we configured a pair of remote site routers with : "dlsw transparent redundancy-enable" and they conected with two local LAN swtiches e/g C2950 for end-user connection. However we found the traffic is looped among the routers & switches when some unicast traffic is sent to the end-users workstation from the central site. Kindly advise the possible cause ?

This sounds like a Broadcast Storm. http://support.3com.com/infodeli/to... There is a service that stops this so that you can configure redundant routers called STP but it is not available in all routers. Those that have it usually have it enabled by default. http://www.oreillynet.com/pub/a/net...

I seem to recall STP spanning tree protocol is only for switches or if you are bridging. http://en.wikipedia.org/wiki/Spanni... Question is why did you engage dlsw transparent redundancy? Didn't sound like you have redundant routers between sites. Problem with unicast? Why? I could see if it was broadcast but unicast?