Version per distro

ROS 1

ROS 1 distros use major version 2. The minor is usually bumped for each new distro.

Distro	Versions
Indigo	2.4.x
Jade	2.6.x
Kinetic	2.5.x
Lunar	2.7.x
Melodic	2.8.x

ROS 2

ROS 2 distros use major version 3. The minor is usually bumped for each new distro.

Distro	Versions
Crystal	3.2.x
Dashing	3.3.x
Eloquent	3.4.x