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04-27-2017 11:06 AM - edited 03-08-2019 10:22 AM
Hello Network Gurus,
I noticed network flapping between g1/0/1 and g1/0/2
Both has stp portfast configuration
on g1/0/1 a dummie switch has been connected. Could it cause the network flap?
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04-27-2017 12:39 PM
John,
in general, you never want to set portfast on a port where a switch is connected to, managed or unmanaged. Unmanaged is probably even worse because you cannot even control or configure whether or not it becomes the root switch.

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04-27-2017 11:13 AM
Hello,
what is connected to G1/0/2 ? Could be a spanning tree issue...
Is the 'dummie switch' running STP ?
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04-27-2017 11:21 AM
Hi Georg,
The dummie switch I was referring to was an unmanaged netgear switch so I can connect more host using that port. A regular pc is connected to g1/0/2.
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04-27-2017 11:41 AM
Hello,
what do the logs on the switch show ? Depending on the physical setup of your network, if you have only 1 Vlan, you could try and turn spanning tree off for that Vlan, using the command:
no spanning-tree vlan x
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04-27-2017 12:00 PM
I was thinking of disabling the spanning tree port fast...what do you think? I'm just learning this so...I found some articles regarding portfast but still unsure..
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04-27-2017 12:03 PM
Ok Greg, don't laugh but the flapping log I found was date Dec. 18 ugh LMAO unless my time is somewhat messed up.
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04-27-2017 12:16 PM
Hello John,
so nothing is currently flapping ?
Spanning-tree portfast by the way means that the port goes into forwarding immediately instead of going through the listening and learning states first. It is generally used for access ports with end hosts attached.
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04-27-2017 12:34 PM
Looks like it, I just saw it on my network log that says flapping I didn't even pay attention to the date which is Dec. 18.
Some network guys are saying that if portfast is set and an unmanaged switch is connected, then an issue could arise.
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04-27-2017 12:39 PM
John,
in general, you never want to set portfast on a port where a switch is connected to, managed or unmanaged. Unmanaged is probably even worse because you cannot even control or configure whether or not it becomes the root switch.
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04-27-2017 12:53 PM
Thanks Georg! Your input greatly help on what I'm working on.
