On Sat, 29 Nov 2003, Christopher Dawkins wrote:
Yes, redundant links are, I am building up a number, and I have looked at STP. The main reason I haven't used it is that I prefer the idea of subnets, routed, RIP and routers instead: routers based on multi-port FreeBSD boxes. I don't see how STP (or subnets) cure this switch-jamming problem, except that the more intelligent the device the more capable it is of preventing the jam from spreading back onto the network spine. However, we have some quite large (multi-building) branches containing hundreds of outlets that are all within the same easily-jammed area.
Hi,
Spanning Tree is a level 2 protocol where as RIP is a level 3 protocol. Ie Spanning tree works at MAC address(Ethernet), RIP works on IP address(TCP/IP level).
A switch in a Spanning Tree network learns the MAC address of other devices attached. If it detects a loop, it will automatically block one of the lines that are feeding into it. A master hub has to be defined in the system. This is done by setting a prioritory level ( believe it's between 0-65535). If all switches are set to the same priority it will automatically work out which device has the lowest mac address and use that as master.
For example
____ | 1 | |____| / \ / \ ___ / \ ___ | 2 |____________| 3 | |___| |___|
Hub 3 has two alternate paths to talk to hub one, either directly or via hub 2. This would cause a loop situation, as you are already aware. Using Spanning Tree, Hub 3 would automatically block all data on either the port that connects it to hub 1 or hub 2. This would depend on the spanning tree prioritory set in each of the hubs. If Hub 1 had a prioritory of 1, hub 3 would block all data from hub 2, so all data would go via hub 1. If hub 1 were to fail, the block would be automatically removed.
That is how I remember it working when I did the course in configuring Foundry Routers and switches a few months ago.
Hope that helps
Chris
Chris *************************************************************************** E Mail Chris@glovercc.clara.co.uk WWW http://www.glovercc.clara.co.uk Someday, we'll look back on this, laugh nervously and change the subject. -Anon