Every single time! broadcast storm....

Ok well as im studying for CCNA been messing around with a few topologies and of of them ive been trying is the following:

S1 to S2
S2 to S3
S3 to S1

so a triangle like topology, but i have 2 links running to each switch, each time i set this up i think im creating a broadcast storm, but PT keeps freezing on me, so i cant really investigate.

The way i set it up is,

Connect all the cables first.
Configure S1, Configure Vlans and assign switch-ports, then configure VTP.
then configure the trunk links
I then enable RapidSpantree, move onto switch 2 to change the vtp mode to client.

As soon as i start to enable the trunk links the nightmare starts to happen!

Was wondering what i was doing wrong? Obviously i know that one/multiple ports are no longer in a blocking state but is there a specific method, i have to do to avoid this happening?

Am i enabling trunk links too fast? i know normal Span tree takes a while to converge??

any advice would be great.

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Comments

networker050184

What makes you think you are creating a broadcast storm?

DANMOH009

Its a combination of a couple of things really.

1. All the links on PT go dark green, rather then the normal light green, plus there orange links (which are represented by PT as a port in blocking state) dissapear.

2. Plus a debug on VTP updates just freezes the system completely.

3. and if i get a chance to click on simulation i can see the vtp update packets all over the place.

***

It might be worth noting that i fixed this by rebooting all the switches and had them all converge again! Even though it is fixed now, is there any reason this would happed? could it be down to just enabling the trunk links too quick, i notice that when i enabled the trunk links the links went into and up/down or down up state.

MickQ

Probably a bug in PT. It is a simulator, after all.
Whenever I've had problems with it, where I know a command should work, but isn't, I save the config and reload the devices. If that doesn't work, I restart PT.

I've had to do that on a few obscure setups in PT (for uni) where it's working perfectly in GNS3.

DANMOH009

Ye probably, just wondering though when you change a access link to a trunk link, does it have to change the link status to down up? And if so could the links going down and then up cause span tree to re coverage??

MickQ

Think about it. You're causing a change in the link.
What's STP meant to do?
Which STP version are you running, what are its features?
What's the purpose of portfast (if that's on your course)?

Understand the idea behind the technology, and then get (quite rightly) pissed off at it not working properly in the simulator

Btw, if you're planning on hanging around in networking for a while, it's worth getting several switches (even cheap ones) for playing with and testing out your theories.

jdballinger

Also remember that STP is enabled by default on Cisco switches, so unless you turn it off a broadcast storm is highly unlikely.