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Switch Flapping

Posted on 2008-10-28
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Last Modified: 2009-01-10
Hey all i have 2 switches which are both onnected to a router, and the router is configured with bridging to provide redundancy.  Now the problem is, when i 'no shut' both ports on the router connected to the switches, it all works well for 20secs and i can even ping succesfully, but then is comes up saying that the po1 port is flapping with port such and such and then both ports goto into err-disabled mode. I was wondering how i get around that??  Or is there another way to try and get 2 ports on the same router to be able to use the same default-gateway.

Cheers
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Question by:Thunder-Cat
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6 Comments
 
LVL 21

Assisted Solution

by:from_exp
from_exp earned 800 total points
ID: 22819716
possibly you have created a loop within your network.
do you have spanning tree enabled?
what is your network topology?
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Author Comment

by:Thunder-Cat
ID: 22820273
hey thanks for the reply, the topo is a c7000 connected to a router via two switches in parallel for redundancy and the trunk ports from the switches to the router have spanning-tree portfast trunk enabled.  when i type "sh bridge" on the router no mac addresses appear.
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LVL 16

Assisted Solution

by:Aaron Street
Aaron Street earned 800 total points
ID: 22820425
you dont want port fast!!!

that shoudl only ever be used on access ports to connect host devices to!!

never switch to switch ports!
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LVL 21

Assisted Solution

by:from_exp
from_exp earned 800 total points
ID: 22820439
hmmm, spanning tree port fast should be disabled on non-end ports....
if c7000 is hp blade chassis, then what kind of network modules do you have?
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LVL 16

Assisted Solution

by:Aaron Street
Aaron Street earned 800 total points
ID: 22820444
ps see your other question.

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Accepted Solution

by:
Thunder-Cat earned 0 total points
ID: 23294068
I figured it out i ended up taking port-channelling off the switchports going to the router and it stopped flapping.
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