Air carrier Captain reported experiencing GPS spoofing upon entering the Cairo FIR.

Narrative

Safety and security report for Aircraft X ZZZZ - ZZZZ1.On Day 0; Aircraft Y ZZZZ2 - ZZZZ experienced what was initially thought to be an internal navigation failure or perhaps GPS jamming due to previous experience with GPS jamming; it turned out to be GPS spoofing. Reports previously filed. We were the operating crew. This was a high stress event as we had never experienced GPS spoofing. We thought we had an internal navigation failure.On Day 1; we briefed a contingency plan in the event of GPS spoofing entering the Cairo FIR. The contingency plan was to inhibit GPS updating at KITOT and enable GPS updating upon leaving the Cairo FIR at TANSA. At approximately XA:00; several miles prior to KITOT; the GPS spoofing began so we immediately enacted the procedures. iPads immediately positioned themselves over HEAZ; Cairo Airport. An ACARS message was sent to Operations; bringing them into the communication loop as to what was happening with our flight. We were on frequency but due to frequency congestion and inability of the controller understanding English; we did not advise of the GPS spoofing; frequency congestion was in part exasperated by the controller's lack of knowledge of the English language with many aircraft that were on the frequency. At approximately XA:12; the iPad's moved position to OLBA; Beirut Airport. This information was relayed to Operations who relayed back to us that they also showed via Flight Tracker" as being over OLBA. It should be noted that the position on the iPads was stationary and didn't move/track as would be an indication of being in flight. GPS spoofing appeared to have ended approximately at XA:25 and we were handed off to [another frequency]. I continued to monitor position with ground-based navigation updating as well as "pilotage." Once the aircraft was over TANSA at XB:15; we terminated the GPS updating inhibit procedures and continued to CDG (LFPG) without any further non-normals. This was also communicated via ACARS to Operations.It is with my strongest recommendation for security and safety of flight that future crews are briefed from Operations before each flight that transits the Cairo FIR until this security threat to navigation has been corrected. I further recommend that the procedure outlined as we performed for flight be done at least 10 minutes prior to reaching the Cairo FIR and terminate upon exiting the FIR boundary; this should be standard procedure until further notice. Additionally; there is a website that provides GPS interference information. I highly recommend that the pictorial of the area of flight with potential GPS interference be included as we do with weather radar reports in the flight plan package."