, with all interfaces on no shut, to be able to give you any help.

ney25 Tue, 08/28/2007 - 05:27

Hi Jorgenolla,

attached with STP config for all switch.

but, i noticed the switch 51.215 , that's the root at Gi0/2, some more when i show interface trunk. i can't see the Gi0/2 as trunk , but it is connected to switch 51.216

switch#sh spann


Spanning tree enabled protocol ieee

Root ID Priority 32768

Address 0003.e35c.2580

Cost 4

Port 50 (GigabitEthernet0/2)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 000d.29b5.1640

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/3 Desg FWD 19 128.3 P2p

Fa0/9 Desg FWD 19 128.9 P2p

Fa0/10 Desg FWD 19 128.10 P2p

Fa0/11 Desg FWD 19 128.11 P2p

Fa0/12 Desg FWD 19 128.12 P2p

Fa0/13 Desg FWD 19 128.13 P2p

Fa0/14 Desg FWD 19 128.14 P2p

Fa0/16 Desg FWD 19 128.16 P2p

Fa0/17 Desg FWD 19 128.17 P2p

Fa0/19 Desg FWD 19 128.19 P2p

Fa0/27 Desg FWD 19 128.27 Shr

Fa0/40 Desg FWD 19 128.40 P2p

Gi0/1 Desg FWD 4 128.49 P2p

Gi0/2 Root FWD 4 128.50 P2p

switch#sh int trunk

Port Mode Encapsulation Status Native vlan

Gi0/1 desirable 802.1q trunking 1

Port Vlans allowed on trunk

Gi0/1 1-4094

Port Vlans allowed and active in management domain

Gi0/1 1

Port Vlans in spanning tree forwarding state and not pruned




Gi0/1 connected trunk a-full a-1000 1000BaseSX

Gi0/2 connected 1 a-full a-1000 1000BaseSX



jorgenolla Tue, 08/28/2007 - 07:03

3524XL models do not support DTP (Dynamic Trunking Protocol), you must trunk all links to be trunk manually. This is something a lot of your switches are missing, according to the output you've posted!

I have attached a view of what ports should be Root Ports, and what ports should be in the Blocking state, in accordance with your lan diagram, and given no manual priority or cost changes have been made.

You've sent on your last post the state of the trunk ports, but you didn't send the

#show spanning-tree

command output for all switches. I need to see that in order to be able to tell you if spanning tree is working correctly.

Also ensure you have entered a lower priority on 51.216, by using the command:

#spanning-tree vlan 1 priority 4096

on the global config mode. this will ensure no changes on the Root Bridge for STP

Best Regards

ney25 Tue, 08/28/2007 - 07:12

Hi Jorgenolla,

attached with show spanning-tree for all switches, kindly have a look.

your reply will be highly appreciated.

jorgenolla Tue, 08/28/2007 - 09:15

Ok I believe the problem relies on your Trunk Ports and not on STP. The only STP discrepancy which really should not affect your topology; is found on 51.214.

Gi 0/1 should have been chosen as the Root port, and Gi 0/2 should have been blocked.

Reason being, they both have a total path cost of 8, but the Port id is lower on Gi 0/1 being 128.49, and 128.50 on Gi 0/2. But still since once is blocked, STP should not have any loops.

If you are using 2900XL/3500XL series switches, they do not support DTP, and I believe this is where the problem lies, and not on STP.

One of the text files you had sent earlier, confirmed that the not all port that are on p2p between switches, were actually trunked.

The following switches must be configured manually to switchport mode trunk on it's p2p interfaces with other switches:








So basically all of your switches, at this moment are running in switchport access mode, and not in Trunk mode.

The only link that is actually Trunked in your topology is the link:

51.216 Gi 0/2 To 51.211 Gi 0/6

After you have set all the rest of the links to switchporrt mode trunk, you should have no further problems with the address flapping that you had before.

Here is an article, that has some information on this problem:


Please let me know how it goes after you enable trunking on those ports.

Best Regards

ney25 Tue, 08/28/2007 - 16:56

Hi bro,

so, you mean all uplink port configure as Trunk (dot1q) the problem will be resolved ?

because, i noticed some pple connect the one of the switch port (i.e fa 0/23) to some hub (unmanaged hub), so could this cause the loop as well ? because, currently all ports have no any configuration like switchport mode access, so do you think i should put all ports as switchport mode access ?


jorgenolla Tue, 08/28/2007 - 18:24

When you a link is from a switch to a switch that link should be configured to switchport mode trunk. All ports are configure as switchport mode access by default.

A hub is layer one device; which is totally different thing; and not part of the topology diagram you posted.

ney25 Tue, 08/28/2007 - 19:02

Hi Jorgenolla,

yes, that's no in my diagram . because, i just noticed when i trace all switch ports , i noticed some port which consist 3 MAC addresses .. so, when i called them to verify .. they told me that's some limitation for the switch usage that's why they cascade for hub for some installation work for desktop PC.

so, my point is even they cascade a Hub in between , does this will cause the loop ?

should i configure this port to "switchport mode access" also ?


avmabe Tue, 08/28/2007 - 19:07


you should give jorgenolla some points for all the help you are receiving.

Do you have smartnet on any of these switches?

If so, call the TAC.

If not, set the center switch to ROOT BRIDGE that was recommended days ago.


This Discussion