Spanning Tree Protocol Question

[munyeephang]

Dear all,

I'm still new to STP technology.Would appreciate if someone can help me with this:

1. If I have two switches connected to one another, how would I know that the STP is running fine and that the STP is in place? Would I know that there is no loop/broadcast storm happening between the two switches?

2. If I have two devices

-------Device A--------

| |

|

Switch X Switch B

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|

[amit-singh]

Hi,

STP is a layer-2 protocol which is used to provide a loop free network by putting the redundent links (which can create a loop) into blocking state thus providing redundency when a link fails.

So with in ur 2 switches connect the redundent links and STP will definately block one of the links taking its algorithm into account. This shows that the STP is working on those ports and that switch.

Didnt get ur 2nd question exactly.

Please refer the following links:

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12120ea2/2950scg/swstp.htm

HTH,

-amit singh

[munyeephang]

Hi Amit,

Thanks for the reply. Sorry for the incomplete question.

As the 1st question , how would I know that the STP is running fine with the setup below? Would I see any difference in the behaviour of the switches ?

|----------------------------|

| |

Switch X Switch Y ---LAN

| |

|----------------------------|

As the second question , how would I know that the STP is running fine with the setup below? Would I see any difference in the behaviour of the switches ?

|-----------Device A---------|

| |

Switch X Switch Y ---LAN

| |

|-----------Device B---------|

Regards,

Munyee

[Georg Pauwen]

Hello,

the easiest way to verify if Spanning-Tree is running is to issue the command ´show spanning-tree x´ (where x is the VLAN for which you are verifying the STP status). If you are running CatOS, the command is ´show spantree x´.

After you issue this command, you should see the following line at the top:

For IOS:

Switch#show spanning-tree 1

Bridge group 1 is executing the VLAN Bridge compatible Spanning Tree Protocol

For CatOS:

Console> (enable) show spantree 1003

VLAN 1003

Spanning tree enabled

This command also tells you which ports are forwarding, and which ports are blocked (hence ensuring a loop-free topology).

Regarding the broadcast storm, there is not really a command to verify that one is occurring. The symptoms of a broadcast storm include network response times that become extremely slow and network operations that are timing out. As a broadcast storm progresses, users might not be able to log in to servers or access e-mail. As the storm worsens, the network becomes unusable.

A useful way to recognize a broadcast storm is to monitor the percentage of broadcast and multicast traffic when your network is operating normally, . You can then use this data as a baseline to determine when broadcast and multicast traffic is too high.

Does that answer your question ?

Regards,

GP

[munyeephang]

Hi GP,

Thanks for the reply. Are there any tools which I can use to get the baseline of broadcast and multicast to recognise a broadcast storm as you suggested?

I need to recognise this broadcast storm because two firewalls which I have connected in between the two switches as described earlier in the post begin to reboot themselves as soon as I connect them together to the two switches. I would like to do High Availability for the network, but now that the FW keep rebooting , we're wondering if it's the problem with the STP in the switches.

your comment?

Regards,

Munyee

[jroyster]

You'll know when you have a loop or broadcast/multicast storm. Mainly because everything will just stop working. ;^)

To really verify you can telnet or console into a switch, clear the couters and look at the number of broadcasts.