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New Member

2900 XL VLAN Drops, Relearning Addresses

Had an odd issue that started up last few days..  Have a port on a cisco 2912 XL that keeps dropping (drops all packets) on a certain VLAN, but still passes others.  Spanning-tree for that vlan says all ports are in forwarding status.  VTP says that VLAN is still active.

This network is a little strange...  2924XL -> MotoPTP -> 2912XL -> Moto Canopy Array -> Some sites with cisco, some without all feed through canopy controller switch to single port (fa0/8) on 2912.

Getting a few of these on terminal monitoring, %RTD-1-ADDR_FLAP: FastEthernet0/8 relearning 5 addrs per min...  Sometimes this is fa0/8, fa0/10, or fa0/1.

I'm thinking the switch has just gone nuts, cause fa0/1 is direct connected to a router used for VLAN1.  fa0/8 is connected to a dumb switch on a canopy CMM as a trunk which i enabled bpdufilter on because of some spanning tree issues on VLAN1.  fa0/10 is connected to canopy PTP back to the 2924 as a trunk. VLAN69s router is off the 2924. So there aren't really any possible alternate packet paths to this switch from another switch.

I also setup SPAN and captured all packets from fa0/8 and fa0/10 (seperately) and never seen packet storms of any kind on either VLAN1 or VLAN69.

Further testing with debug, nothing on spanning tree, nothing on vtp, but on ethernet-controller addr I got some interesting results showing one mac moving from fa0/1 to fa0/8 and back to fa0/1 but it never moves, its the routers mac that is connected directly to fa0/1.  Same with some macs on the other side of the PTP link saying they are bouncing from fa0/10 to fa0/8 and back to fa0/10 which isn't possible

So any suggestions on anything else to test?  I don't have any spare VLAN capable switches at the moment so I'm kind of stuck.

Thanks in advance for any help...

Joe McDonald

Everyone's tags (3)
Cisco Employee

2900 XL VLAN Drops, Relearning Addresses


A couple of questions:

  1. Would it be possible to post an exhibit or a diagram of your network? I understand that you have excluded the possibility of loops, nevertheless, they usually are at the bottom of similar problems. I got especially alert when you indicated that you are using the BPDU Filter on a port - that would possibly make it designated forwarding even in case of loops. Perhaps the loop is not obvious but allow us to confirm that for you.
  2. About the "jumping" MAC address: is it possible that someone is stealing MAC addresses of your devices and using them for himself? That could theoretically also explain the re-learning and the logging messages.

The exhibit would help indeed - please make it reasonably detailed and complete. Thank you!

Best regards,


New Member

Re: 2900 XL VLAN Drops, Relearning Addresses

Kinda through this together this morning.  I have maps in my monitoring system, but each building / location is seperated into different maps.

The BPDU filtering was turned on because of so many STP devices sending BPDU packets on that one port due to it being a bridged wireless network on that port, and many were trying to be root at the same time (non cisco devices), some were even broadcasting invalid timers as root..  So all my Ciscos have BPDU filtering turned on where they meet the wireless network since there should be no way for an STP to come in on that port, maybe a storm but no loop..  If it is a point to point or no STP devices on a multipoint link STP is still on, and is definatly on for all locally connected ports.

The switch in question is the 2912XL in bottom portion of diagram. 

EDIT: original image link broke

Inserted low res, This Link for high res

New Member

Re: 2900 XL VLAN Drops, Relearning Addresses

Also whats the possability of a unmanaged switch in an apartment off the canopy network shown above having a bad port or malfunctioning and rebroadcasting packets back into the network?  I've had this happen once before and it is such a pain stacking process to track down a single bad switch in this network. 

I didn't design it, just trying to maintain and update.  There are consumer switches in attics laying in insulation, STP without shielded connectors all over, a severe lack of grounding or ESD discharge available, no management vlan, no broadcast domain segments, its all L2 switched from end to end though several miles of PTP and PTMP networking.

New Member

Re: 2900 XL VLAN Drops, Relearning Addresses

Some updates.. This is a post from "debug ethernet-controller addresses"

I get several of these, but this is the biggest one to note because I know for a fact this MAC is plugged into port fa0/1 without any possible loops locally...

218293: 3d17h: 00e0.8147.e558 has moved from port Fa0/1 to port Fa0/8 in vlan 1

218294: 3d17h: Add    address 00e0.8147.e558, on port Fa0/8 vlan 1

218295: 3d17h: 00e0.8147.e558 has moved from port Fa0/1 to port Fa0/8 in vlan 1

218296: 3d17h: Add    address 00e0.8147.e558, on port Fa0/1

218297: 3d17h: 00e0.8147.e558 has moved from port Fa0/8 to port Fa0/1 in vlan 1

218298: 3d17h: Add    address 00e0.8147.e558, on port Fa0/1 vlan 1

218299: 3d17h: 00e0.8147.e558 has moved from port Fa0/8 to port Fa0/1 in vlan 1

New Member

Re: 2900 XL VLAN Drops, Relearning Addresses

Hello Joseph,

Could you please provide the F0/8 interface configuration ? and from the remote switch port if possible too.

Best Regards,


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