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Ask the Expert- SD-WAN


Disabling STP

I am newbie, I wanted to know how to disable STP on a layer 2 switch like 2900 series. Any reference link is also appreciated.


Re: Disabling STP

Do you understand the potential pitfalls of disabling STP? Why would you want to disable it? Even if your network is free of physical loops it is always recommended to leave STP on for those days when someone inadvertently (or even intentionally) introduces a physical loop in your network and you spend hours troubleshooting what happened all of a sudden.

That being said the following link will show you how to disable it on the 2950 series switches:


Re: Disabling STP

This is for one of my client who is using a Switch of different brand whose command is very close of Cisco IOS and features are as same as 2900 Series, except the that All the Ports are of Gigabit Standard. I do found 'no spanningtree' option after your post in that swtich, and disabled it. However I now wonder if disabling STP would resolve his (i.e. my client's) purpose. Here are more details on that case.

My client have a particular application that he is hoping to accomplish with the Switch. He wants to "mirror" traffic on a gigabit link off of another switch and feed it into to this Switch and broadcast the traffic out (via VLAN port assignments) to multiple ports for further analysis.

The problem we have is that the mirroring switch retains the Layer 2 MAC information on the gigabit link that my client want to monitor. So when the mirroring device (remote switch uplinked) pushes the copied traffic into the feed on the switch, the switch learns the location of the two MACs as being on the interface of the mirror/feed port. That creates a problem.

On the unicast packets, the destination MAC on packets on one of the directional streams is the source MAC on the stream of data in the other direction. The switch then promptly drops all of the unicast traffic because 802.1d address learning will not permit the packets to be forwarded (broadcast traffic forwards just fine, but we want *all* of the traffic to be forwarded to the Intrusion Detection System sensors, not just part of the traffic).

So, ideally if I can disable 802.1d address learning on the switch, I thought I would accomplish this. This scenario can be easily dealt if I had a Gigabit Hub (Gigabit only, NOT 10/100/1000 Hub). I just want the Switch to behave like a hub with ports set to no-negotiation with Speed / Duplex Settings of 1000Full.

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