Question on STP when connecting 2960 with Alpine

[tselvan]

Hi All,

I am trying to connect 2960 switches to the extreme Alpine switches.

As per the diagram below,STP is not running in the alpines.I am not very sure whether STP should be enabled in this scenario to avoid any loops.

All suggestions are appreciated.

Note:

Both Alpines are connected as trunk links.

Both 2960's are connected using Fasethernet ports as Trunk using port-channel

Then each Alpine to 2960's using the Gig interface.

Thanks

[Trunk]

Alpine---------------Alpine

| |

| [Trunk] |

2960---------------- 2960

[Aaron Harrison]

Hi

The picture isn't terribly clear but your verbal description says that the two Alpines are connected to each other, and the two 2960s are connected to each other. Also that each Alpine is connected to a 2960.

I guess that the diagram should look like a square?

A square is just a loop with corners, so you definately want STP enabled - there are not many situations where it's recommended to disable it.

Make sure you have portfast turned on (or it's equivalent on the Aplines) on user ports and there should be no negative effects of turning it on.

Regards

Aaron

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[tselvan]

Hi Aaron,

Thanks for your inputs.Sorry for the bad picture.

Yea it exactly looks like a square,but in the Alpines STP is disabled.So I am a bit concerned whether to enable to it in 2960's.Any comments on this?

Thanks

[globalnettech]

Hello,

with your current setup, and provided that all links are up, your network, at least in theory, should have a loop, and hence should not work. Is this a live situation, and do you experience performance problems ? In any case you should turn STP on on all links between the 4 switches, as the previous post suggested...

Regards,

GNT

[Francois Tallet]

It all depends on what these alpines are doing when STP is disabled on them. If they flood BPDUs like user traffic, then they will both look like a unique hub to the 2960 and STP will be able to block the loop on one of the 2960. Convergence will be slow in case of link failure.

If you don't run STP on the 2960 (or at least one of them;-)) or if the alpines are dropping the BPDUs sent by the 2960s, then you'll have a permanent loop.

Regards,

Francois