Russia, Armenia, Belarus, Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan agreed to work on a unified Commonwealth of Independent States (CIS) air defense system in 1995. Separate Russian-Belarussian and Russian-Kazakh joint air defense systems are already in place.

https://themoscowtimes.com/news/russia-launches-air-defense-exercises-with-6-cis-allies-over-100-warplanes-63007