Do we need STP (spanning tree protocol)?

[ritavkalmthout]

We have a small network. Two 2950T-24 switches, one (Novell) server. The switches are connected through 1 of the Gigabit ports.

The network is very simple:

- about 30 Client-PC's connected directly to a port

- one Cisco router to a port for internet access

- some client-pc's connected through a hub

- no 'redundancy' connections are made

We have set some ports to PortFast because of some problems in logging in.

Still the network seems slow, and a lot of STP messages are generated by the switches, which none of our other devices understand.

DO WE NEED STP?

Thanks in advance,

Rita van Kalmthout

Rena Electronica B.V.

[jamey]

STP only comes into play when there is a loop in the network. In your case, there is no loop as only one connection is used to connect your switches, therefore, STP is not in effect.

If you connected your switches together via two Gigabit connections, STP would kick in and disable on of the ports to avoid a loop.

I think you need to look at other parts of your network to determine the source of slowdown. What specifically is slow? Have you check the cpu % on your server and switches? How's the memory usage look on the Novell box? Are all parts of the network slow or just client to server? Things like this...

My $.02

-HTH

[ritavkalmthout]

Can I log traffic amounts etc. in our 2950 catalyst switches. If yes: how can I do this.

[thisisshanky]

As long as you have no redundant connections, you dont really need STP. But its not a good idea to disable STP, because anybody could add a rogue switch and create loops on your network without your knowledge. When you enable portfast on the access ports, Topology change BPDUs are not sent on that port when the port state changes.

Are you running IPX on the Novell server ? IPX is a very chatty protocol. You might want to divide your network into vlans and keep the IPX devices on their own vlan.

[robho]

I recommend keeping STP enabled. There is no sense in disabling it in a properly designed network. I see no disadvantage other than the delay of a link-up situation which can be worked around by enabling portfast.

For the network slow issue, I suspect a bottleneck between the switch and router. Check to make sure that it is full-duplex on both ends and no errors are incrementing.

[ritavkalmthout]

Thanks, but I still hav a question left:

What happens when I connect a hub to a port that is set as PortFast. When I see that my network is not redundant, I think it's not a problem because no loops can be created. But reading documentation it says: the portfast feature should never be used on switch ports that connect to other switches, hubs or routers.

[robho]

The documentation is correct. It is "recommended" not to enable it on a hub. This is to avoid a L2 loop in case the hub is accidentally patched to 2 different switchports configured with the portfast feature.

With that said, you should not have any STP delay if the setup is: PC --> HUB --> Switchport. The reason is that when the PC is powered down, the hub keeps the switchport up and the port does not need to go through the stp transition states.

You should only enable portfast on ports where servers/workstations are directly connected.