Fractional Captain reported experiencing GPS interference while flying over northeastern Egypt. The flight crew preemptively prepared to have backup navigation sources and stayed on course.

Narrative

FL430 Mach 0.85 cruise. Night. Our route during the incident time frame was PASAM N316 HGD V608 NABED ZZZ ZZZZZ. Shortly after PASAM; Red Sea to about 100 NM into Egypt; we encountered GPS interference that lasted until after NABED. The signal of both GPSs disappeared and the FMS reverted to DME/DME for about 30 - 60 seconds. The GPSs came back online for a few minutes and then went out again. This repeated through the affected area. There was no spoofing - false positioning signals. We stayed on course the entire time. In anticipation of encountering interference through this region; we were manually tuning VORs to ensure we had as many backup navigation sources as possible. The FMSs also automatically select additional DMEs as part of its navigation source. As expected; when both GPSs were out; we also got an amber ADS-B OUT FAIL CAS message. Since this did not affect our ability to navigate and it's been a known issue in this region; we did not notify ATC of this issue. This is further validation that there is GPS interference in northeastern Egypt. Crews be prepared to revert to an alternate navigation source if your FMS doesn't do it automatically.