Air carrier Captain reported losing GPS functionality for the rest of the flight due to GPS jamming and spoofing.

Narrative

Enroute entering the Cairo FIR the GPS began to drop out due to jamming. We ended up losing both GPS positions during our transit of the Sinai Peninsula and the Gulf of Aden. This area has extreme jamming and spoofing. Our GPS was lost for the rest of the flight and didn't reset after landing. We received multiple unable RNP messages during our flight and split positions during the flight when the right FMC dropped out momentarily. I used a free app I found to plot location from ground aids. This did become hard as multiple VORs in the area were not broadcasting radial information. One of our IRS positions drifted almost 9 NM from the aircraft. This all combines to make it exceptionally challenging to pass through this area.Cause: Poor risk assessment of the flight route by Dispatch routing through this airspace where military grade GPS interference is intentionally being broadcast.Suggestions: Avoid the Sinai Peninsula and the northern part of the Gulf of Aden unless going into Jordan as a destination. Deploy the app to an aid in positional cross-check and GPS spoofing detection. Add warning note to all flights transiting the area. Currently no mention of this area is made regarding GPS interference.