STP - Changing link speeds & affecting topology

As the topic suggests, can you completely change your STP topology by setting a link that was a '19' path to a '100' via the speed?

So I set speed at both of the links as 10Mbit (they were a-100), how does that affect the port cost in the STP process? It doesn't, according to my Boson lab.

Is this expected behaviour or should it modify the cost pronto and thus change my STP topology?

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Comments

EdTheLad

The bandwidth configured on the port is what spanning-tree uses. Modify the bandwidth to modify the spanning-tree cost.

Magic Johnson

Another question, if you set the root switch using the 'root primary' command and let your switches converge, I accidentally pressed up and enter thinking there was a different command but it was the 'root primary' one, even though it was the exact same command it made my entire network converge again. Is that expected behavior or just Boson sim?

Eurgh wish I had a real lab at this point.

Magic Johnson

EdTheLad wrote: »

The bandwidth configured on the port is what spanning-tree uses. Modify the bandwidth to modify the spanning-tree cost.

First page of my notes. /facepalm

This is such a large, intricate topic with so many gotchas I feel like I'm constantly forgetting and re-going over things!

EdTheLad

Sounds like strange behavior. You wish you had real equipment? how about using gns, no excuses for using a crappy application like boson. You're wasting your time....

Magic Johnson

EdTheLad wrote: »

Sounds like strange behavior. You wish you had real equipment? how about using gns, no excuses for using a crappy application like boson. You're wasting your time....

I gave GNS a try, but the real issue for me was getting the iOS images (even through...incorrect means), I did manage to get one but it was ancient and didn't have a lot of commands that 15.1 has.

Boson is ok to be fair, the pre-compiled labs and exercises are a big winning point for me, however in scenarios like this having real kit so there is no doubt in behaviour would be massively beneficial.

broli720

You could always get packet tracer.

EdTheLad

I think you should make it your mission to get GNS3 running with enterprise code, doesn't need to be 15.x ios, there are loads of ios versions floating on the net. It might take 1 day to get up ad running, after you wont look back. You can still use your boson labs, but you are making a huge mistake continuing as you are. You will miss out on commands,behavior, debugs etc... I tried boson for one day and it was enough for me, if you are happily working away with it, you are not labbing properly.

Magic Johnson

broli720 wrote: »

You could always get packet tracer.

That's much the same as Boson netsim I've found.

Magic Johnson

EdTheLad wrote: »

I think you should make it your mission to get GNS3 running with enterprise code, doesn't need to be 15.x ios, there are loads of ios versions floating on the net. It might take 1 day to get up ad running, after you wont look back. You can still use your boson labs, but you are making a huge mistake continuing as you are. You will miss out on commands,behavior, debugs etc... I tried boson for one day and it was enough for me, if you are happily working away with it, you are not labbing properly.

Can you do layer 2 stuff in Boson? I thought it was just routing?

johnwest43

You cant go wrong with real equipment! just hit up ebay for a couple 2950's and maybe a 3550. should cost more than $150 for all three. Nothing beats real hardware when it comes to switching.

EdTheLad

Magic Johnson wrote: »

Can you do layer 2 stuff in Boson? I thought it was just routing?

Yes you can do some layer 2 in GNS , i actually use IOU which is a level up from GNS. I really cant believe in this day and age people are still using boson and other ios hacks when free emulators are available.

Magic Johnson

EdTheLad wrote: »

Yes you can do some layer 2 in GNS , i actually use IOU which is a level up from GNS. I really cant believe in this day and age people are still using boson and other ios hacks when free emulators are available.

I looked a little harder this time and got some decent iOS images and set it up in GNS3.

You can do VLANs and stuff but can't actually get in to command line for the switches (as far as I can see?). I'll definitely utilise this for routing.

The reason I went with Boson was because it helped me through ICND1 and I thought it was pretty good. Also came as a deal with the EXSim practice tests, which were great.

Real hardware would be perfect I agree but I am completely broke at the moment so unfortunately it is not an option.

So I think we're a bit off topic! Haha.

Magic Johnson

EdTheLad wrote: »

The bandwidth configured on the port is what spanning-tree uses. Modify the bandwidth to modify the spanning-tree cost.

More SIM woes:

I changed interface speeds as described in Boson, with absolutely no effect on the STP topology as described in the OP. However in PT I just changed a fast ethernet port to be speed 10 and it immediately changed my STP topology, the port cost changed to 100 and set off the LRN/LIS process.

EdTheLad

Did changing the speed change the BW on the interface? It possibly does, i cant test this on real equipment, but all you have to know is that the spanning-tree cost is bandwidth dependent.

Magic Johnson

EdTheLad wrote: »

Did changing the speed change the BW on the interface? It possibly does, i cant test this on real equipment, but all you have to know is that the spanning-tree cost is bandwidth dependent.

Aye it did, checked under the interface command it was 10000. I was trying to use the 'bandwidth' command on the switches then remembered it only applies on serial interfaces lol.

Well, I'm not sure why it doesn't under Boson, in fact changing the speed doesn't affect the B/W at all, which is why it wasn't changing my STP topology!

Grr!

EdTheLad

It applies to all routed interfaces, serial, ethernet, port-channels etc

Magic Johnson

EdTheLad wrote: »

It applies to all routed interfaces, serial, ethernet, port-channels etc

Ah, so only for L3 switches then? Just checked on PT I can change BW on L3 but not L2 switches.

EdTheLad

Forget what i said about routed lol, busy with something else. It will depend on what hardware you have, generally with spanning-tree you will modify spanning-tree cost. Cant think of any other reason why you would change bw on a layer 2 device. Bw is used for routing protocols and l3 qos config.

Magic Johnson

EdTheLad wrote: »

Forget what i said about routed lol, busy with something else. It will depend on what hardware you have, generally with spanning-tree you will modify spanning-tree cost. Cant think of any other reason why you would change bw on a layer 2 device. Bw is used for routing protocols and l3 qos config.

To experiment! Haha. Just to see the behaviour, I'm a nosey so and so that way.

I logged a call with Boson about changing speed and it not changing BW.