pkt trcr root id

[tradell]

Why in packet tracer, in my 3 switch lab from chapter 8, in my show spanning tree on each switch, 3 different mac ids, neither of them matching the root id . . .?

And how do you retain this book’s info in your brain for the ccna exam . . .? I take a week off, and I can’t believe the stuff I need to review again to re-fresh my mind !!!!

There was a point when I felt like I had 80% of the book down. Now I feel like I'm around less than ½. Of course it comes back easy enough with a little review. Its frustrating when I try to recall something, and it’s just not there!!! Especially, when the last I knew, I had it down . . .!!!

thanks !

[Big Evil]

Mate, we have all been here, it is called "grey matter". I read once you have read something at least seven times before it is commited to your long term memory. Last week i had to do a password recovery on a switch, i carry the Cisco PDF of this on my USB pen for this as i always forget!! I don't do it enough.

Yes the exam is different as you cannot use documents to get your way through like you can in the real world. Some parts will stick quicker and some parts will not. The only weakness is not being able to see your weak areas and knowing they are weak, kinda like fooling yourself "yeah i know that" when really you do not.

Read the first part of your post and you will see you have seen an error and questioned it, that itself shows you are on the right track.

HTH.

[tradell]

I don't see my error in the first part of my post.

Though I do see where the root id mac is coming from, not that it makes any sense to me!

The phone off my S1 switch is the MAC which is diplayed as the root on all my switches when I show spanning-tree on each. How does that happen ?

Or am I not properly understanding the show spanning-tree output ?

[Big Evil]

Re-read what i wrote mate. I said you have "seen an error", meaning you have not taken what the switch has told you as granted. Not you post is an error.

[tradell]

The way I understand it, the mac in red (is a phone) is supposed to be the mac of the root switch.

The underlined mac is of the switch which the "show spanning-tree" command was executed from. 7 is the designated port of same switch to root.

I'm not seeing what I am missing . .


VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0003.E434.0066
Cost 19
Port 7(FastEthernet0/7)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 00E0.F935.7AE0
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20

Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19 128.1 P2p
Fa0/3 Desg FWD 19 128.3 P2p
Fa0/7 Root FWD 19 128.7 P2p
Fa0/8 Altn BLK 19 128.8 P2p

[Fuzz]

What is the output of sh spann on the root switch?

[tradell]

That's the issue. I can't do a show spanning-tree on a host. As previously stated, the mac shown as the root, belongs to a phone.

Anyway, I deleted the phone. Finally, one of my switches became listed as the root. I then re-introduced the phone into the network, and yes, my root switch remained the root.

Now I just have to change the vlan priority on my Core switch so that it will be the root.

[Fuzz]

Remember that a phone has an inbuilt switch with three ports - one to the access layer switch, one to the PC and an internal one to the phone. If the MAC address of the phone is the lowest of all the devices, it will assign itself as the root bridge. This is how you got confused - the output on the CLI wasn't incorrect, and neither was your understanding of the spanning tree topology.

Which switch did you think should have been the root? (this is where I was trying to point you with my last question)

[tradell]

OK. . . sanity restored !!! I see and understand the phone having a built in switch from the telephony section of the vlan chapter 9.

My S1 (chap 8 diagram) has the lowest priority/mac combo, which is now verified by the "show spanning-tree" command on S1. As I said, I will have to change the priority on my Core for it to be the root.

So, in real life, what would you do . . . ? Can you change the mac of a phone . . . ? In pkt trcr, I just removed the phone. I don't think you'd want to be changing switch priorities just to accomodate host devices . . .Portfast . . . . ?

[Fuzz]

It seems you may have missed the point of having a root bridge. You do want to change switch priorities. Phones aside, you have no idea what the MAC address of a new switch is going to be when you add it to your production network. It could be the lowest value in your network, and therefore advertise itself as root. If this switch is an access layer switch, your traffic will start to take some odd paths through the network - something you really dont want.

You are the administrator, you want to be in control of how data flows through your network. You should set the priorities of every switch you need to to make sure the data flows the way you want it to. There are more features to help you with this - STP is a huge topic for CCNP, tuning, and even securing, convergence has great importance in switched networks. If you can't control the traffic flow, you can't tune your network.

Have a look at my blog on STP tuning for a quick overview.

http://altarespot.lessergods.eu/?p=43

[tradell]

True, I may not yet fully understand having a root bridge. Though off the top of my head, efficient convergence and path selection regarding bandwidth would be at the top of my list.

Yes, phone aside, I see the importance of the ability of maintaining switch priority.
Phone not aside, I can’t imagine an administrator juggling networking device priorities to accommodate host devices on a continual basis.
Remember, I’m stating this due to my chapter 8 excercise with S1, S2, and Core. My host phoneA off S1 took root from each S1,S2, and Core points of view.

[Fuzz]

You wont be juggling switch priorities around - if you configure the switch priorities in the first instance. If you set your root switch priority to 0 or 4096, no other switch, phone, device, anything, can then advertise itself as the root switch.

You set the priority once, then forget about it (figuratively speaking).

The reason your phone was showing as the root switch was because all your switches had default priorities (32768) so the lowest MAC address won the bid. Your root (core) switch should not have a default priority!

[tradell]

ahhh....that would make better sense !

awesome. . thank you !