Help needed about Implementation of "Spanning Tree Protocol" for switch

In article , GS wrote: :A switch contains 3 uplinks which are on WAN side and there 30 LAN :ports for subscriber side, how to implement Spanning tree protocol :(802.1d) in this switch?. Can somebody suggest how to implement STP and :what are the things has to take care on interface level?. Thanks in :advance. We have chip called "xyz" which inter connects WAN and LAN.

Sorry, GS, your question looks suspiciously like a course assignment.

If you are actually working for a company that designs switches, then I would expect you to have read the appropriate RFCs throroughly and to ask -specific- questions -- and I would expect that the company would have hired someone who had switch design experience.

Actually I am looking for some info about how spanning tree protocol can be interfaced with WAN and LAN ports?, that's all I needed.

In article , GS wrote: :Actually I am looking for some info about how spanning tree protocol :can be interfaced with WAN and LAN ports?, that's all I needed.

The Spanning Tree Protocol doesn't care whether a port is a WAN or LAN port. You can send BPDU on a WAN link.

Whether it is worth sending BPDUs or not depends upon whether there is any possibility that the far hop of the WAN link might have topology loops that you need to arbitrate between.

Perhaps you are asking about a different matter, which is to say tunneling of BPDUs over WAN links, so that you can have an extended "layer 2" path resolution instead of using a "routing" path resolution? If that's what you are trying to do, then this article might be of interest:

This whole STP/Bridge implementtaion does really care about hardware interfaces (physical ports)? Or is it everything is in software only, for example, if the port's state is changed (if the port is got disconnected)?. Thanks.

In article , GS wrote: :This whole STP/Bridge implementtaion does really care about hardware :interfaces (physical ports)? Or is it everything is in software only, :for example, if the port's state is changed (if the port is got :disconnected)?. Thanks.

I'm still not sure what you are trying to do.

STP is a layer 2 protocol, not a routed protocol. If you have a WAN port which is transmitting BPDU's to you, then the STP information so carried will be taken into account in the construction of the tree.

If you had a situation where you had multiple WAN connections that were linked together at layer 2 on the remote end and so were determined by STP to be part of the same tree, then because WAN links are often much slower than LAN links, those WAN links would tend to be deemed to have a high cost, you could end up with all the WAN traffic directed to the WAN link that happened to have the lowest MAC address (or based on one of the other STP resolution criteria.)

It would, however, be quite unusual for multiple WAN links to be joined together remotely in a common tree -- rare enough that

*probably* it would only occur if you were deliberately bridging BPDU from a remote site to implement an extended LAN.

If the WAN links sent you BPDU at all (which is not particularily likely) then they would very likely appear to be distinct leafs, to be detected by STP as not having any topology loops. There might be a layer 3 topology loop involved, but STP is not designed to detect layer 3 topology loops.

If the STP has determined that a particular WAN link is a leaf, then when that WAN connection goes down, if you are using classic STP then the spanning tree will be recalculated -- and will be determined to be exactly the same as it was before. If you are are using RSTP (Rapid Spanning Tree Protocol) then in the same circumstances, the switches would have figured out that that WAN link was not a potential backup link, and so would know that the topology would not change, and would supress notification of the event to the other switches.