may be someone had experience with a following problem:
there are 2 locations which are connected via SDH ring, they are 200-300 km away from each other.
We're trying to connect C3550 on one site with C3560 on the another site. There is no loop, simply a single trunk connection.
The link comes UP but after some seconds the port on one site (always C3550) goes in block mode with the log message "Loop detected on the interface ...."
after disabling Spanning tree on that interface it went UP and satys active without any problem.
What I can see that on the C3550's interface the "keepalive" is active (I suppose it's default), I didn't try to disable it yet but I think it cause the problem but I can't explain why.
The question: is there any distance (in km or time-responce) limitation for STP?