Micah Halpern reports that there already is a no fly zone in Syria. It was created by the Russians.
…Israel and Russia have gone to great lengths to make certain that, at least when it comes to their air-forces flying over Syria, they are on the same page and there will be no problems. There have been face-to-face meeting between Putin and Netanyahu to iron out any issues and to secure lines of communication. Putin has said that Israel can and should defend herself. Israel has said that they are not taking a side, but they will certainly prevent weapons from being transferred into the hands of Hezbollah. If need be, they will also retaliate when necessary. Russia will be informed by Israel in advance but may not pass a warning on to Israel’s target. These are the terms of Israeli and Russia’s agreement.
That leaves 11 other countries, including the United States. The US and Russia are on opposite sides of almost everything when it comes to Syria. And given the current status of the Russian defense system, the other air forces are, effectively, now grounded.
Read more here.