Is the website of the Mongolian railways down? How do I book tickets?

[I35TX]

I didn't personally end up using the train to cross the Mongolian border, but wanted to drop another potential option for buying train tickets in advance. Seems like mongoliatraintickets.com should be a decent way to buy tickets from Mongolia to China/Russia in advance (I believe they only can arrange tickets that originate in Mongolia). They take care of the process and give you the tickets when you arrive. Their instagram, @mongoliatrainticket was also kind and helpful in answering many questions we asked about scheduling, etc.