How to create a switching loop in a lab environment?

Dudes!

I'm going through my BCMSN now and I was wondering if anyone knew the best way to create a switching loop. I want to experience a switching loop in my lab so that I can detect one more easily in my production network at work.

I have the following:
1x 3550
2x 2950

I want to be able to see the switching loop in action (with debugs and show commands, etc.). Has anyone done this? Any suggestions?

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Comments

nicklauscombs

turn off spanning tree?

tomset

nicklauscombs wrote:

turn off spanning tree?

Let's say I have 2 2950s connected together with 2 trunks and I turn off spanning tree. If I then connect 2 PCs to the switches (1 to each switch) and have 1 of them send a broadcast, how would I be able to tell that a switching loop is occurring?

networker050184

Sniff the traffic and if you see the same frame multiple times you know you have a loop.

billyr

As above.
Alternatively, turn off spanning tree, set up your 2 p.c's to use dhcp and wait a while for them to send out their broadcasts and for the loops to occur.
If you dont have a packet sniffer. Press the mode button on your 2950 until it gets to Util.
Each port light now lit up tells you the percentage now being utilized by your switch. I think with a 24 port switch each port equates to roughly 4% or there abouts. With only a couple of p.c's connected you shouldn't be lit up very far.
If a broadcast storm is occuring then you should see plenty of activity.

tomset

billyr wrote:

As above.
Alternatively, turn off spanning tree, set up your 2 p.c's to use dhcp and wait a while for them to send out their broadcasts and for the loops to occur.
If you dont have a packet sniffer. Press the mode button on your 2950 until it gets to Util.
Each port light now lit up tells you the percentage now being utilized by your switch. I think with a 24 port switch each port equates to roughly 4% or there abouts. With only a couple of p.c's connected you shouldn't be lit up very far.
If a broadcast storm is occuring then you should see plenty of activity.

Good advice, thanks!