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spanning tree loop

Hi All,

i have 3512 switch which is connected as per

following diag. this network is service provider

network running MPLS

1. A-6509-port-3/17 priority is - connected to fa0/12 to

A-3512 A-6509 is acting as L2 and 1 gig port this

A-6509 is connected to another B-6509 which is acting

as L3

2. A-3512 fa0/11 is connected to another switch

that is A-Extreme box . This extreme box 1 port is

connected to A-6509. and one more port of this extreme

is another B-Extreme box and again that B-Extreme box

1 port is connected to A-6509, which is acting as L2.

we have formed the ring between all the switches.

my problem is that in 3512 switches port number fa0/11

and fa0/12 coming as a fowarding port. that';s why it

is creating STP loop. and getting aftected on another


if the A-3512 both ports that is Fa0/11 and Fa0/12

is up then phasing porblem. right now i hv disconected

fa0/11 so not otherswith r getting affected.

and i am getting following log mesgs

%RTD-1-ADDR_FLAP: FastEthernet0/1 relearning 42 addrs

per min

i hv done the debug ethernet-controller adresses and

found that port where MAC address is moving

consistently between different ports. but still both

ports r in forwarding

can any body give me solution. that why both ports r in forwarding mode.

  • Other Network Infrastructure Subjects

Re: spanning tree loop

There is a bug in a very limited manufacturing run of 3500's such as the 3512's that have a bad spanning-tree defect. Check out this page:

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