Halo Reach servers are (CURRENTLY) working.

The servers have been down but are temporarily up

While they may be operational, there is going to be maintenance performed on them starting tomorrow

You can keep up to date with that in this thread: https://www.halowaypoint.com/en-us/forums/36cecc379ca14abd918029d359551927/topics/reach-halo-3-odst-maintenance-5-29—5-30/408b60be-3604-4769-bd4e-bccccba64e38/posts