Spanning Tree: %SW_MATM-4-MACFLAP_NOTIF

Hello All,

I'm seeing the MACFLAP_NOTIF errors when I change my native vlan to 46 after
I trunk two ports together. If I put these back to vlan 1 the errors stop.
I believe I have a spanning tree loop as both switch 1 & 2 are the roots
and ports 13 &15 on both switches are forwarding.

sw1 f0/13----sw2 f0/13
sw1 f0/15----sw2 f0/15

I have two questions:

 a) Why does this happen when I change the native vlan, what is it that
confuses spanning tree?
b) If I see this error on the CCIE lab and I have full connectivity should I
try and troubleshoot or just move on to finish the lab? Will I lose points
for this error if I have full connectivity?

Thanks in advance

----Details Below

12:02:55: %SW_MATM-4-MACFLAP_NOTIF: Host 0010.2930.b701 in vlan 1 is
flapping between port Fa0/13 and port Fa0/15
12:02:55: %SW_MATM-4-MACFLAP_NOTIF: Host 0007.eba9.df81 in vlan 1 is
flapping between port Fa0/13 and port Fa0/15
12:02:55: %SW_MATM-4-MACFLAP_NOTIF: Host 0050.0f05.6a21 in vlan 1 is
flapping between port Fa0/13 and port Fa0/15
12:02:55: %SW_MATM-4-MACFLAP_NOTIF: Host 000f.f780.eed0 in vlan 1 is
flapping between port Fa0/15 and port Fa0/13

Rack1SW1(config)#do sh int trunk
Port Mode Encapsulation Status Native vlan
Fa0/13 on 802.1q trunking 46
Fa0/15 on 802.1q trunking 46

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

Rack1SW2(config-if-range)# do sh span det
 VLAN0001 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, sysid 1, address 0014.6aa3.f880
  Configured hello time 2, max age 20, forward delay 15
  We are the root of the spanning tree
  Topology change flag not set, detected flag not set
  Number of topology changes 17 last change occurred 00:47:00 ago
          from FastEthernet0/2
  Times: hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0, aging 300
 Port 13 (FastEthernet0/13) of VLAN0001 is designated forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.13.
   Designated root has priority 32769, address 0014.6aa3.f880
   Designated bridge has priority 32769, address 0014.6aa3.f880
   Designated port id is 128.13, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 8162, received 71
 Port 15 (FastEthernet0/15) of VLAN0001 is designated forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.15.
   Designated root has priority 32769, address 0014.6aa3.f880
   Designated bridge has priority 32769, address 0014.6aa3.f880
   Designated port id is 128.15, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 8166, received 69

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

Rack1SW1(config)#do sh span det
 VLAN0001 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, sysid 1, address 0014.f20d.7780
  Configured hello time 2, max age 20, forward delay 15
  We are the root of the spanning tree
  Topology change flag not set, detected flag not set
  Number of topology changes 24 last change occurred 00:47:10 ago
          from FastEthernet0/3
  Times: hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 1, topology change 0, notification 0, aging 300
 Port 13 (FastEthernet0/13) of VLAN0001 is designated forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.13.
   Designated root has priority 32769, address 0014.f20d.7780
   Designated bridge has priority 32769, address 0014.f20d.7780
   Designated port id is 128.13, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type is point-to-point by default
   BPDU: sent 7993, received 90
 Port 15 (FastEthernet0/15) of VLAN0001 is designated forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.15.
   Designated root has priority 32769, address 0014.f20d.7780
   Designated bridge has priority 32769, address 0014.f20d.7780
   Designated port id is 128.15, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 2
   Link type is point-to-point by default
   BPDU: sent 7992, received 89

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Received on Mon Apr 27 2009 - 22:37:12 ART