It had to be a big missile at the altitude it was hit.
Pro-Russian separatists announced shortly before news of the 777 downing that they had shot down a Ukrainian transport plane. The separatists deny firing at the 777, but unless Ukraine is short an Antonov, it seems likely that the separatists did it--albeit by mistake.
I have to believe Russian air defense wouldn't make that error.
And it makes no sense for Ukraine to even have their air defense missiles active when Ukraine is using air power. I have to believe their ability to deconflict the air space precludes having aircraft and air defenses active at the same time at the same place.
But with wreckage in Ukrainian territory, there will be answers.
I wonder if NATO AWACS planes have coverage that far east?
UPDATE: Thanks to Stones Cry Out for the link.