Some people seem to think that Russia is on Iran's side because they have been working together in Syria to preserve the Assad regime.
This is incorrect because Russia and Iran are historic enemies who have fought many wars over the ages.
Russia is only looking out for its interests, which is partly preserving its ally Assad, but mainly keeping its expanded air and naval bases in Syria. These provide Russia with presence in the Eastern Med, a crucial warm water port and air & anti-air missile coverage over much of the region. Its what the US had in the Cold War from Turkey (and is now losing).
Russia has used Iran to provide cannon fodder to defeat the Syrian rebels.
Now that job is almost finished and Iran is trying to build a permanent military presence in Syria to attack Israel and threaten the Sunni Arab states such as Jordan, Egypt and Saudi Arabia.
Russia has no use for this, but doesn't want to disrupt the final cleanup operation against the Syrian rebels (or look completely traitorous to Iran).
So it is now allowing (using) Israel to kick Iran out of Syria.
End result is that Russia controls the western side of the Euphrates while the US & Sunni allies control the eastern part.
Putin is a brilliant strategist & tactician who plays a relatively weak hand very well.