Many years ago in the Lebanon, before 1989 anyway, when Beirut was beset with kidnappings and hostage-taking of foreigners as part of the seemingly interminable civil war, even diplomats were vulnerable. One day a Russian embassy official was kidnapped. By the end of the week he was dead, but so were his kidnappers - their bodies found with their amputated genitals stuffed into their mouths. It was commented at the time that this was the work of the Spetznaz. And that Russia never again suffered a kidnap attempt in the Lebanon.
As it seems increasingly likely that ISIS put a bomb aboard the Russian jet, my advice to Russia is unequivocal; kill ten Islamists for every Russian who died on that flight. Use thermobaric weapons in Syria to bomb the bastards back to pre-Islam without harming the archaeology if you like. But make sure ISIS gives you 2,240 corpses before you bury the last of your people.