spanning-tree / Err-Disable finding the loop via software

Hi NG,

i need some advice/comments on finding an assumpted L2 Loop via software... instead of tracking it with shutting down the redundancy the hard way..

Setup of szenario:

3550 gi0/2 -- gi2/2 4506 -- PrtChan -- PrtChan -- 6509

Cat 4506 and Cat 6509 play HSRP whereby the 6509 is always the prio 105 of all configured vlans.

On the Cat 3550, witch is only attached to the 4506 via gi2/2, i get following messages:

Mar 30 14:16:10: %ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected on GigabitEthernet0/2. Mar 30 14:16:10: %PM-4-ERR_DISABLE: loopback error detected on Gi0/2, putting Gi0/2 in err-disable state Mar 30 14:16:11: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/2, changed state to down Mar 30 14:16:12: %LINK-3-UPDOWN: Interface GigabitEthernet0/2, changed state to down

Thats the 3550 gone to Err-Dis!

on the 4506 i get following logs:

23 08:39:53: %C4K_EBM-4-HOSTFLAPPING: Host 18:A9:05:62:4E:DA in vlan 100 is flapping between port Gi2/6 and port Po10 Mar 23 08:39:53: %STANDBY-3-DUPADDR: Duplicate address 192.168.6.3 on Vlan60, sourced by 000e.383e.483f Mar 23 08:39:54: %C4K_EBM-4-HOSTFLAPPING: Host 18:A9:05:62:4E:DA in vlan 100 is flapping between port Gi2/6 and port Po10 Mar 23 08:39:54: %C4K_EBM-4-HOSTFLAPPING: Host 00:D0:03:EA:E0:0A in vlan 110 is flapping between port Po10 and port Gi2/6 Mar 23 08:39:54: %C4K_EBM-4-HOSTFLAPPING: Host 18:A9:05:62:4E:DA in vlan 100 is flapping between port Gi2/6 and port Po10 Mar 23 08:39:54: %C4K_EBM-4-HOSTFLAPPING: Host 00:D0:03:EA:E0:0A in vlan 99 is flapping between port Gi2/6 and port Po10 Mar 23 08:39:54: %C4K_EBM-4-HOSTFLAPPING: Host 00:00:00:00:FE:01 in vlan 100 is flapping between port Po10 and port Gi2/6 Mar 23 08:39:54: %C4K_EBM-4-HOSTFLAPPING: Host 00:D0:03:EA:E0:0A in vlan 200 is flapping between port Po10 and port Gi2/6 Mar 23 08:39:54: %C4K_EBM-4-HOSTFLAPPING: Host 00:1E:0B:C3:23:78 in vlan 100 is flapping between port Po10 and port Gi2/6 Mar 23 08:39:54: %C4K_EBM-4-HOSTFLAPPING: Host 00:0E:7F:FD:58:B0 in vlan 100 is flapping between port Po10 and port Gi2/6 Mar 23 08:39:55: %C4K_EBM-4-HOSTFLAPPING: Host 00:D0:03:EA:E0:0A in vlan 99 is flapping between port Po10 and port Gi2/6 Mar 23 08:39:55: %C4K_EBM-4-HOSTFLAPPING: Host 00:90:FB:24:BA:00 in vlan 100 is flapping between port Gi2/6 and port Po10 Mar 23 08:39:55: %C4K_EBM-4-HOSTFLAPPING: Host 00:1F:29:69:9D:6E in vlan 100 is flapping between port Gi2/6 and port Po10 Mar 23 08:39:55: %C4K_EBM-4-HOSTFLAPPING: Host 00:D0:03:EA:E0:0A in vlan 100 is flapping between port Gi2/6 and port Po10 Mar 23 08:55:58: %C4K_EBM-4-HOSTFLAPPING: Host 00:50:56:83:45:A3 in vlan 100 is flapping between port Po10 and port Gi6/5 Mar 23 08:56:59: %C4K_EBM-4-HOSTFLAPPING: Host 00:50:56:83:45:A3 in vlan 100 is flapping between port Po10 and port Gi6/5

the interessting one i guess is this: Mar 23 08:39:53: %STANDBY-3-DUPADDR: Duplicate address 192.168.6.3 on Vlan60, sourced by 000e.383e.483f

when i issue the following on the 4506

asw03#sh mac-address-table | i 000e.383e.483f 12 000e.383e.483f static ip,ipx,assigned,other Switch 30 000e.383e.483f static ip,ipx,assigned,other Switch 50 000e.383e.483f static ip,ipx,assigned,other Switch

it sees its own mac addr, what a surprise! so i do guess i got some bad things happening on L2, loopin all over.

------------------------------------------------------------ as i just tried following within a complete seperate lab:

3560 fa0/2 -- fa0/1 3550 from 3550 to itself from fa0/47 to fa0/48 (looped)

on the 3550 i configured: no spanning-tree vlan 1-999 making sure it runs as if i would use some unmanaged switch, thereby creating a loop on it self.

within this LAB it was a pretty ugly szenario, since i actually thought the

3560 on fa0/2 would track it and STP would go into the Blocking state on fa0/2, but it did NOT. so the hole thing looped and flashed like an x-mas tree on fa0/2 aswell of course on the 3550.

so i am considering in order to find the loop to go and take the approach via storm-control, thereby issuing the action trap mode, in order not to shutdown my hole network.

on my Distribution Trunks/Uplinks towards the Access-Switches:

storm-control broadcast level pps 500 storm-control multicast level pps 500 storm-control action trap

i guess this should give me an idea from witch link i get alot of broadcasts..

i still can't explain why my 3550 in the real world setup went down with Err-Dis, since it is single attached to the 4506....

so if you got other idea's how to track L2 Loops without pulling out the redundancy until it stops, feel free to contact me and send me youre advice.

Thank you colin