NRS is used to exchange presence and session information, which is needed to establish squads. Unlike other server infrastructure, there is currently no self-hostable NRS server due to abuse concerns. However, a partial NRS reimplementation for versions 35.5.0 - 41.0.x is currently hosted publicly. You can configure SpaceNinjaServer to instruct your clients to connect to it like so:
"nrsAddress" to "nrs.source.wf""dtls" to 99