Packet Tracer/Spanning Tree Issue

Ok, I had some spare time at work today and decided to mess around with packet tracer a little bit. I ran into a problem, if you look at the screen shot you will see a redundant switched network at the lower right hand side. There is a constant broadcast storm once spanning-tree begins forwarding ports.

Spanning tree seems confused as to which switch is suppose to be the root for vlans 1-3. Now I know what you are thinking, but yes I did (or attempted to) manually set the root bridge. CA_SW1 has its priority set to 0 for vlans 1-100.

What I think the problem is, it seems like every one of these switches have the exact same MAC addy. I assigned different priorities to each switch, incrementing up from 0 to 4096 to 8192...etc, thinking that would fix something....nada.

Any ideas? I have hosted the packet tracer from my skydrive if you want to play with it.

http://cid-8177b48068b05452.office.live.com/self.aspx/.Public/Messing^_Around.pkt

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Priston

You have 2 switchs with the same hostname
display name CA_ACC_SW2 is hostname CA_ACC_SW1

alan2308

Priston wrote: »

You have 2 switchs with the same hostname
display name CA_ACC_SW2 is hostname CA_ACC_SW1

That shouldn't matter, when you first turn everything on, every switch has a hostname of Switch.

For some reason, on VLAN 2, VLAN2_ACC3 and VLAN2_ACC4 have both ports forwarding. Every other switch looks ok here. I'm not seeing the issue with every switch having the same MAC address, and CA_SW1 does appear to be the root bridge for all VLAN's. My initial thought is a PT bug as I don't see anything in your configs that would cause that. But I don't have 11 physical switches to duplicate your topology.

I'm using PT 5.3.1 FWIW.

Monkerz

alan2308 wrote: »

That shouldn't matter, when you first turn everything on, every switch has a hostname of Switch.

For some reason, on VLAN 2, VLAN2_ACC3 and VLAN2_ACC4 have both ports forwarding. Every other switch looks ok here. I'm not seeing the issue with every switch having the same MAC address, and CA_SW1 does appear to be the root bridge for all VLAN's. My initial thought is a PT bug as I don't see anything in your configs that would cause that. But I don't have 11 physical switches to duplicate your topology.

I'm using PT 5.3.1 FWIW.

Maybe just a bug with my version. I am using v5.1. This is what I see for CA_SW1:

CA_SW1#sh span
VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority 1
Address 0030.A3BA.9B12
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 1 (priority 0 sys-id-ext 1)
Address 0030.A3BA.9B12
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
Fa0/2 Desg FWD 19 128.2 P2p
Gi1/1 Desg FWD 19 128.25 P2p

VLAN0002
Spanning tree enabled protocol rstp
Root ID Priority 1
Address 0030.A3BA.9B12
Cost 19
Port 1(FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 2 (priority 0 sys-id-ext 2)
Address 0030.A3BA.9B12
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20

Interface Role Sts Cost Prio.Nbr Type
---- ---
Fa0/1 Altn FWD 19 128.1 P2p
Fa0/2 Desg FWD 19 128.2 P2p
Gi1/1 Desg FWD 19 128.25 P2p

VLAN0003
Spanning tree enabled protocol rstp
Root ID Priority 1
Address 0030.A3BA.9B12
Cost 19
Port 1(FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 3 (priority 0 sys-id-ext 3)
Address 0030.A3BA.9B12
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
Fa0/2 Altn BLK 19 128.2 P2p
Gi1/1 Desg FWD 19 128.25 P2p

When I try to trace down the root for VLAN2 and VLAN3, it sends me in a circle;
CA_SW1 -> CA_ACC_SW1 -> VLAN2_ACC1 -> CA_ACC_SW2 -> VLAN2_ACC1

Monkerz

Ok, just downloaded PT v 5.3 and now CA_SW1 is showing as root for all VLANs, but VLAN2_ACC2, VLAN2_ACC3 and VLAN2_ACC4 has both ports forwarding like you saw.

mikej412

Take any unexpected result in a simulator with a grain of salt.

I put it in simulation mode and watched about 5 seconds worth of all packets and 10 seconds worth of STP packets and didn't see a loop.

With simulators save your network, close and reopen. Repeat until you get the desired/expected result -- or give up or try it on real hardware.

mikej412

Monkerz wrote: »

Ok, just downloaded PT v 5.3 and now CA_SW1 is showing as root for all VLANs, but VLAN2_ACC2, VLAN2_ACC3 and VLAN2_ACC4 has both ports forwarding like you saw.

I'm using 5.3 -- CA_SW1 is root for all VLANs.

I only see VLAN2_ACC3 with both ports forwarding, VLAN2_ACC4 only has the 1 port forwarding.

If there are multiple 5.3 builds, I'm probably on an earlier build -- which would mean they are adding software bugs instead of removing software bugs.

gregorio323

usually packet tracer is bugged when it comes to STP you have to save and restart.

Monkerz

mikej412 wrote: »

With simulators save your network, close and reopen. Repeat until you get the desired/expected result -- or give up or try it on real hardware.

This is really just for fun or the sake of doing it. Unfortunately, my wallet is not as large as my imagination, so I have to resort to simulator/emulators. Of course I do have a few switches and routers to play with, but while on a conference call or upgrade bridge boredom sets in and I can't really walk into our noisy data center to tinker with my lab.

I do have GNS3, which works great for routing emulation, but unless I am mistaken it does not really support switching.

If anyone has any ideas or good emulation software (free or $$), I'd like to give it a try.

alan2308

Monkerz wrote: »

This is really just for fun or the sake of doing it. Unfortunately, my wallet is not as large as my imagination, so I have to resort to simulator/emulators. Of course I do have a few switches and routers to play with, but while on a conference call or upgrade bridge boredom sets in and I can't really walk into our noisy data center to tinker with my lab.

I do have GNS3, which works great for routing emulation, but unless I am mistaken it does not really support switching.

If anyone has any ideas or good emulation software (free or $$), I'd like to give it a try.

You can slap a NM16esw into a router and do quite a bit of switching. And here is a list of what it can't do.

Free CCNA Workbook is able to cover nearly all of the CCNA topics with GNS3, so it's more capable than you might think.

Monkerz

Well then, I retract my previous statement.

mikej412

Monkerz wrote: »

If anyone has any ideas or good emulation software (free or $$), I'd like to give it a try.

Dynamips (with the Dynagen or GNS3 front ends) is about as good as you're going to get. At least there you're dealing with the actual Switch Module limitations (and hardware simulation in Dynamips).

Boson has been around for a while -- so if they didn't add to many bugs for version 8.x of their simulator it may work better for switching than Packet Tracer.

Someday Packet Tracer may become a full CCNA network simulation solution -- but it's still not there. And it still has bugs.

There's also Mimic. I think they've added an online option -- but I'm not sure if you're just stuck with their canned network(s) or if you can build your own. I tried their recent demo (and the iPhone app) but their web site was having issues and I haven't been back to try again. In the past it was outrageously expensive -- but the online access price seems more reasonable now (if it works).

You can get the "Cisco Press Simulator" -- which seem to just be flash based exercises to run through. It's not a build your own network and go wild type thing like Dynamips/Boson/Packet Tracer.

Monkerz

Thanks Mike!

alan2308

I immediately thought of this thread when I came across this blog post tonight. A Spanning Tree/PVST LAB in GNS3.

The Net: Spanning tree, PVST lab - GNS3