How to create a switching loop in a lab environment?

tomset

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?

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!