Hi Tenno!
We are detecting instances of Matchmaking and general Connectivity issues among Warframe players right now. We are working with our Network partners to diagnose and fix the issue. We will keep you posted!
Thanks for your patience.
EDIT: Our network partner identified a service impact that is causing outages for numerous clients, including us. We will keep you posted!
EDIT 2: Our network partner believes they have resolved the issue and we will monitor to confirm!
EDIT 3: We believe we are now in the clearly completely - relog if you are still having issues.