vphen: Proxy can ignore the request, but server can ban the connection if it will flood shares above the requested difficulty. It is not about protocol, but more about server implementation. As a stratum developer I'd like to ask you why you would want to ignore such command from the server?
when several rigs point to one proxy, on server side, will it think that's one high speed rig?so that each rig may get a work that difficulty larger than 1, will it be not so good for each rig?
Yes, the proxy will think it's one high speed rig. That doesn't actually matter though. Whether you're running 50 100 MH/s miners or 1 5 GH/s miner, a higher difficulty will result in the same number of shares returned [minus a very small (< 0.1%) overhead in the mining software].
If you are the only user on your proxy, the only downside to a higher difficulty applied to all your rigs is the speed estimate percentages (individual workers) will have higher variance. Your net speed estimate (all rigs combined) will not have much variance.
